Talk:Body mass index/Archive 1

Archive 1

Mass, not weight

In SI units, weight is expressed in newton. Mass is expressed in kilogram. I know the general population fails to distinguish between the two, but still BMI should be defined as mass(kg)/height^2 (m^2) --Preceding unsigned comment added by 81.11.170.162 (talk) 18:29, 3 June 2009 (UTC)

agreements with box

I agree with the observation above. The calculator on "The Department of Health and Human Services" website does'nt give any warning or notice to the fact your mentioning, I think it's a responsibility the owner of all the BMI-calcs has to take, likte the guys who run more serious calculators. My favourite is The BMI-Calculator which tells you more about the BMI-value, like fat percentage and so on. 130.243.131.226 (talk) 22:05, 12 February 2008 (UTC)

The language in this entry could be a good deal less arcane. 'ectomorphic and endomorphic, as well as mesomorphic?' These are extremely specialist terms... I myself am unaware of their meaning. If someone who is more conversant in these manners could substitute more pedestrian synonyms, it would be much appreciated. -Toptomcat 14:40, 2 November 2006 (UTC)

I agree completely with this sentiment; I have difficulty understanding this article, and I would try to clean it up, but I don't understand the terms. :) In any case, linking to articles about the lesser-known terms would be very helpful. Benklop (talk) 03:39, 17 November 2007 (UTC)

I think that the BMI system is severly flawed. I am a 6'1" (73") 21 y.o. male with a BMI of 29 which according to the system is borderline obease. I am definately not obese; In fact Im very physically fit. I can run 2 miles in < 15 minutes. I ride my bike everywhere and most importantly I am not fat at all. I would consider my ideal body weight to be around 210. Below that people tell me I look gaunt. Yet even when I was that weight, The BMI still considered me severly over weight. The BMI system does not take into account frame size or muscle mass, yet many statistical studies, I believe, are based on simply hight, weight, age and gender.

-Catskul

You might be interested in Paul Campos' The Obesity Myth, which argues that current obesity guidelines are way out of line. I myself am curious about the history of BMI -- it seems like a very random way to measure people's obesity. --Ryguasu 04:58, 18 Jun 2004 (UTC)

The BMI system seems to be geared toward the average unexercised person, such as myself, who wonders whether they're in shape or out of shape. I do not work out regularly, I eat when I'm hungry, and I have a sedentary job. I'm 5'11", 235 lbs, with a very noticable belly. In short, I am obese. My BMI of 32.6 reflects this well. (Holy ---- am I obese!) It would seem to me to be a useful rule of thumb only before a person starts a regimented exercise and diet routine; after that, more scientific measurements can be used. Either way, and regardless of its flaws, it is a part of established human knowledge, as are the theories of evolution and creationism, and thus deserves to be part of Wikipedia. BlueNight 05:06, 29 Aug 2004 (UTC)

Apparently, my BMI of 19.1 puts me in the "underweight" category, but that may just be a symptom of inaccuracy for children... ugen64 01:50, Sep 22, 2004 (UTC)

There was a not-so-recent article in the New Zealand Herald about the BMI [1], according to the article, the BMI index considers all but one of the All Blacks to be overweight... porge 08:01, Sep 30, 2004 (UTC)

Interesting fact about BMI-skew for athletes: when boxer Danny Williams weighed in for his world championship bout against Klitchko, he was 270lbs. With him being 6'1", that gives him a BMI of 36.9, which is Obese and not far from Morbidly Obese.

If you have lots of muscle, your BMI will be wrong. Simple as. wimbledon andy 13:48, 28 June 2006 (UTC)

Jonah Lomu, a world class rugby player, was 196 cm tall and weighed 120kg - a BMI of 31 (obese). Most top class rugby players have similar BMIs. So the better answer is that the BMI is only useful for someone of average morphology and muscle mass. Lomu would have to lose 25kg, or 60lbs, to get to within the "normal" BMI range, which is clearly nonsense.

Exile 16:54, 11 September 2007 (UTC)

And even better example; Have a look at Markus Rühl and ask yourself if you'd call him "morbidly obese" as the BMI does. wimbledon andy 14:22, 28 June 2006 (UTC)

On the flipside, one wonders if having that much muscle might be unhealty in itself. Personally I always used the BMI index outlined in the Zone. Bedies height and weight it takes into consideration the difference betwixt your waist and your wrist size as well.

Quetelet Index

I believe the Quetelet Index was weight over height, not weight over height squared. I realize many sources don't make this distinction and credit Quetelet with the current formula, but I think this should be confirmed with a primary source, like the text of his book if it's going to be claimed here in the Wikipedia. So although the Quetelet Index may have been an early step along the way, I don't think it necessarily should be equated with what we now call the BMI. --Preceding unsigned comment added by 203.216.99.100 (talk) 03:13, 31 October 2007 (UTC)

Ponderal Index

The article needs a link to the ponderal index. --212.196.144.1 (talk) 10:36, 8 February 2008 (UTC)

BMI controversy

Most of the above criticism is covered in the Obesity article, in the section on defining obesity. In sum, the BMI is not especially well suited for use as a clinical, diagnostic tool. Such diagnosis for each individual is better established using other methods, such as the skinfold test and biolectrical impedance analysis. But that is not the BMI's purpose: Quetelet established the BMI to allow public health statistics to be examined for evidence of weight-related health risks - ie, not for clinical practice. Doctors and health officials can introduce the BMI to individuals as a rough guide to what is - statistically speaking - the optimum weight for their height. But in as much as no individual is an average individual, the statistical picture has to be modified to account for local factors - eg, extreme muscularity. So health 'nannies' shoot themselves in the foot when they make categorical comments about BMI, providing the likes of Paul Campos with an abundance of 'counter examples' proving the absurdity of BMI health pronouncements. Note: the absurdity does not disprove the overwhelming evidence that obesity is a key indicator of health stress, as Campos can be read to argue. It only proves that statistical tools should not be confused for good medical practice. Perhaps the BMI article needs to make this more evident. Adhib 15:02, 3 Jan 2005 (UTC)

It is still relevant to the BMI article that it's been misused. Don't try to whitewash things and restrict their controversy to one single article. Kade 19:33, 24 Mar 2005 (UTC)

Most obesity drugs can only be prescribed when the BMI exceeds a certain threshold. BMI is not too bad as a screening tool. JFW | T@lk 13:22, 27 Mar 2005 (UTC)

Although in the various States of the United States that allow discrimination in medically underwritten health plans based on weight, it is very common for the BMI to used as the sole and only determiner of fitness for medical insurance (and therefore for medical care). Many of the health insurance providers (Blue Cross, etc) attach a sliding scale of massive surcharges to their insurance coverage that goes up based on BMI. Considering their applications take into account a self-reported index (ie, the potential customer simply reports what they believe to be their height and what they believe to be their weight) and all decisions are rendered by computer, this is a woefully inadequate method of determining insurance rates, especially in a country that is so thoroughly geared towards over-consumption. The BMI "may" have some value as a statistical calculator, but it is completely inadequate (and borderline criminal) to use it as a method of denying medical insurance to individuals without them ever being able to be evaluated by a medical professional.

Additionally, the BMI does not take into account gender or age (or fat percentage). For example, women are supposed to have a higher fat percentage than men (20-30% vs. 10-20% for men) - indeed, they need about 15-20% to even menstruate. Further, as individuals age, fat percentage typically increases (consider how estrogen is converted to adipose tissue after menopause). The fact that a diagnostic tool (and a very widely used one at that) doesn't take into consideration gender or age should be included in the problems/criticism section - not just the bits about fat percentage issues.72.196.98.106 07:54, 28 May 2007 (UTC)

Links to BMI calculators

The question was raised whether one link to an online BMI calculator is enough. That would be the case if they had basically the same functionality or comparable ease of use. However, most calculators, like the one by the NHLBI that is currently listed under weblinks only compute and display the BMI value as a number. The disadvantage of this simple approach are:

1. the user does not know immediately how the BMI translates into a weight category (is a BMI of 25.1 kg/m2 "normal weight", "overweight", "obese", "obese II", or "obese III")?
2. the user has to look up the weight category in a separate table
3. the user cannot immediately see how many pounds or kilograms they are into a weight category ("how many pounds am I away from "normal"?). Try this: at a height of 185cm and a weight of 90kg, how many kilograms should you lose to get into the "normal" category? This is the MAIN question users have when they use the BMI calculator. Since the BMI formula is too difficult to do mentally, most people never get an answer to their primary question.
4. people can understand analog displays better when it comes to understanding values that related to other values. In this case the BMI value is compared to both weight (in pounds or kilograms) and the weight categories (normal, overweight, etc.).

I had entered the BMI calculator and scale at http://www.bmi-scale.com into the Wikipedia weblinks section for the BMI article. However it was removed with the comment that there were too mnay links and weblinks should be sufficiently different from each other. The BMI scale at http://www.bmi-scale.com has, in our humble opinion, the following advantages over other BMI calculators we have seen on the Internet:

1. the display shows at one glance, and on one display three values: the users weight, the BMI, and the weight category (normal, overweight, etc)
2. the display is analog and therefor very easy to use
3. without further calculations or table lookups the user can read the answer to their most important question: "how many pounds am I overweight?" No other online calculator provides this, as far as we know.
4. The implementation as an interactive Flash is fun and motivational.

My suggestion therefor is to include the link to http://www.bmi-scale.com in the weblinks section for the Wikipedia BMI article. Unsigned by User:Tom.schulz

Shall we see what the others say before inserting that link? I'm not sure if its merits outweigh the necessity of having Flash installed. JFW | T@lk 22:34, 26 Jun 2005 (UTC)

It does have advantages over the other one, and as long as the other one is available and this identified as needing Flash, it makes sense, as long as other serious defects don't show up. Gene Nygaard 3 July 2005 14:32 (UTC)

There are also BMI graphs around (they are often displayed at gyms). There's one half way down http://www.seekwellness.com/weight/understanding_adult_obesity.htm - but it's too small to be much use. With appropriate values for the bounderies it shouldn't be too hard to create one for here, if a GFDL-compatable one can't be found. CS Miller July 4, 2005 22:34 (UTC)

The graph is just confusing and adds nothing. JFW | T@lk 5 July 2005 08:50 (UTC)

See a list of things above, in the introduction of this discussion thread, about what the interactive display adds to the usability of the BMI scale. TS 22:22, 18 July 2005 (UTC)

The BMI calculator in bmi-scale.com is probably protected by software patents (from the page: It's so unique that our patent lawyers filed a patent on it.). The author of the calculator also requires anyone wanting to use the BMI calculator to get a license (presumably for some fee) from them (from the page: You can license this interactive Flash BMI calculator and scale!). Though it might be OK for Wikipedia to link to that BMI calculator, I think such materials are contradictory to Wikipedia's free principles, and, consequently, many people (me included) probably won't like it. Also, because the page advertises a license for a BMI calculator, the link is probably promotional ones, and consequently, should not be included in Wikipedia. 61.94.148.56 6 July 2005 14:53 (UTC)

As the website states clearly, it is free and encouraged to link to the page. If someone wants to get a customized version for use on their website they need to get a license. It is free to use at the website http://www.bmi-scale.com. TS 22:22, 18 July 2005 (UTC)

Have you read Wikipedia policy on External links, especially the "What should not be linked to" section? 61.94.149.132 05:49, 21 July 2005 (UTC)

Thank you for pointing me to that page. I don't see the relevance though. www.bmi-scale.com is not selling anything. Also, just yesterday I came across a very useful Wikipedia article on low-cost airlines which is full of links to clearly commercial website (the airlines themselves): "http://en.wikipedia.org/wiki/List_of_low-cost_airlines". How is this consistent with the above page? 24.6.153.149 20:59, 21 July 2005 (UTC)

They are allowed because they are official sites — see the exception in the policy page.

Of course, Wikipedia is really inconsistent (there are rules broken here and there — if you search more, you could come up with much longer list). But, just because "there are other inconsistencies", an inconsistency doesn't become a right thing, isn't it? If something is wrong, then it had to be fixed. After all, there are policies that defines which is right and which is wrong (and we shall obey the policies, not other inconsistencies).

No, your site is selling BMI scale licenses (compare with shareware sites: they are providing their programs for free, but if we want to use their programs for commercial or other purposes, we are required to get a license. Are they selling shareware licenses? According to your definition, no).

After all, adding link to one's own [your] site is strongly discouraged (it is your site, isn't it?), especially if your site is selling something (see, you have broken two rules in the "What should not be linked to" section, which I told you to read).

I find those graphs fairly easy to read (but I have a mathematical/science/engineering-type brain). If we ever produce a DVD version of Wikipeida we'd need to license the applet, for a dead-tree version the applet (obviously), wouldn't work. CS Miller 20:38, July 11, 2005 (UTC)

I would like to see http://www.geocities.com/bmind07 link added to the calculator. It is graphic and easy to follow Sheeju 07:57, 8 May 2007 (UTC)

Please chcek http://www.bmicalculatoronline.com. It is easy to use and uses both US and metric calculation Cybosapien 11:02, 14 June 2007 (UTC)

I think The BMI calculator looks better, it's real simple and stylish! --Preceding unsigned comment added by 130.243.131.226 (talk) 19:05, 3 February 2008 (UTC)

Improvement drive

Obesity has been nominated to be improved on Wikipedia:This week's improvement drive. Vote for it there to support the article.--Fenice 20:15, 12 August 2005 (UTC)

Should height be cubed rather than squared?

The standard BMI is a ratio of a person's weight to the square of his/her height.

Does no one but me have the following objection to the standard BMI formula: Since people are three-dimensional objects, it would be logical to relate weight to the cube of the height rather than the square of the height. If the length of a side of one cube is twice that of another cube, the volume (and therefore weight, assuming the same densities) would be eight times as great. This principle applies equally to irregularly shaped objects, such as people.

The person 73" tall feels he is being classified as overweight at too low a BMI, and WHO believes that South East Asians (statistically shorter on average) should be classified as overweight at lower BMIs. These problems both appear to result from the error in the formula--using squares rather than cubes. A person 6' tall weighing 184 lbs. would have a BMI just under 25, as would a person 5' tall weighing 128 lbs. If we compared them by the cubes of their heights rather than the squares, then the 5' tall person would have to weigh 106 lbs. to have the same ratio as the 6' 184 lb. person. The 5' 106 lb. person would be a scale model of the 6' 184 lb. person.

Why wouldn't it correctly be the cubes of the height rather than the squares that should be used?

Olivia 172.152.199.8 03:21, 17 August 2005 (UTC)

I believe this is because human beings do not scale the same in all three dimensions (if an otherwise equivalent person's body is 10% taller than another, that does not mean that he has a 10% larger waistline, for example). In general, height varies much more than width or depth in a human body, so calculating differences in height does not translate the same for the other two dimensions. Cubing the height would not reflect the reality of how the rest of the human body scales with height changes.

The differences for asian bodies (and people of other ethnicities) generally are not due to height, but to genetic differences in the amount of muscle mass present. Asians typically have less muscle mass than caucasians, and thus the same BMI would indicate the presence of more fat. -- Foogod 22:07, 19 December 2005 (UTC)

I find Foogod's comments interesting, but I wonder if he/she can cite evidence. I have my own anecdotal evidence about correlation of width and height. I'm 5'6", and when I weighed 124 lbs., I knew two other young women about the same age as me who weighed the same as me, but both were 3" shorter. So they would have to be fatter than me, yet both wore a clothing size two sizes smaller than me. I have to assume that I was wider but less deep than them, so a cross-section of them would be more round (less oval) to have more area and smaller circumference. -- Olivia

These comments are interesting; but i must present to you the fact that the Body Mass Index is the lowest type of quotient, and is used specifically on sedentary individuals. Myself, for instance; because of my muscle mass (18 stones), i would considered obese, when in fact i am not at all obese in any stretch of the imagination. The body mass index is something used to compare with a chart; it is simply a measurement of body mass not body composition. Regardless of if it is cubed or squared, the values are mostly used for correlation and are a basic calculation used as a basis; i.e. within the obese, it is used to find his body mass index and compare it with a chart; then a dietary or exercise regime can be planned.

Most of your thoughts, are indeed right; but let's remeber that it's used only as a very simple means of calculating mass of those who are sedentary. The article contains this information :-) The magical Spum-dandy 12:36, 30 January 2006 (UTC)

Somebody's added a note to the article to the effect that the measure is wrong because the height is squared rather than cubed. This seems just plain silly. If it were wrong purely on this basis, then somebody would have noticed soon after the BMI was conceived, and it would probably have never become a standard clinical measure, let alone lasted as one for this long. The explanation in Foogood's first paragraph may well be correct. Moreover, even if bodies were supposed to be in the same proportions regardless of height, then weight is not necessarily directly proportional to volume. The typical composition of a human body, and hence the body's overall density, may well vary with both weight and height. -- Smjg 11:57, 20 February 2006 (UTC)

I've reverted your edits partly because they don't seem to be based on any fact, and partly because they made the page look a bit of a mess. Just because a formula is counter-intuitive doesn't automatically mean that it's wrong. Besides, the links appear to be to pages you've created yourself, and they don't convince me any further on the validity of your claim. As such, it looks like original research at best. Moreover, the mere fact that the 'standard' BMI formlua has survived about 170 years already suggests that it was developed on more well-founded research than yours. Please see Talk:Body mass index#Should height be cubed rather than squared? for a more detailed discussion. -- Smjg 12:16, 20 February 2006 (UTC)

Re: the 'standard' BMI formula has survived about 170 years already suggests that it was developed on more well-founded research than yours. Huh? For thousands of years, our ancestors believed that the earth was the center of the Universe. Turns out that was wrong.

Anyway, I'm certainly not guilty of trying to publish original research, because I haven't done much research. All I have done is ask two doctors for their opinion about a 5 ft. 2 in. person weighing 131 lbs. They both said: "Too fat." So I constructed a table using the BMI concept with the height cubed instead of squared and adjusted it so that it would give equal answers at 5 ft. 8 in. What I did was not science. I was just trying to correct an error in the original formula.

All those who genuinely believe that we are two-dimension should not permit any challenges to enter their minds. The only problem is that we are in fact three dimensional. Why resist the truth? Lwiner 21:15, 20 February 2006 (UTC)

And finally, I thought I was making a valid point (that we are three dimensional and a square-based formula cannot be correct) but if there are people here who are so committed to a flat person concept that they remove my comments, I am able to turn my attention to other matters. So, hasta la vista. Lwiner 21:21, 20 February 2006 (UTC)

You miss the point. It doesn't take a rocket scientist to see that the average human being is three-dimensional. When the BMI formula was introduced, there can only have been many people, both laypeople and medical researchers, asking why it's squared rather than cubed. If the answer was that Quetelet made such a simple slip as this, then the work would have been rejected straight away. Therefore, there can only be a more complicated, possibly legitimate reason that Quetelet defined the BMI in this way.

Does anyone have, or know where to find, Quetelet's own literature? This might help put the problem into better perspective.... -- Smjg 19:46, 21 February 2006 (UTC)

Someone alleges in the article, "[T]he majority of the calculation was based on the intuition of its creator, and not through experimental design. ... Quatelet was working strictly from intuition. Unfortunately his intuition was only 2/3 correct." I don't know whether this is so, but we can test the formula against another form of assessing body fat as easily now as then. The mention of skin-fold measurements suggests to me a way of evaluating this formula. I would suggest this experiment: Find about 20 people (maybe fewer) with the same BMI (computed using the square formula we are testing) and different heights, preferably a lot of tall and short people. They would have to be "sedentary," not muscular, and it would be better if they were all the same gender and similar in age. Take a skin-fold measurement of each. Then test the null hypothesis that there is no difference in average skin-fold measurements for tall and short people. -- Olivia, 24 Feb 2006

I guess I should have read this before editing the article - someone will probably revert me. The BMI calculation - as a square - does generate obviously absurd results for people of extreme height. I'm not saying that the exponent should be 3, but it should quite clearly be larger than 2. Otherwise, people who are 7' tall show up as overweight if they weigh 240 lb, and 240 seems like a decent weight for a 7' tall guy. He might even be thin. --Llewdor 22:27, 23 March 2006 (UTC)

The address below provides an abstract of a 1985 paper in the International Journal of Obesity, and indicates a high degree of correlation (0.955 for women, 0.94 for men) between an estimate of body fat derived from the BMI and from some other methods, for the sample population (people attending an obesity clinic). Clearly this is not the last word on the subject (one might ask eg what about other surveys? what about other populations? what about correlation with other methods of assessing body fat? would an exponent other than 2 have offered a better match?). Nevertheless, it does provide an example of evidence that the BMI with a (counterintuitive) exponent of 2 is a useful, simple, approximate measure of obesity, subject to the requirement that the banding criteria (eg the BMI value defining morbid obesity) are chosen to be suitable for the population being assessed.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=4030199&dopt=Abstract

It would seem obvious a priori to cube height rather than square it. I guess the justification comes from empirical studies that find that the squared measure correlates better with other measures of obesity. It would be a pretty basic statistical test to perform these studies and compare the stats for height squared and height cubed. But I can't find reference to any study that has done this - surely it must have been done, given the prominence of this measure. Anyone know of any papers? Until such references are provided, the current text that talks about it correlating "well" is unsatisfactory, as this leaves the question dangling over whether a cubed measure would correlate better.--Nmcmurdo 03:58, 17 September 2006 (UTC)

I think the recent changes are an improvement viz. drawing attention to the raw mathematical property of scalar sensitivity of the BMI. In due course, this could be supplemented by references to empirical work that justify this scalar sensitivity (presuming such work exists). --Nmcmurdo 18:02, 18 September 2006 (UTC)

I guess that you would get something of a flat graph if you plotted weight against height cubed, as they have the same dimensions. I think that there would not be a slope and the the results would be pointless. By plotting the weight against height squared you get a graph with a slope and that is what it is all about. Snowman 18:12, 18 September 2006 (UTC) Crossed out owing to errors. Snowman 09:01, 21 September 2006 (UTC)

For given proportions and density, height cubed would exhibit a well-behaved linear graph in relation to weight, whereas weight will be a concave function (an upward curve that is increasing but by less and less whilst never reaching a plateau) of height squared.--Nmcmurdo 18:22, 28 September 2006 (UTC)

Weight is direction proportion to volume (for material of even density). For bodies of even proportions plotting the weight against height would be like plotting volume against one demension or like plotting x against x cubed. You would get a graph like x = c x y cubed (c is a constant. Snowman 09:01, 21 September 2006 (UTC)

Yep, except the graphs (like the one on the article) tend to have height on the vertical axis, so the curve would be a cube root, i.e. increasing and concave, and more concave the square root.

Regarding, BMI - Should height be cubed rather than squared? Earlier correspondents have asked if there are empirical studies that can determine whether body mass should be assumed proportional to the cube rather than to the square of height. I have searched without success but it's quite easy to DIY using Excel's Charts function. When determining statistically how one value varies with one other it is helpful to confine the study to a population that shows significant variation in the two values of interest but as little variation as possible in other variables. In this case a population with little variation in sex, body type, age and fitness would be desirable. Quetelet studied Scottish soldiers and French conscripts. I now cite analyses of athletes' data. I am not submitting my analysis or conclusions. Instead I will explain my methodology in the form of one example. Those who wish to determine for themselves which power of actual height correlates best with actual mass can follow my method or modify it appropriately: From Si.com, select NBA then Players, download 327 individual weights (Wa) and heights (H) to an Excel spreadsheet. The option of scrolling down to select "PLAYERS BY POSITION" is probably most convenient because each of these seven groups includes 40-50 players. Populations of less than about 100 individuals may be too small to overcome miscellaneous variations, while more than 300 seems to provide a substantial comfort margin. Convert each individual weight to a numeric value in a new column and totalize the actual weight column (SWa). Convert each individual height from feet & inches to a numeric inches value in a new column and calculate the average (Ag). Rearrange the BMI formula from B2=703*W/H^2 with B2 set initially at the "ideal" value of 21.8, to Wp2=C2*21.8*H^2/703 and use it in a new column to calculate Predicted Weights (Wp2) from Height (H) for each individual. C2 is a constant discussed later but initially, set = 1. Similarly, create and use a counterpart formula for the cube option - Wp3=C3*21.8*H^3/Ag/703 Ag is used to ensure that the two formulae give identical answers, i.e. Wp2=Wp3, for individuals of average height. This is just to permit meaningful comparison. Of course, Wp3>Wp2 when H>Ag and vice versa. For each individual calculate Wp2 & Wp3 in appropriate columns and totalize with C2 & C3 initially set at "1". Calculate C2 & C3 by dividing the total of actual weights by the initial totals of Wp2 & Wp3 respectively. (e.g. copy SWp2 & SWp3 and paste special/value into another cell to create a constant value then divide by SWa). When the values for C2 & C3 are returned to each individual Wp2 & Wp3 formula respectively, the two predicted totals become equal to the actual total, i.e. SWp2=SWp3=SWa. Create an Excel Chart, plotting Wp2 & Wp3 on the y axis and Wa on the x axis using easily distinguishable trend lines, e.g. Wp2 heavy dashed, Wp3 medium solid. Also, plot Wa vs Wa to create a "Perfect Prediction" line for reference. The latter can be simplified by having Excel calculate the minimum and maximum for all of Wa, Wp2 & Wp3 and plotting those two values for both x & y axes in the graph, using a light dotted trend line. Scale both axes the same, e.g. just round down the above mentioned minimum, round up the above mentioned maximum and enter those values as the max. & min. for both axes' scales. I have also tested setting both scale minima to zero to see how closely the extrapolations approach 0,0 coordinates. Next look at the two prediction lines to see which one best fits the "Perfect Prediction" reference line. The multiplication products of 21.8 & C2 and 21.8 & C3 respectively do not correspond to the actual B2's & B3's because these athletes average taller than do the entire population of the world. However actual B2's & B3's can be calculated and averaged if desired using the formulae B2=703*Wa/H^2 & B3=703*Wa*A/H^3. Actually I use A=67 inches, which is the average height for Americans. The world wide average would no doubt be smaller and more suitable since BMI's are universal as well as unisex. I have also run similar calculations and graphs of Wp4, dividing by H^4 instead of H^3 and multiplying by Ag^2 instead of Ag to keep the values comparable with Wa, Wp2 & Wp3. For Wp4 I use a heavy solid trend line. Si.com also provides NFL & MLB and other data. Another good source is LeTour.com. Tour de France riders form an excellent population for the present purpose. A group of men, mostly 20-30 years old all verifiably able to bicycle over 2,000 miles keeping within multiple stringent time limits, must be very uniform except for their variations in height. This data is not quite so easily downloadable as the Si.com data. It will no doubt be argued that these groups of athletes are not representative of the sedentary population but that is equally true of Quetelet's studies of Scottish soldiers and French conscripts. I have found that analyses of different groups of athletes (NBA, NFL, MLB, Tour de France and various subgroups) all lead to substantially the same conclusion, i.e. the absolute values and ranges of weights, heights and BMIs vary with the different athletic types but the relationship between weight and height is similar in every case. I.E., in a formula of the type, W=Constant*H^n + Konstant , "n" always has approximately the same value and "Konstant" ~= zero for every group while "Constant" varies from group to group. Try it out!Xperp 22:14, 3 February 2007 (UTC) Sorry. I seem to have entered my cube v square edit twice. I'm new to this. Would someone kindly remove the first entry leaving the second one intact? ThanksXperp 22:23, 3 February 2007 (UTC) Three typos corrected in my submission of 22:14 Feb 3,2007: in approx.9th line "conscripts" to "convicts", in approx.32nd line "retuned" to "returned", in approx.47th line "A/H^2" to "A/H^3". Also I removed my accidental duplicate submission as mentioned in my request for correction of 22:23 Feb 3, 2007. I took care of it myself. Not hard at allXperp 05:50, 4 February 2007 (UTC)Xperp 14:35, 5 February 2007 (UTC)

At the following url is a fit calculation that comes up with an exponent of 2.59 (about half way between square and cube) [2].Rracecarr 19:37, 21 April 2007 (UTC)

I've read it's an exponent of 2.2, but because 2.2 is closer to the 2 they use the square of the height. I don't think it is cubed because people don't necessarily grow equally in all directions. If you've ever compared a picture of a really tall person to a picture of a really short person by scaling them to the same height keeping all proportions the same, the shorter person is usually much bigger in skeletal structure than the taller person. So growing taller in height doesn't necessarily mean you grow equally proportionate in width and depth.

Just because some doctor thinks over 130lb is too fat for 5ft2 doesn't mean they are correct. What people need to bear in mind is that if people do not scale up proportionately with height then short people may look bigger in relation to their height than taller people of the same BMI (squared). However that doesn't make them fatter, being fat has to do with your total percentage of body fat and not how big you look. For the record I'm 5ft2 and not too far off 130lb but my body fat percentage is in the fit/lean category. Unfortunately doctors don't always get it right.

Of course an exponent of 3 is geometrically correct. Just because they have used an exponent of 2 for so long is no justification of its correctness: life insurance companies have been using an exponent of 1 (i.e. linear tables) for even longer! You can still find linear formulae being recommended on the web. Yes, the is good overall for an exponent of 2, but that is because most people are not short or tall - that where the square formula gets increasingly inaccurate (even the linear formula is accurate over a limited range.) I recall some work done years ago where an exponent of 2.7 gave the best fit against actual height/weigh data. But even that is misleading: best fit with actual population data does not equate to least health risk, and the "experts" seem to forget that that is the real aim. --David Broadfoot (talk) 04:31, 26 February 2008 (UTC)

Evidence that slightly overweight is healthier?

The article currently contains the following statement:

Some evidence exists that people with a BMI that would classify them as slightly overweight (25-27 for average Caucasians) actually live longer, healthier lives on average.

Does anyone have any references for this statement? If references are available, they should be provided.. if not it's arguable this statement shouldn't be included if it's unsupportable. (I also ask because I'm curious myself about the evidence mentioned and would like to research this further, but don't know where to start) -- Foogod 21:56, 19 December 2005 (UTC)

Update: After some digging, I did find a reference to this in the Health Policy Institute of Ohio document linked to at the end of the article. There is apparently a finding of reduced mortality rates in overweight people relative to "ideal weight" people in a 2005 NIH/CDC study, however this study does not appear to speak towards "healthier lives". Any other references anybody has to these sort of studies of this would still be welcome. -- Foogod 19:14, 20 December 2005 (UTC)

• The following well-publicized, peer-reviewed JAMA article is probably the best reference for the evidence that those in BMI 25-30 have lower overall mortality than those in BMI 20-25. [3] Peachy1 20:33, 20 January 2006 (UTC)

I read this study and I don't agree with your conclusion. The least "excess deaths" occurred at "normal BMI of 18-25". The number of "excess deaths" definitely increases as BMI goes up. "Excess deaths" actually double with each jump in BMI class, according to the numbers posted in this study. 68Kustom (talk) 00:03, 21 February 2008 (UTC)

Update2: I read an excellent explanation of the seemingly contradictory evidence that the slightly overweight live longer. The life expectancy study is inclusive of everybody, especially smokers. However, smoking can shorten life by up to 10 years. Smokers also generally weigh less. Cessation of smoking, on the other hand, results in weight gain. Therefore, if only lifelong non-smokers are included when comparing longevity, the slightly overweight would not live longer. But when everybody, including habitual smokers and reformed former smokers, are included, the population studied will include the last group, who will live longer than smokers but will gain weight, and smokers, who weigh less but will die at lot sooner. LoopTel (talk) 19:45, 16 June 2008 (UTC)

A very logical explanation. This leads to 2 questions. One, can you find a suitable reference that says that, so that it can go into the article? Two, has a similar study (or a re-analysis from the same data) been done that does not include smokers and former smokers? --AliceJMarkham (talk) 02:25, 17 June 2008 (UTC)

Working on a cleanup and slight de-muddification of facts

Hello,it's Spum here, registered Dietician/Nutritionist and training Physician. I think the article could do with making more condensed and more informative. Definately, the concerns of the above are correct, however, the Quatelet index is not, to all intensive purposes, a way of measuring body composition, but merely a tool used to show the median possibility of injury or illness, but more specifically should be used at the discretion fo the dietician; something which i use only for those who rarely do exercise or are sedentary in their nature. Of course for those of an athletic nature, Computed tomography, Magnetic resonance imaging, or BIA would be more suited.

If nyou have any further questions you wish to ask, please do not hesitate to drop me a message! The magical Spum-dandy (talk)

Mass is not Weight (updated)

Where the article often says the word weight (like in the BMI eqn.), it shold say mass. Mass is the amount of material in an object (SI unit kilograms, imperial unit pounds), while weight is the force of gravity on the object (technically measured in Newtons). If someone where to go to Earths moon or Mars, their weight wold change (gravity is lower), but mass would not and they would still have too much fatty material. However, it is possible that the extra mass would not cause that much damage if gravity was reduced (so the "weight" term in obesity management is really accurate. Did anyone ever investigate this possibility (and find it correct), or should the weight it the equation be replaced by mass? Polonium 20:07, 2 February 2006 (UTC)

You're correct for the most part; however, the calculation is correct in having "weight"; mass is a quotient which takes into consideration more than one dimension; eg the mass of a cube, or soforth. Upon this, the term "BMI = mass / height squared" would actually be a recursive calculation because in this particular instance, the mass is calculated using the body mass index. Nevertheless, the lower portions which i have not cleaned up are quite old and therefore do have some errors. The magical Spum-dandy 20:15, 2 February 2006 (UTC)

No, if someone were to go to the Moon or Mars, their "weight" would not change as that term is quite properly used in medicine and physiology. It can say mass (a synonym in this context), and may keep people like you from becoming confused when it does, but it is not an error to call it weight. Gene Nygaard 15:09, 23 March 2006 (UTC)

Mass is measured in Kg (S.I.) Weight is measured in Newtons, which actually means Mass(kg)* Gravity acceleration(m/s^2) (S.I) If you are measured on earth, gravity acceleration = 10 m/s^2 (S.I.) If you are measured on the moon, then it's different. For example, if your mass is 60 kg (S.I.) then your weight (on earth) is 600 Newtons. so there you go, plain physics, plain english.  :)lila

OK, this is the best place I could find to put this comment: muscle does not weight more than fat, as was stated in the article. A pound of anything, is equal to one pound of anything else. I have changed the line in the article from "muscle weighs a great deal more than fat" to "muscle is denser than fat." --Scottclemens 18:25, 25 April 2006 (UTC)

Scott great point, it reminds me of the old joke, what weighs more a pound of feathers or a pound of nails....? BMI was discussed in-depth by several top bariatric surgeons recently in some recorded interviews. --Preceding unsigned comment added by 68.161.190.158 (talk o contribs)

The updates

• Just adding my two cents (and late in the game too): Sometimes scientific terms should be avoided when writing an article geared to the (very) general public vs. a more scientific audience. The user Polonium is correct scientifically: mass and weight are two different things. But when we're really splitting hairs on this body weight vs. body mass issue in it's broadest context, he's not correct. (I've explained the reason for this below). Contributors to this article must remember the golden rule of technical writing: your work must be as easy as possible for your target audience to understand. A scientific paper on cosmology must necessarily use more advanced terminology than an encyclopedic article on cosmology. Similarly, if your average reader goes to an on-line BMI calculator where they are instructed to "enter your mass," unnecessary confusion would result. In accordance with the basic rule of "avoid unnecessary confusion for your target audience," on-line BMI calculators instruct the user to enter their weight into the field. This Wikipedia article should observe the same practice. Sometimes scientific rigor must be sacrificed for non-scientific audiences -- but that's not necessary in this case. The same issue arises with many other terms, such as "fluid." To "common folk," a cleaning fluid would always be a liquid. Engineering-wise, a fluid can be a gas, liquid, or super-fluid.
  
  As to why Polonium isn't correct (as the larger argument specifically applies to this article), here's why: Mass is constant whether you take the measurement on the Earth or the Moon. If you use a doctor's-style, balance-beam scale (the original, Healthometer-style ones), your obtain the same reading on the Moon as on Earth because they really and truly measure mass. That's because the lighter gravity on the Moon makes both you and the counterweights lighter; you get the same reading. All pure-balance-beam scales (including the Ohaus-style sliding-weights gram scales used by scientists) measure mass. However, most people use spring-based bathroom scales. Spring-based scales measure weight, (a force) not mass. Furthermore, the newer load-cell-based (electronic) scales for weighing people at doctors' offices also measure weight, not mass. So too do the newer digital bathroom scales. Accordingly, instructing someone to "divide your weight by the square of your height" is actually much more technically correct for the largest number of people. By far the largest number of "body weight" measurements are actually and very truly weight measurements. Accordingly, the units of measure to express body weight are "pounds-force" and "kilograms-force" (both of which are legitimate units of force often used in pressure measurements as well as in structural calculations). So in this instance, no scientific rigor whatsoever must be sacrificed when talking about body weight. And we get to use easier-to-understand language too!
  
  Accordingly, I've revised the introductory sentence to the formula as follows:
  

“ BMI is defined as the individual's body weight divided by the square of their height. The formulas universally used in medicine produce a unit of measure that is not dimensionless; its unit is kg/m². Body mass index may be accurately calculated using any of the formulas below. ”

Greg L 22:32, 3 February 2007 (UTC)

• Okay. So you've gone and replaced almost every reference to "mass" with "weight". Except that you forgot the most fundamental of all. The article is about body mass index. If it was about body weight index, I'd agree with your edits. What would have been far more appropriate would have been to add (weight) immediately after the first reference to mass in the article and left every other occurrence as mass. Of course, what you've done is a dialect change from non-US-english to US-english, since the US is the only major country to persist in using the word weight where most other countries have moved to the more scientifically valid term mass, usually with the general usage being that the two are synonyms. The difference between weight and mass as you've described is not sufficient justification to change the dialect of the article contrary to the article title. --AliceJMarkham 22:31, 3 February 2007 (UTC)

• "Okay. So you've gone and replaced almost every reference to `mass' with `weight'." Alice, please be precise and tone down the hyperbole. I replaced three occurrences. And all three were the earliest ones in the article -- in or near the formula -- where language should avoid being overly technical or confusing (as "accessible as possible to a general audience"). There are still twenty other instances of "mass" in the article. What I essentially did was carry "weight" forward one more paragraph (past the very first paragraph where the term "weight of a person" appears).
  
  My basic points are two fold: 1) most weight measurements are truly and scientifically body weight measurements, not body mass measurements (see my two-paragraph entry above for why this is the case); and 2) on-line BMI calculators (such as these first nine Google-search examples here, here, the NIH here, the CDC here, here, here, here, here, and here), all have a field where users enter their "weight."  Even the World Health Organization's data page ("BMI classification," here) on which this article's graph was based says BMI "...is defined as the weight in kilograms divided by..." (my emphasis). This is all for good reason: because "mass" is confusing for too many people. This Wikipedia article should observe the same practice at this early point in the article (and probably even later into it as well); this much is just simple common sense in good journalism.
  
  As regards your "[This article is] about body mass index...[not] body weight index"-argument, I should also point out that all ten Web sites cited above seemed to have survived just fine even though they use the term "weight" on Web pages dealing with "body mass index."
  
  As regards the "American-english vs. other English" issue you cite ("of course, what you've done is a dialect change from non-US-english to US-english"), throughout this article's history -- from its inception in Dec. 2001 until this 7 Dec. 2006 version -- it has used "weight" in the BMI formula and its introductory sentence. The change to "mass" was an ill-advised change made late in the game after the article had been well established. So if what you say were really true (it's an issue of American-style English), then per Wikipedia: Manual of Style: Disputes over style issues, the term originally used in the article by the first major contributor(s) should be retained. I guess that would be my third point.
  
  And not that it matters (because the original usage should be retained for other reasons), but as regards your "other countries have moved to the more scientifically valid term mass"-statement, are you really trying to say that English-speaking peoples outside of America commonly (conversational usage) use the phrase "my body mass" when referring to their weight? That frankly sounds like a big, steaming, metric ton of weapons-grade bullonium; particularily in light of the Geneva-based World Health Organization's Web page, and especially given that User:The magical Spum-dandy -- who is obviously from England -- posted the box statement at the top of this very discussion page in which he wrote "I myself weigh over 18 stones" (my emphasis). Greg L 03:34, 5 February 2007 (UTC)

• "...are you really trying to say that English-speaking peoples outside of America commonly (conversational usage) use the phrase "my body mass" when referring to their weight?"
  I dont, and i live in europe, but i do count my "weight" in kg (mass unit) - as do all europian countries (apart from uk i think)!! So i guess your point doesnt actually stand. And dont be so passionate about it, its just a forum after all, its meant to be for people to discuss and express their views :)

You missed the point. The issue is whether people use the phrase "my weight" or "my mass." Even though the unit of measure is the kilogram (a unit of mass that also happens to have a weight of one kilogram-force), it doesn't change the fact that the term "someone's weight" is so commom a phrase that all institutions such as the World Health Orgainization and every BMI-related site still call body weight "body weight." Greg L (my talk) 16:56, 13 August 2007 (UTC)

• I removed the usage of the phrase "a person's weight rather than their mass". In the context of BMI, the word "weight" means mass, regardless of how it is measured (i.e. it is a measure of kg not Newtons). By saying that BMI uses "weight" and not "mass", the phrase implies that "weight" and "mass" are different (which is incorrect in the context of medical usage). The only correct distinction is when the words appear in the context of physics. A reader who is aware of this difference would interpret the usage of "weight" in that phrase, which must be distinct from "mass" if the phrase is to make any sense at all, to mean gravitational force, and would then wonder why a person's BMI should depend on the gravitational field they are experiencing. A reader who is not aware of the difference would interpret "weight" and "mass" in that phrase to mean the same thing (mass), and would then be confused by the phrase implying that they are different. If anything, the phrase should be "a person's mass rather than their weight", since the only meaningful context in which the words mean different things is physics, and the measurement used in BMI is then mass not weight. However, in light of the previous comments, I believe the distinction between weight and mass should be elided. People are either aware of the difference, in which case they're smart enough to recognise that colloquially they mean the same thing, or they don't know the difference, in which case drawing a distinction is only confusing. --The preceding unsigned comment was added by Hearnden (talk o contribs) 23:06, 5 May 2007 (UTC).

• Weight *is* different from mass and this is about the body mass index. If you were in space you would be weightless but your bmi would not be 0 as it is mass. Mass is the correct term and is taught as such at even basic high school science classes. byo (talk) 15:33, 14 November 2008 (UTC)

Underweight

I'm a student currently researching BMI and I noticed one of your facts are wrong. Underweight starts at 18.5, not 20. You can check the Center for Disease Control and Prevention if you feel like it. --Preceding unsigned comment added by 156.63.190.132 (talk o contribs)

Maybe you can provide a citation for not only this fact, but some place where this particular United States agency was given the authority to determine this interpretation not only for everyone in the United States, but for everyone in the rest of the world as well. Gene Nygaard 15:05, 23 March 2006 (UTC)

Underweight-healthy boundary

Nobody seems sure of the lower bound of the ideal BMI range. I've seen it variously given as 18, 18.5, 19, 19.5 or 20. But this is probably the first source I've seen that gives separate figures for male and female.

And this looks nonsensical: "Human bodies rank along the index from around 15 (near starvation) to over 40 (morbidly obese)". The average for a newborn baby ATMS (20", 7lb) is 12.8. When you get to babies that are born skinnier than usual, it would seem silly to claim that they're still around 15. -- Smjg 14:42, 3 February 2006 (UTC)

Just to point out; The body mass index takes height into consideration as well. Take a look at the chart on the main article. The magical Spum-dandy 13:58, 4 February 2006 (UTC)

As well as what? It would seem obvious from what I just said that I know what a body mass index is. -- Smjg 16:36, 7 February 2006 (UTC)

What is this about?

I have only read the intro and briefly skimmed the article, which should be enough to get an idea of that the article is about. But it isn't. At first I thought this was a statistical thing, a method to record the actual height-to-weight ratios. But then I got the impression it is about determining if one is overweight. The intro should state more clealry what it is about. Also, if it is about the latter then there should be a clear link to any article about the former (and vice versa). DirkvdM 11:04, 6 February 2006 (UTC)

Well; it should be taken into consideration that the lower sections of the article have not been clarified by myself. The idea of the body mass index is that, it is a simple quotient of body mass; from which, it can be calculated if somebody is overweight. Similarly, it can used to check for ideal body mass or the body mass of the underweight; but that is not the direct nature of the body mass index.

Just as you can use a speedometer to see if you are speeding, it is not made solely for that purpose; The idea of the body mass index is that it is used as a simple means of calculating the body mass of sedentary individuals. From this data, it can then be compared with a chart to determine obese or underweight individuals, but it is not specifically used for that. The basic gist of what i am saying is that the Body Mass Index, itself, ONLY calculates the general mass of an individual. Although this can then be correlated with charts, this is just using BMI for another purpose.

The magical Spum-dandy 11:45, 9 February 2006 (UTC)

However all that may be, I somehow ended up here (trying to answer a ref desk question) and hadn't a clue what the article was about. That should be stated way at the top, not somewhere in the middle, so people will instantly know if this is the page for them. More specifically, I was looking for statistics of the general population concerning body weight. And the title suggests this article is about that. So I wasted time reading something that was totally irrellevant to my quest. I gather that in certain circles 'BMI' is a well known thing, but one cannot assume such knowledge and jump right into the deep. There has to be an intro for people who haven't a clue what it is about. It is about checking if one's length/weight ratio is healthy, right? However this may secifically be the case, clear it up in the intro. DirkvdM 12:41, 9 February 2006 (UTC)

Obscure introduction

What does this mean in the introduction?

Despite the fact it only takes into consideration 2 dimensions of the human body, it is only used as a quotient of an individual's body mass, which in clinical practice would be used in correlation with a body mass index chart.

• Does "2 dimensions" mean height squared (rather than cubed) or two variates (height and weight)?
• What is the meaning of "quotient" in this context?
• What sort of "body mass index chart" is implied? I thought the charts simply graphed BMI (often by colour) as a function of height and weight. Or do some charts "correct" BMI categories for height?

Thincat 12:27, 8 March 2006 (UTC)

I have now tried to sort this out myself. Thincat 14:21, 17 March 2006 (UTC)

Means of estimating body mass

The article says

"the BMI is a relatively simple and quick process for calculating overall body mass"

and

"BMI is typically used as a means of estimating body mass".

These statements both seem wrong (and so, presumably, non-verifiable) and yet have been there quite some time. I wonder what is meant? Weighing scales are a means of estimating body weight and, hence, body mass (see weight). BMI is a means of estimating body type or body fat (or words to that effect). This sort of confusion seems to occur elsewhere in the article and I find many parts written in a rather obscure style.

In the human weight article it says:

"Another way of looking at human weight is finding the lean body weight. Lean body weight is essentially your total body weight minus weight comprised of fat."

which I also find rather obscure. However, even there, I do not think it is suggesting "body weight" and "lean body weight" are to be equated. Does anyone have comments before I make some changes? Thincat 14:18, 20 March 2006 (UTC)

Just throw that one-sentence paragraph out, rather than trying to salvage anything. Maybe it was intended to do with something like calculating "ideal" or "acceptable" body mass for someone of a given height, but do we really need to speculate about what was intended? It doesn't make sense; just toss it. Whatever it was intended to say is likely redundant with what is already said; if it make you think of some point not covered, just start from scratch. Gene Nygaard 16:14, 24 March 2006 (UTC)

Imperial units of measurement and image concern

I added a BMI formula that works directly with United States Imperial units, and is in fairly widespread use. It avoids one having to convert to metric first. The conversion factor 703 is sometimes (incorrectly) stated as 704 or even some other value, but using Google calculator comes up with 703.06958, which rounds to 703 with negligible error. I also added a link to the CDC BMI faq which has a similar formula, but moved the 703 to the front, which is mathematically equivalent and much neater.

As for the BMI chart, an outdated "fair use" chart could be better replaced with an up-to-date free image, it is likely that some government site has a suitable one, but I do not have time at the moment to go find one. --Frank Lofaro Jr. 07:33, 26 March 2006 (UTC)

The UK mixed units calculation seems rather contrived. As a UK resident in my 40s I'm comfortable with SI units and if I really felt the need to use the old Imperial units I could use the US calculator. I've never seen this UK formula anywhere except here.

The UK example also seems contrived in that it uses stone for weight and metres for height, I suspect that there maybe a generational thing happening here, but I suspect that if you think of your weight in stone you probably think of your height in feet and inches. Various NHS websites offer both sets of units, for example, NHS Direct BMI calculator pcr^talk 19:01, 28 February 2007 (UTC)

I think of my weight in stone, and height in meters (and im british) but then i think of diatance in terms of cm, meters and then miles, so what do i know... Georgeryall 20:33, 9 April 2007 (UTC)

Showing stones with a decimal point is artificial and not in common use. In the UK, the popular imperial units to use are stones and pounds - fractions of a stone are expressed in pounds. 92.22.79.50 (talk) 09:32, 21 June 2009 (UTC)

Changes to BMI article

I have made a series of quite major changes to the article, mainly to reorganise the existing material into what seems to me to be a more logical order.

However, I have added a new section on how BMI is calculated (partly drawing in material from elsewhere in the article). It seems to me that BMI itself is easily and pretty accurately measured. It is the categorisation based on BMI measurements that causes confusion and dispute. Hence, I have tried to emphasise BMI categories as being a rather separate issue (and one prone to error). I have tried to make a start in clarifying this.

Apart from deleting a sentence and a phrase which I commented on above previously and which I'm sure were incorrect, I have not attempted a detailed critique of the physiological aspects: I am not qualified to do this. I might have a shot at this later, but giving other editors time to examine each point separately. Thincat 12:21, 29 March 2006 (UTC)

Suggestion for BMI FAQ, ideal weight and body fat

Here is a suggestion for ideal weight and BMI calculator at BMI and ideal weight along with a BMI FAQ and 2 different body fat calculators from bmi (with references). I think the BMI FAQ is more extensive than the current BMI FAQ. Thanks Antonia

Underwater weighing vs bio-electric impedence

Underwater weighing is the gold standard, bio-electric impedence is of low accuracy and low reproducibility, being influenced greatly by hydration and skin resistance. --Frank Lofaro Jr. 03:59, 6 April 2006 (UTC)

Correct, but bio-electrical impedence is much more accurate than using the body mass index because it's an attempt to measure body composition directly. The magical Spum-dandy 07:49, 6 April 2006 (UTC)

I personally found the Bio-electrial impedence to be way off for me. Of the three of us that used it, I'm the only one that obviously has extra weight (all of it in the tummy) and yet by that measurement, I had the least. As a singer, I drink lots & lots of water daily. Currently my primary forms of exercise are the weekly chorus rehersals (mostly lungs, but there's some stage movements), and a 1/4 mile walk each way from our parking garage to the office, and when the weather is nice on a work day, up to a 1/2 mile walk during lunch. Joncnunn 18:35, 11 April 2006 (UTC)

Again, they are not meant to be 100% unfallable, and again; biolectical impedence is more accurate. The magical Spum-dandy 21:03, 11 April 2006 (UTC)

Recent news

Authors of this article may be interested in the - sort of related - new childrens growth standards released by the WHO, see this.--nixie 04:08, 1 May 2006 (UTC)

Units

Can someone PLEASE post a chart here in U.S. units? Most of this site's readers are Americans, and we have no idea what you are talking about. A chart with kilos on it signifies absolutely nothing to me. I understand having a metric chart in the spirit of multiculturalism, but please put a U.S. one as well so that we can understand it when we read it.

History21 01:11, 26 May 2006 (UTC)History21

Kilos makes sense, but the charts other option is "stones." Does anyone measure their weight in stones these days?--T. Anthony 21:23, 31 May 2006 (UTC)

Only the WHOLE of the British Isles. And most of Europe uses Kilos. Not everyone uses the same units of measurement as the Americans, though I suspect they would like us to. [G Pearce 15:34, 05 June 2006]

This is an interactive BMI calculator in metric, US, and UK units: BMI Calculator and Scale

I have to say, I use stone. Also there imperial units, not US Units, but thats not important.

Starvation BMI?

One part of this article says that a BMI under 15 is considered starvation, but the scale says that under 17 is starvation... which is it? Melange fiesta 01:10, 20 June 2006 (UTC)

Removed POV paragraph

I removed this paragraph from the problems section, as it is POV, (possible original research) male-bashing feminist propaganda:

"One more problem is that men, in general, tend to over-estimate the amount of muscle mass that they have. Conversely, they tend to under-estimate their body-fat percentage. That causes them to believe that their high BMI is not indicative of large fat stores, and to discount the usefulness of the BMI as a screening tool. Studies indicate that the higher the BMI, the less likely it is to be a result of abundant muscle mass."

I feel text such as this does not belong anywhere but in a leaflet for recrutment, furthering the masses of feminism. Bad ju-ju - Jak (talk) 02:14, 5 July 2006 (UTC)

Questionable validity for tall folk

At 198cm here, I can safely say that the BMI completely breaks down for me as an average build, sedentry man. The only time in my adult life I've been within the 'normal' range is after a 6 week nervouse breakdown where I couldn't eat - I had a concave belly and countable ribs, and still scored high normal in the BMI (see the graph 92kg is high normal).

How the BMI addresses height is important, considering that the population is getting taller on average. If the goalposts aren't moved with the move in average height, more people will be classed obese just simply because they're taller and the BMI isn't classing them properly.

Yes, the BMI may be okay for people of average height, but the taller you are, the worse it gets. According to BMI, someone who is 198 cm (6'5) and weighs 73 kg (161 lb or 11.5 stones) has a BMI of 18.6 and is thus considered "normal", but if you would meet such a person you would think that he/she had recently been released from a concentration camp; while someone of the same height weighing 98 kg (216 lb or 15.4 stones) has a BMI of 25.0 and is thus considered "overweight", although that person would look very well proportioned and healthy. The problem with BMI is of course that it doesn't allow for the fact that people, in order to be proportional, also need to grow sideways as they grow upwards. Many sites covering BMI compound this problem by also mentioning waist circumference, stating that a man with a waist of 100 cm (40 inches) have a "high risk of morbidity" [4]. I would definitely agree if the person's length is only 150 cm, as that means he has a waist measurement which is 75% of his height and consequently looks like an American football, but at 200 cm that measurement is only 50% of the height. A 50% height/waist ratio would give the 150 cm person a waist of 75 cm (30 inches). He would probably still look a bit stocky with such a waist, but wouldn't be regarded a football. Thomas Blomberg 13:12, 30 August 2006 (UTC)

Exactly right. The BMI, calculated on the square formula shows higher weights for short people and lower weights for tall people. The formula is incorrect. A proper BMI would be based on a cube formula. User:Lwiner 00:57 4Dec., 2006 UTC

I honestly believe it's not height that's the issue, it's the fact that you are male. It's often been stated that the BMI range is too low for males. You rarely see a woman your height, but if you did she probably wouldn't have this issue and a much shorter male may still find the BMI ranges unrealistically low. I do not believe people scale up with the cube of the height. Just find a picture of a very short person and a picture of a very tall person and then scale the pictures to the same size keeping all proportions the same. Usually the shorter person has a bigger skeletal frame in relation to their height than the taller person, suggesting people do not scale up proportionately to height. --Preceding unsigned comment added by Dee26 (talk o contribs) 00:56, 21 February 2008 (UTC)

Thresholds

I removed "anorexia" as a threshold. Add it back in if you have a good reference for it, but otherwise I think it is misleading given that anorexia is not diagnosed based on simply a BMI of less than that value. I also removed the reference to "BMI is valid for adults over age 20" because I couldn't find a supporting reference for the age of 20 in particular. Better to say "for adults only" unless there is a reason to be specific about the age of 20. Chartreuse green 21:46, 15 August 2006 (UTC)

Unverified Statements

There are a significant number of unverified statements in this article. I do not believe many of them are accurate. For example:

• The BMI has become controversial because many people, including physicians, have come to rely on it for medical diagnosis - but that has never been the BMI's purpose. It is meant to be used as a simple means of classifying sedentary (physically inactive) individuals with an average (mesomorphic) body composition. That is exactly what it is used for: the medical diagnosis of underweight, overweight, and obesity. When you read medical research papers, they base treatment groups on BMI. They use reduced BMI as a target endpoint.
• The issue with "very athletic people tend to have high BMI's and this is okay" is repeated four times in the article. In fact, the entire article reads as an argument that BMI should only be applied to sedentary people. While this may be a good argument, it is not encyclopedic and should be mentioned a single time only.
• The reason height is squared rather than cubed or raised to some other power is simply that, taken over people of different height, the resulting index correlates reasonably well with degree of underweight or overweight. No law of physics or physiological growth is implied. Is there a reference for this? I had thought that the real reason was historical: Quetelet found that BMI matched his insurance tables well, and then nobody ever changed it later on. BMI is not the "best" way of defining who is overweight and who is not, it's just the one that we happen to use.

Anyways, I'll wait to hear if anybody feels strongly about these before I remove them. Chartreuse green 22:02, 15 August 2006 (UTC)

I agree with the need to question the unverified statement concerning the statistical properties of dividing by height squared. Further, even if a study were to find high correlation coefficients for the BMI and other obesity measures, we still need to have references to studies that find that dividing by height squared performs statistically better than height cubed, given the obvious geometric reasons to think that height cubed would be the better measure. If such studies were not to find this, then I think the text should refer to such a deficiency of the measure. --Nmcmurdo 04:09, 17 September 2006 (UTC)

Thresholds

In the thresholds, the difference between strict inequality and "greater/less than or equal to" is largely irrelevant for a continuous variable where there is little chance of exact equality, so I have made the section simpler and more readable by just giving the ranges without worrying about the form of inequality used at the ends of the ranges -- unless someone can find a source which makes an issue of them. Arbitrary username 13:16, 23 August 2006 (UTC)

Table/diagram of BMI categories

I checked my bmi by estimating using the diagram at the top and using the calculations and got drastically different answers... (ie normal using the calculation and obese using the diagram.) Has the data been checked? 17:47, September 3, 2009 —Preceding unsigned comment added by 69.70.157.158 (talk) 21:50, 3 September 2009 (UTC)

After User:Snowmanradio created BMI Chart (height 150 - 174cm), speedy deletion was rejected and the article (i.e. the table) is now being considered for deletion with an interesting discussion: Wikipedia:Articles for deletion/BMI Chart (height 150 - 174cm). Whatever the upshot, some sort of table and/or diagram of BMI categories would be useful to the BMI article, particularly because the present diagram has doubtful copyright. If it cannot survive as a WP article, the "chart" could be be tidied up and extended to greater heights and included in the BMI article. Probably two versions would be appropriate: metric and "English units". I might be able to help with the table but a diagram is beyond my graphics package capabilities. Any suggestions? Thincat 14:13, 18 September 2006 (UTC)

I can easily make metric and imperial versions of a BMI table with a perl script. I used a limited height range to fit on one page. I was planning several BMI charts with different height ranges. I am anticipating that my BMI chart will not be deleted, but I am waiting for the final decision before extending the height range or elaborating the graphics (I may need help with graphics to convert the table to an image). Snowman 17:05, 18 September 2006 (UTC)

I have uploaded a "free" BMI chart to Image:BMIchart.png which uses WHO's cut-off values. It needs some colors and labels, but it's a start. Contact me if you need it in EPS format (a conversion to SVG would be nice). Woseph 10:18, 19 September 2006 (UTC)

I've now added some color. Any objections to changing from Image:Body_mass_index-weightheight.jpg to Image:BMIchart.png? -- Woseph 11:35, 23 September 2006 (UTC)

Without seeing your comment, I went ahead and uploaded an SVG version that I made. It's kinda awkward since I didn't know that someone else was working on it (Snowman left a note on my talk page and I just went to it). Obviously SVG is a nicer format, but I won't be hurt if it needs to be changed (ie updated with the extra WHO measurements which, to me, are kinda useless) or replaced. Sorry about the duplication of efforts, last time I checked this page I just saw the black and white copy! InvictaHOG 04:05, 24 September 2006 (UTC)

I don't care, as long as we get a good chart for the article. However, I do vote for WHO classifications (WHO being international and so on). By the way, why didn't you include imperial weight measures? (Regarding SVG, I agree and I'll try to get around to converting the EPS used to make Image:BMIchart.png. It's just that I currently don't have Illustrator available.) -- Woseph 11:33, 24 September 2006 (UTC)

I had wanted the title in the picture and didn't think it looked nice with the pounds along the top as well. It's easy to swap out. It won't take any time at all to update the image, so I'll go ahead and add the WHO curves and regenerate it. InvictaHOG 21:38, 24 September 2006 (UTC)

I just uploaded a new version, let me know what you think. InvictaHOG 23:24, 24 September 2006 (UTC)

Were my numbers any use for the new chart? Suggestios: Larger numbers along the four sides, perhaps they could be seen with the low resolution picture (perhaps resized as well) on the article page (useful for WPCD, which does not have high resolution pictures). Put the BMI range for each zone on the chart, perhaps in each coloured zone, so that it is clear if the image is downloaded as a separate item. Stones & pounds in addition to pounds on the horizontal top axis (perhaps written vertically or at 90 degrees), in UK we use stones & pounds (14 pounds to one stone) and every here one will want it converted into stones and pounds, (in USA they use pounds only, I think). Meters and Kg, ok for Europe. Snowman 08:47, 25 September 2006 (UTC)

Honestly, I just learned a new program (gnuplot - it's awesome!) so that I could graph it out and make it more accurate. I didn't have a graphing program and thought I was going to have to manually enter the intersections. I'm not familiar with the WPCD, but will try to read more later. I take it that WYSIWYG as far as the graphics on the page are concerned? Increasing the size is easy - I just need to know how much! It's readable by clicking, but I assume it needs to be legible on the page as is. I can add the ranges to the graph, no problem. As to the stones and pounds...can't we just let people convert? InvictaHOG 11:46, 25 September 2006 (UTC)

• I think four scales is enough, and using both "pounds" and "stones and pounds" would be like using both "metre" and "centimetre" in my opinion. (The latter conversion is easier in base 10, the former in base 14.) Other than that, I just think we could use some more tick marks: I don't think we can expect people to do better than bisect given marks, and ±10 kg is pretty much when it comes to human weight. Perhaps some more grid lines, or minor grid lines as well. -- Woseph 15:31, 25 September 2006 (UTC)

I've made several of the changes suggested here. It looks a little more cluttered than I'd like, so hopefully there won't be any more additions needed! InvictaHOG 01:31, 26 September 2006 (UTC)

It is fine, but I am not sure what the dotted lines indicate exactly. Perhaps these should be labelled too. Snowman 14:31, 27 September 2006 (UTC)

They are an unfortunate side effect of the choice to use the WHO classification, which for some reason decides to randomly divide everything into subcategories which, to my knowledge, have little to no clinical significance. They can easily be removed, but they were put in there because that seemed to be the preference. They are explained in the upload text and can be explained in the caption but I would prefer that the graph not be cluttered any more with labels for seemingly meaningless divisions. InvictaHOG 16:28, 27 September 2006 (UTC)

I strongly disagree that the subdivisons are an "unfortunate side effect". WHO didn't come up with the graded classification of overweight and obese for fun, the did it partly to make BMI more useful in medical studies! For example, say you're trying to study if obesity increases the risk of an heartattack. If you yourself choose the cut-off points you'll get results like "30-32.9: no significant change; 33.0-35.0: 20% higher, significant; 35.1-40.0: no significant change". That makes your results pretty much useless because they cannot easily be compared to other studies without having access to your raw data. However, if you use WHO's cut-off points, your results might look like "Obese class I (a): no significant change; Obese class I (b): 18% higher, significant; Obese class II and III: no significant change." If all studies use the same cut-off points (that is, WHO's classification), it's easy to compare different studies: study 1 might find a 10% increase for obese class I, study 2 a 5% increase for obese class I, and so on. This can not be done if you yourself just randomly selected the cut-off points. WHO has lots of more information available, start with [5]. I believe what it boils down to is the fact that BMI is designed to be used as a statistical measure on a population-level: as an individual, you can't determine if you're fat or not by calculating your BMI.

Having said that, I agree that including labels for the subdivisions would clutter the diagram too much. Removing the extra lines isn't a good idea either in my opinion, we do want some kind of divider between BMI 30 kg/m² and BMI 70 kg/m², right? -- Woseph 11:30, 28 September 2006 (UTC)

Body Typing

I'm thinking of canning the bits about somatotyping. The concepts of ectomorph, endomorph, and mesomorph were developed be a Psychologist for personality testing! They only loosely correspond to real metabolic differences between individuals, and then, mostly by accident. The idea was that your body type was based on what type of embryonic tissue layer you had the most of, and this determined your personality. Endomorphs, for example, had mostly endoderm, which goes on to form the digestive tract. As a result they were prone to gain fat. There were also large, jolly, and lazy.

You can see where this is less than scientific. Bodybuilders like to throw the terms around a lot ("Dude, I can't help it if my gains are lousy-- I'm an ectomorph!"), as do any number of personal trainers and popular fitness writers. I think Wikipedia should probably adhere to a higher standard.

My proposed edit would basically expunge all the Somatotype-related terms and replace them with things like "individuals prone to gaining muscle" for "mesomorphs" and "predisposed to low levels of body fat and muscle" for "ectomorphs." I don't want to make an edit this big without some input, though. Opinions? Kajerm 23:49, 2 October 2006 (UTC)

Whatever we do, it should be backed by references. If there are peer-reviewed references that we could pull together, it might be nice to just mention the ecto/meso/endomorph concepts as products of a failed theory and then present the current way of thinking within the scientific/medical community. InvictaHOG 01:51, 3 October 2006 (UTC)

These words get thrown around all the time - including in science textbooks and the like - so it's certainly interesting to find out that they aren't actually factually based! It would be good to have your comments includd in the article with references. Chartreuse green 06:10, 3 October 2006 (UTC)

Hmmm... I'm all for sourcing and explaining, but somatotypes already have their own article. Not without its problems, of course, but that might be a better place. Perhaps a brief mention (something like "...blah blah blah (with some parallels to the traditional somatotypes of ectomorph, endomorph, and mesomorph)..."))? Kajerm 23:40, 10 October 2006 (UTC)

I think that BMI was intended to be a convenient measurement for people with less medical accessibility to better scales. Something they can do at home on their calculator. Beginning with somatotypes seems completely inappropriate to me. The article should start out simple and then have detailed theories following. Beginning with complex statements about somatotypes seems wholly inappropriate, even before its July '06 update documenting a study contradicting the somatotypes theory. Neilbaby1 12:46, 22 October 2006 (UTC)

Asians?

I assume that references to 'Asian' here refers the common American usage of Asian - i.e. east & southeast Asian; perhaps someone could say if this is so. 62.49.4.39 20:53, 12 October 2006 (UTC)

shouldent you put some averages

i want to suggest that you should put some averages to body mass index weight height and age.. please can you do this from kracrook! please talk to krakcrook if you want to reply! p.s im doing some reasearch in my science class please reply to help me finsih it! http://en.wikipedia.org/wiki/User_talk:Krakcrook

BMI as a measure of healthy mass for skeleton

I note that a lot of people here seem to be rather actively claiming that BMI is meaningless for muscular people.

I have previously come across suggestions that the BMI is in fact a very good measure for if you're overloading your skeleton. I'll have to spend some time finding references to this, but my unserstanding is that the point was that BMI over 25 is overloading the skeleton regardless of whether it is fat or muscle. --AliceJMarkham 07:58, 3 November 2006 (UTC)

BMI will be proportional to height?

The statement "For a given body shape and given density, the BMI will be proportional to height e.g. if all body dimensions increase by 50%, the BMI increases by 50%" has been added quite recently. While this is mathematically correct I think the remark is not too helpful. People's body shape does depend on height. I suspect, for a 50% height increase one might normally expect a weight increase nearer to height squared (keeping BMI constant) rather than cubed (for fixed body shape and increasing BMI by 50%). I am not an expert on body shape and am not familiar with the literature so I am wary of adding any "original research". Suggestions? Thincat 12:56, 10 November 2006 (UTC)

I think it's an important mathematical property of the measure that should be stated. Ideally, it should then be followed by the type of statistical evidence you mention viz. the empirical relationship between height and weight in samples controlled for proxy indicators of 'obesity'. This would help answer the concerns mentioned above over whether the measure 'should' have a cubed rather than squared term (or any other different formulation). I should state I'm not a physiologist, but strangely I have been unable to find any decent peer-reviewed empirical research on this issue - grateful if any physiologists could provide this.

I think a worse option would be to remove the material on the mathematical property and not have any empirical results. This just leaves a dangling question in the minds of any reader with a basic understanding of geometry. --Nmcmurdo 18:20, 10 November 2006 (UTC)

A basic understanding of solid geometry would reveal that BMI formula is incorrect. Using a square function to calculate BMI would be correct if we were two-dimensional. In fact we are three dimensional. Therefore what is needed is a cube function. If this is not obviously clear, consider this analogous problem: if I tell you that the height of cube is 2 meters and the specific gravity of the cube is 1, how would you calculate the weight of the cube? Would it be 2 squared or 2 cubed? Applying this concept to human beings and assuming that taller people are both wider and deeper and that the width and depth are proportional to the height, you would have use a cube function to have a valid BMI. I have tried to introduce this reasoning into the main page and invariably, it is removed by people who apparently have some investment in the old and incorrect formula. User:Lwiner 00:54, 4 December 2006 UTC.

You are wrong to suppose that people who think that BMI is an appropriate measure are ignorant of solid geometry. The issue of what is a healthy weight for people of a particular height is a matter of physiology and epidemiology and not of geometry. A person who is 50% higher than someone else is not typically 50% wider and 50% deeper. People are not like cubes. Anyway, the matter is not even one of typical body shape. Since the BMI is used as an indicator of health it is the correlation between BMI and health status (life expectancy, I believe) that matters. Thincat 14:10, 8 December 2006 (UTC)

It's surely goes too far to assert that the "BMI formula is incorrect" simply on the basis of recongising that humans are three-dimensional. But Thincat's response leaves a number of dangling questions that I think could useful be answered in the article text if decent research on these subjects exist e.g.

• To what extent does non-proportional dimensionality in humans (presumably 'equi-obese' humans) justify dividing through by a square rather than a cube?

• Is the "correlation between BMI and health status" statistically efficient? --Nmcmurdo 18:59, 5 January 2007 (UTC)

• A lot of this debate about squared versus cubed in the formula is kind of missing the key point. Humans do not vary there size in proportion. I am over 20 years old. If I over-eat for a few years and add 20% to my "weight", my height will increase by precisely ZERO. My width ( and depth ) would probably increase significantly. Eregli bob 22:21, 26 January 2007 (UTC)

This text was removed with the reason given: "Removed incorrect assertion - weight scales cubicly with linear dimensions, not to the square. This is basic allometrics". This statement on how weight scales is correct, but it is precisely the reason why the BMI scales with height (for a given shape and density)! I suggest the editor works this through with a pen and paper and a few geometric examples! --Nmcmurdo 18:08, 13 April 2007 (UTC)

BMI to Body Fat Estimator

Added this link to the external sources. Its quite useful, because of its uniqueness, I think. Cheers! --Romansemko 14:05, 4 December 2006 (UTC)

As the discussion on the site shows (as does common sense) it is just not an accurate method. I have removed it. -- Mwanner | Talk 14:52, 4 December 2006 (UTC)

Remove BMI chart?

I've been bothered for some time by the BMI table (referred to as a chart) being in this article. I don't think that it is really useful. It duplicates the info in the image at the top right of the article, but over a more limited height range. Many adults, particularly (but not exclusively) males, would be over 174cm tall. Clicking on the graphic at the top right to get a larger version is far more productive, although I must admit that a larger scale version of that would be even better. The list of ranges at the start of that table is also an unnecessary duplication of the thresholds list earlier in the article. For these reasons, I propose that the entire BMI Chart section be removed. --AliceJMarkham 01:10, 5 January 2007 (UTC)

I made new pages to include taller height ranges and linked them to this page. Snowman 14:41, 26 June 2007 (UTC)

The first linked table passed the "article for deletion" process. Snowman 14:44, 26 June 2007 (UTC)

disambig page

Searching 'bmi' leads you to a page about an airline. Shouldn't it there be a disambiguation page for BMI? BMI is much more well known then BWI and many people would not even know what it stands for and therefore be able to search for Body Mass Index. --The preceding unsigned comment was added by 216.162.240.250 (talk) 20:28, 1 May 2007 (UTC).

BMI Formula: Pound Force?

The word "weight" also means "mass" (see 6a in the Merriam-Webster Collegiate Dictionary). Regardless of the word used (weight or mass), if you want to calculate the Body MASS Index, you have to use a unit of mass (kilogram, pound avoirdupois, stone), not a unit of weight (Newton, pound force). Hence, the word "force" should be removed from the formula. (Note: The pound avoirdupois is officially a unit of mass since it is equal to exactly 0.45359237 kilogram [National Institute of Standards and Technology, 1959]. A bathroom scale actually measures a force but the result is displayed in kilograms [mass] or pounds avoirdupois [mass].) --The preceding unsigned comment was added by 72.196.98.106 (talk o contribs) 2007-05-28T07:54:59 UTC.

I agree. Using "force" in the formulas just makes them more confusing. I'll change it now. -- kenb215 talk 00:52, 29 May 2007 (UTC)

Clothing?Shoes?

Any measurement which purports to be a scientific index should have the inputs operationally defined. If the weight/mass assumed to be nude, and the height without shoes? Shoes might add an inch and a pound or so. Clothing might add pounds more. Nothing in the article appears to address how the height and weight are to be determined. Edison (talk) 18:27, 29 February 2008 (UTC)

Stilts? Backpacks? --David Broadfoot (talk) 02:14, 1 March 2008 (UTC)

When you are on the moon, your BMI has to include the spacesuit. pcr^talk 22:17, 1 March 2008 (UTC)

Nahh... they can just strip off inside the moon lander. (P.S. Do you know how much it costs in fuel to send a set of scales to the moon?!) --David Broadfoot (talk) 03:57, 2 March 2008 (UTC)

Edison, I find your comment strange. The inputs are defined. Height and weight. Of course clothing should not be included and to state as much would be silly. Or maybe you are on to something. Could it be that we don't really have a problem with obesiety, its just everyone is walking around in heavy clothing. Ineed we could solve the problem in a stroke by giving everyone playform shoes!Graemec2 (talk) 15:07, 7 April 2008 (UTC)

Not heavy ones, though. Open-toed Stiletto heels only!Thee darcy (talk) 15:29, 24 September 2008 (UTC)

BMI normal weight range too inaccurate

the range stated now (between 18,5 and 25) is too inaccurate. An extra division is to be made:

• range 18.5 - 22.9 : good range for most people
• range 23 - 24.9 : most experts consider this a healthy range, dough there is a small increased risk of chronic disease versus the 18.5-23 category

I read the information in The Okinawa program book of Willcox, Willcox and Suzuki

KVDP (talk) 09:18, 26 March 2008 (UTC)

Please Read this notice before posting a comment Many people have addressed the fact that they themselves have been classified incorrectly by the body mass index. Please notice the fact that the body mass index is used, in clinical practice for calculating the body mass of ONLY sedentary (non active) and obese individuals (people). Please note; the actual composition of athletes or athletically-built individuals should be calculated using an amalgamation of skinfold measurements, densoiometry, or bioelectrical impedance analysis, in order to get an accurate measurement. Use common sense here; if you have developed muscle, it contributes towards your weight more than fat (it is more dense). Don't get upset if the BMI classifies you as obese; I myself weigh over 18 stones, and have less than 16% body fat and yet I am classified as obese by the Body mass index for my height. If you have any more queries, or want any advice, just leave me a message! Thanks for reading! Hope this frees up any problems you have. Otherwise, post away! The magical Spum-dandy 14:31, 4 February 2006 (UTC)

For millions of people who are not athletic the BMI is still deadly inaccurate. It's use should be outlawed. It's wrong. It's obviously wrong. You can see that just by looking at the formula.

Finnbjorn (talk) 11:54, 7 June 2009 (UTC)

What happened?

With the way to calculate it from inches and pounds?Undead Herle King (talk) 06:11, 6 April 2008 (UTC) and if ibm is not appropiate for thin individuals, what is?Undead Herle King (talk) 06:11, 6 April 2008 (UTC)

Please put new messages at the bottom, not at the top. The imperial formulae were deleted by

88.112.137.131 with the comment "this is wikipedia, not some jungle village that uses medieval units". Go ahead and restore it if you like. It's not that BMI is is inappropriate for thin individuals - it's more that it is inappropriate for shorter individuals, taller individuals, and athletic individuals. In fact, it is inapropraite for individuals (read the article.) --David from Downunder (talk) 07:16, 6 April 2008 (UTC)

input of ghandi's bmi to article

perhaps its possible to give the bmi of gandhi as a reference. He had a bmi of 17.7 As he been improving his health/diet and re-evaulating it for 35 years, this bmi may be considered a good striving point I thnik, so it may be included in the article. See Brahmacharya#Diet_and_ahimsa Also, perhaps the bmi of Brian_M._Delaney (co-founder of the CRON-diet) may be included (he's an expert on food/nutrition aswell as practitioner of healthy living aswell).

81.245.160.187 (talk) 06:33, 21 May 2008 (UTC)

Gandhi is an ascetic starving himself for fun. If my BMI was as low as 18.5, I'd be dead. Even the BMI admits that less than 18.5 is starving. Striving for a "healthy" BMI almost killed one person. This metric is wrong, and people who think that low BMIs are good are both ignorant and insane.

Finnbjorn (talk) 11:51, 7 June 2009 (UTC)

BMI formula

Could a practised hand please remove the nonsense from the formula at the head of the article - height measured in square metres (or square inches)! Elquino (talk) 13:37, 11 July 2008 (UTC)

The formula is correct; since you are dividing by the square of the height the unit is kilograms per square meter.--RDBury (talk) 13:06, 12 July 2008 (UTC)

Criticism?

Thr's criticism of the BMI, that it's outdated, that it wasn't originally intended for humans, & that if you're overweight from pure muscle, you're still concidered obese. --Preceding unsigned comment added by 67.160.77.255 (talk) 06:49, 18 November 2008 (UTC)

The athletes thing is covered. I'd love to see a source for the not intended for humans thing. Lot 49a^talk 21:10, 21 May 2009 (UTC)

your not obese if your medically healthy! that's a common misconception about obesity. your health as an athlete can actually exceed someone who has a regular bmi, in the modern age you are only called obese if you are in poor general health you can also be fat-overweight but be healthier than anyone with a regular bmi "which is purely individual" Markthemac (talk) 21:30, 7 May 2009 (UTC)

Markthemac is wrong. I was just over at the CDC website. You are obese if your BMI is 30 or higher, no matter what. You are over-weight if your BMI is 25 or higher, no matter what. This is not only absurd; it is down right dangerous. The BMI lead one individual to develop anorexia: to maintain a "healthy" BMI she had to eat no more than 800 calories and exercise at least two hours a day. It nearly killed her. This thing needs to be stopped!

Finnbjorn (talk) 11:46, 7 June 2009 (UTC)

BMI demonstration

Please view a film illustrating the BMI with expert opinion. I'd like to add it as an external link if deemed suitable. Thanks. Willsmore (talk) 15:23, 29 December 2008 (UTC)

I wouldn't include it: too flashy and annoying, doesn't add anything to what is already discussed in the article. --Steven Fruitsmaak (Reply) 15:26, 29 December 2008 (UTC)

BMI article on why it is Bogus?

• Top 10 Reasons Why The BMI Is Bogusby Keith Devlin,Weekend Edition Saturday, July 4, 2009, NPR

The BMI article is in need of correction against a reliable source. The Summary table, for example, is plainly wrong. BMI>25 is "overweight" See http://apps.who.int/bmi/index.jsp?introPage=intro_3.html —Preceding unsigned comment added by 121.79.16.1 (talk) 23:50, 7 September 2009 (UTC) = Hey! Correct the chart. It is plainly wrong. 100 kg = 220 lbs.

When calculating BMI, is the denominator figure for height in meters, feet, inches or what? —Preceding unsigned comment added by 24.96.232.171 (talk) 15:26, 27 November 2009 (UTC)

I think that the arguments made in the NPR article should be included in this article as criticism of BMI. Dreammaker182 (talk) 18:18, 31 March 2011 (UTC)

The whole formula for Body mass indexing is wrong, according to the properties of mass the correct formula should be height=inches, or meters/weight*weight*weight so your end result is a cubic number I am not a flat being. signed Robert G. Cazier Jr. a.k.a misnomer piles 01/27/2012 — Preceding unsigned comment added by 216.201.66.242 (talk) 16:10, 27 January 2012 (UTC)

Change graphs to metric ?

Hello, we're currently using imperial units here, could we change this to metric for the rest of the world or do we want to keep it US/UK centric? Most of the readership of Wikipedia I'd say is using metric and this is also an international and scientific standard. Lets keep it at that? 192.92.94.23 (talk) 12:09, 4 December 2009 (UTC)Jensen

The charts from the US CDC will be in imperial units. The top chart is in both units. Which chart are you asking about? Plastikspork _―Œ^(talk) 17:00, 4 December 2009 (UTC)

The chart is not US/UK centric, it's US centric. Can you have a chart in stones+pounds so it is understandable to us Brits? I can't do 14-times tables in my head. I'm 13 stone, not one hundred and whatever pounds. Jgharston (talk) 18:26, 27 August 2010 (UTC)

I'd say it's better to remove it than keep it in pounds and whatever. — Preceding unsigned comment added by 220.246.237.43 (talk) 16:48, 25 September 2012 (UTC)

Repeated paragraphs should be streamlined

Note that last paragraph under section Usage and last paragraph under section Limitations and shortcomings address the same topic of the appropriateness of the BMI exponent 2, whether it should be 2.3, to 2.7. Indeed, the sentences beginning However, many taller people are not just "scaled up" short people ... are identical.LoopTel (talk) 19:54, 13 June 2010 (UTC)

Mortality rates

The article says that people who are obese or underweight have a higher mortality rate than people with normal BMI, but wouldn't it depend on how underweight the people were? Also, assuming that all people die eventually, don't all people have the same mortality rate? ACEOREVIVED (talk) 15:59, 26 July 2011 (UTC)

Yes, it will obviously depend on how underweight people are and you can probably assume that people who are very underweight have higher mortality than those who are just a little. But since "underweight" also has a nice general definition, BMI<18.5, so the point there is that ALL of those people, on average, have higher mortality than all the people with "normal" BMI>18.5 and <25.

Yes. Across the entire population, at all ages, the mortality rate is 100%. (Or else someone is not telling us something.) But that's not what we're talking about here. What we're saying here is what's the mortality in say a given year of people with BMI=22 compared with BMI=32? I think you'll find the 22 people do better. That's what the article means about comparing the mortality rates. Hope this helps. Best wishes DBaK (talk) 23:25, 11 February 2012 (UTC)

Pregnancy

What changes need to be made to these guidelines to calculate BMI for a pregnant woman? — Preceding unsigned comment added by 76.181.160.60 (talk) 00:18, 11 February 2012 (UTC)

Categories

It would be nice if the categories table had weight values for an average height female as it does for a 5'11" male. — Preceding unsigned comment added by Evarlast (talk • contribs) 14:46, 23 February 2012 (UTC)

"Limitations and shortcomings"

This phrase "Because the BMI formula depends only upon weight and height, its assumptions about the distribution between lean mass and adipose tissue are not always exact." is weaselly in the extreme. Given that we are all different, the assumptions will never be EXACT. The discussions about mass being proportional to dimensions cubed, all things being equal (which they aren't) should be in this section. Sasha (talk) 09:02, 23 March 2012 (UTC)

Metrification

Should we not metrify this article? Most of the world uses metric, and feet, stones, inches, and pounds doesn't make any sense. Even less so in an article which is referencing science, which uses metric. — Preceding unsigned comment added by 84.52.200.176 (talk) 20:03, 26 August 2012 (UTC)

No, I don't see that any major change is necessary in the direction you describe; indeed I would strongly oppose such change. Most of the article is already in metric units and makes it clear that BMI is epxressed in kg/m² no matter how you calculated it. The references to feet, inches, pounds, stones etc are necessary and reasonable because in the countries in question they are the common, albeit non-medical, ways of referring to these measurements. Where they appear in this article they are mostly in conversion so they can be understood both ways. "Most of the world" may use metric units but that's not a very precise number - are you saying it's 99.9% of the world or 50.1%, and can you prove it? There are about 60 million in the UK and ~300 million in the USA of whom many still do not, in daily speech, seem routinely to use metric measures for weight and height as I understand it, so that seems like a lot of people to exclude. So, no, I don't think there is any case at all for making the article entirely metric as you seem to suggest. If there are less sweeping changes you'd like maybe you should bring them here to discuss. Best wishes DBaK (talk) 09:19, 30 August 2012 (UTC)

Feet and stones in equations seem useless in their present form

Is there any point in the presence of feet and stones in the equations near the article top, at least in their present form? These really only work with whole numbers of feet or stones, and most people are not exactly 4, 5 or 6 feet, nor exactly 9 or 12 stone or whatever. People who use those measurements might say they weigh twelve-and-a-half stone if they happen to be on the half, but if they aren't then mostly they are going to say that they are "12 stone 4" or "11 stone 3" (yeah, I wish) and that their height is 5'8" or whatever. I can't see how anyone wanting to use the equations is going to find the unconverted feet and stones useful - are they really going to bother to calculate that 5'8" is 5.667 ft, and that 12:04 is 12.286 st, so that they can plug those numbers into the equations? I really doubt it somehow - surely it is far quicker to go the other way and say that 5'8" is 68", and 12:04 is 172 lbs, and use those figures? Please note that I am absolutely not advocating that feet and stones should be omitted from the article; I use them myself and still find them useful. What I am saying, though, is that their appearance in the equations promises something it can't deliver, as they are effectively unusable there, with all due respect to those who did the praiseworthy work to get them in in the first place. I think that, yes, I would probably advocate their removal if a working substitute cannot be found; but far better would be if a way can be found (by someone cleverer than me, please) to accommodate how people actually use these units, and make them useful again. I would be very interested to hear what others think. Best wishes to all, DBaK (talk) 11:31, 13 August 2012 (UTC)

I fully agree. Decimal fractions of stones and feet are unusual. So in practice would always go to the smaller unit. Weight is 14×stones+pounds and height is 12×feet+inches. Question remains how to write this concisely in a formula? Similarly, the examples of category bounds for 1.8-metre (5 ft 11 in) person are rather useless, as well as the more extensive tabulated values (with all range boundaries duplicated). −Woodstone (talk) 15:41, 13 August 2012 (UTC)

If we can't find a way of expressing it that makes sense, I would like to suggest that the formulae involving feet and stones should be removed. I suppose it might be possible in addition to construct a very concise note pointing out that if you want to plug in these measures you need to convert them to the smaller unit first, and how to do so, but would it be worth it? DBaK (talk) 09:23, 30 August 2012 (UTC)

I've had a go along those lines. I will not go to fisticuffs to defend it, but it is a start. What do you think? (Nothing to do with the problem in hand but I also added, or tried to add, a blank line to the table to give a little separation between the lines of the equation. I had previously found this hard to read.) I'd be delighted if someone could come up with something more elegant. I remain absolutely convinced, though, that something requiring me to talk about a height of 5.667 ft and a mass of 12.286 st is just wrong. It needs either to accept input straightforwardly in st+lb and ft+in (which would be cool but fiddly to do), or only accept the simplified smaller unit, as this new version does. Comment away! :) Thanks and best wishes DBaK (talk) 11:39, 12 September 2012 (UTC)

Big categories table

What do people think of the big categories table visible here (the second table of the two immediately under "Categories")? I am not sure that, with its 96 cells, it was an enhancement to the article. It seems to go down into a depth of detail that the article otherwise doesn't use, and is arguably unnecessary when we provide external links to ways of calculating BMI. It's also a bit unfortunate that, whereas the article generally doesn't get too bound up in specific units, this has to - so to be international we would maybe also need a stones/pounds version and a metric version - another two tables the same size might overwhelm the article. I am not up for a fist fight over this, and would very much like to know what other editors think. For now, I have removed it, but only as a starting position. LBN (talk) 15:42, 19 December 2012 (UTC)

I had removed it already a while ago, but it reappeared. It duplicates information that can be obtained from the graph at the top of the article (in both metric and imperial units). It is ill-structured because it does not give the bounding values between the categories, but tries to give both an under and upper limit for each category, and in doing so leaves small gaps where the category remains undefined (and would duplicate each value if the gaps were closed). −Woodstone (talk) 07:46, 20 December 2012 (UTC)

I have removed it yet again. I have invited Nyu.empl and Nmsu.student to come and discuss it here. Best wishes LBN (talk) 02:47, 25 December 2012 (UTC)

Health consequences of overweight and obesity in adults

Does this section really belong in this article?

Clearly people with a high BMI run an increased risk of these conditions, but this information surely belongs in an article about obesity rather than one about a particular method of measuring body mass. Chuntuk (talk) 15:50, 25 April 2013 (UTC)

Power law

In Usage there is mention of (and reference to) the University of Utah maths paper on where, between 2 and 3, the correct power should be for variation of mass with height. I have found this recent article (from a blog) which, while still not an authoritative publication, discusses the issue in detail:

http://alohonyai.blogspot.co.uk/2013/09/criticism-of-body-mass-index.html

I would suggest adding some of the conclusions to Usage and providing a reference to the article.

Markelein (talk) 11:16, 28 May 2014 (UTC)

Fat Free Mass Index

(lean body mass / height squared) + 6.1 X (1.8 - H) is the formula for fat free mass index if anyone wants to chase up the link that leads nowhere. Metric measurements but it could be made work in imperial. 86.40.148.70 (talk) 16:54, 29 May 2014 (UTC)

Inaccurate topmost graphic

Hello, I thought it worth mentioning that the topmost graphic (https://upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Body_mass_index_chart.svg/593px-Body_mass_index_chart.svg.png) contains at least one significant error. I have not checked to see if it contains any other errors. I am 6'3" and 200 pounds, which comes out to a BMI of almost exactly 25, which falls on the dividing line between normal and overweight according to most sources. Therefore this dividing line should cross 6'3" at the 200 pound mark on the chart. However, it crosses 6'3" at 190 pounds. That is a 10 pound offset. I have not checked the chart for other inaccuracies, but I thought I would mention this one in case an interested person wants to further examine the graphic for correctness.

BlakeJGL (talk) 22:49, 22 May 2014 (UTC)

The graphic is not incorrect, however it *is* confusing for people measuring in pounds. To clarify, using BlakeJGL's example, the 190lbs mark is the small tick mark to the left of the longer vertical line. That long vertical line is the 90kg = 198lbs mark -- and that's where the BMI=25 dividing line should (and does) cross the 1.9m (6'3") line. Perhaps the figure would be improved by not using 20lbs small tics, and instead just labeling the 10kg lines with the appropriate values in pounds? HyperBlazer (talk) 12:41, 23 August 2014 (UTC)

BMI Measuring Machines

Nearby grocery store has a machine next to the pharmacy that measures BMI amongst other things (BP, HR); it weighs you, asks age, sex, etc, ie enough to do a table lookup. But it also has hand grips with electrical contacts, implying that it measures resistance/impedance across a meaningful frequency range, to measure the body fat directly. Or maybe its just a pulse detector ? — Preceding unsigned comment added by 98.245.49.47 (talk) 20:38, 15 September 2014 (UTC)

Waist-to-height ratio in lead

Recently a sentence was added to the lead:

Recent studies have shown that the waist-to-height ratio (WHtR) measurement is a better simple predictor of potential health conditions and outperforms other indices including BMI.

Although it may be valuable to have such a statement in a paragraph on comparison to other measures, in my opinion it does not belong in the lead. Do we prominently state in the lead in articles on most sportsmen who is the world champion in their field? Or in the lead for a medicin, another one that can treat some of the indications better? This article is about BMI, not its competitors. The lead should explain what it is and its main uses. The lead does not claim that BMI is a good (let alone the best) predictor of longevity. Somewhere in the body further analysis may find a place. −Woodstone (talk) 07:20, 14 December 2014 (UTC)

• Agree BakerStMD T|C 18:26, 14 December 2014 (UTC)

Your comparison with sportsmen is irrelevant. The problem I have with the lead is that it buys into the common understanding that BMI is the only simple measure of the issues which it has to deal with. As other comments on this talk page show, it's far from an ideal measure. It's not dimensionless, it doesn't directly work for children and it has a mediocre correlation with the problems it's assumed to be a predictor for: obesity, propensity for heart disease, diabetes etc. The only hint in the lead is the reference to "a range of perceived limitations and problems with the BMI". I'll maybe accept it's not the place to draw judgments since there isn't a widely agreed alternative, but it should at least draw attention to the fact that it is only one of a number of such simple measures and that specialists do not agree about them. Chris55 (talk) 10:49, 14 December 2014 (UTC)

New Body mass index

Body mass has nothing to do with height, rather it is the combination of fat, muscle and bone in a body. I'm a dweeb, so can't remember the name of the Greek who immersed himself in water and discovered the concept of body mass index. (along with some other hardly worthy of notice equations that are also used today.) The water displacement tool is somewhat cumbersome so people--being who they are--decided to go with the completely inaccurate but MUCH easier to do height/weight rule. These days the water displacement tool has been "ahem... displaced" by a tool that uses electricity to measure % of the three in the body. I've seen all three of them at work and I still consider a piece of paper that has not touched my body or in any way notices my ratio of Twinkies to exercise to be the stupidest idea ever considered. (by the way, that last sentence has been proven but apocryphal evidence is worse than no evidence.)deepsack (talk) 07:22, 18 August 2014 (UTC)

I think you're thinking of Archimedes with the water-displacement bit. Displacement is a measure of volume, which is related to weight by density, but volume is not included in BMI. Volume is correlated to height, but not perfectly, as more than just height goes into determining volume. BakerStMD T|C 18:30, 14 December 2014 (UTC)

It ignores basic scaling laws

"it ignores basic scaling laws whereby mass increases to the 3rd power of linear dimensions" : Indeed! But in what strange medical world are we in to keep using something ridiculous like that ? — Preceding unsigned comment added by 144.85.157.254 (talk) 23:06, 15 June 2014 (UTC)

• Disagree. Pointing out the mathematical relationships between weight and height is an important part of explaining the shortcomings of BMI as a metric on which health decisions are based. It is appropriate to include it in the section on shortcomings, where it is currently. BakerStMD T|C 18:36, 14 December 2014 (UTC)

Clarification on height

My problem with the Body Mass Index is that I have shrunk four inches since I was twenty. Do I use the height I am now (5'8"), or the height I was more than 20 years ago (5'11.75")? I have never been able to track this down, and even my doctor was uncertain. Almost all my family have shrunk with age, and it is common enough in the general population to be a significant factor in BMI calculation. Jgharston (talk) 18:22, 27 August 2010 (UTC)

Why would you even think of using the height that you were 20 years ago? (Except to make the BMI number lower, that is). You're measuring your weight as it is today, and you want to know your BMI as it is today, so why wouldn't you use your height as it is today? Chuntuk (talk) 13:26, 4 September 2013 (UTC)

@Jgharston, your BMI changes when your height changes. So your BMI is different now based on your current height than it was 20 years ago based on a different height. BakerStMD T|C 18:46, 14 December 2014 (UTC)

Average BMI calculated from average weight and height

A recent addition states:

"Researchers ... calculated the average BMI ... using UN data on population, WHO estimates of global weight, and mean height ... ."

The cited source has a similar formulation. Clearly this is nonsense. The average BMI cannot be calculated from average weight and average height. The section should be removed. −Woodstone (talk) 08:08, 14 July 2012 (UTC)

• Agree. BakerStMD T|C 18:45, 14 December 2014 (UTC)

Thank you very much for the response. A computer crash just deprived the universe of my long reply. This was probably a very good thing. Very much shorter version: I don't know enough to argue this properly; it would appear that you do; no-one else has come out to play! I suggest that, if you wish, you remove the offending bit (again: sorry) and see if it attracts further interest. WP:BRD and all that. Cheers, DBaK (talk) 07:18, 17 July 2012 (UTC)

Just saw your removal of the table. I don't see why it is not possible to calculate BMI that way. As the BBC is regarded as a reliable source, I'll restore the table. cmɢʟee☎✉ 11:24, 31 July 2012 (UTC)

@User:cmglee, I believe the correct way to determine the average BMI for a group is to compute the BMI for the individual members of the group, then average the BMIs together. This will result in a different value than if you take the average height and average weight for the group and perform the BMI calculation on the average height and weight, because the relationship between height and weight are not the same for every person in the group. BakerStMD T|C 18:44, 14 December 2014 (UTC)

After doing this experiment, I'm now convinced that it's not possible to calculate average BMI from average mass and average height. So what do you do if a reputable source makes an error? Excluding it completely seems a drastic measure. How about adding a note that the calculation may be erroneous? cmɢʟee⎆τaʟκ 12:24, 16 December 2014 (UTC)

I like it, cmglee. Can we maybe let the WHO know? They're just people too. But for now I'd prefer excluding it. No reason to propagate erroneous information. Maybe we could replace it with a mention that the BMIs of the averages (wrong) is different from the average of the BMIs (Correct).BakerStMD T|C 21:14, 16 December 2014 (UTC)

I'm totally bollixed by the BMI definition. For the last 50 years I've been thinking it was the ratio of fat to muscle mass and that the only real way to measure it was through water immersion. I'd been taught that the height/weight chart was just a cheat sheet for the real (and complicated to administer) thing. deepsack (talk) 05:27, 5 January 2013 (UTC)

Global statistics

What value or insight does the "Global statistics" table contribute to the article?

WP:INDISCRIMINATE Wikipedia is not an indiscriminate collection of information

--Nbauman (talk) 17:40, 12 April 2014 (UTC)

• Agree The table just clutters up the page and should be deleted. BakerStMD T|C 18:32, 14 December 2014 (UTC)
• The table data it is not supported by provided link. Also it clutters up the page. I removed it. Please provide WP:RS if you want to keep it. Innab (talk) 14:05, 12 May 2015 (UTC)

Problem with graphic

Obesity and BMI

The caption under the normal case is "25 < kg/m² ", which could lead someone to think 25 is the lower bound. It should say "< 25 kg/m² ". (Also, I get the vague feeling that something's missing from the graphic!) Loraof (talk) 14:55, 6 January 2016 (UTC)

Definitely the formula in the graphic is wrong. Not the unit "m", but the "height" should be squared.−Woodstone (talk) 16:18, 6 January 2016 (UTC)

I edited the image, changed to <25. Tom Ruen (talk) 23:29, 8 February 2016 (UTC)

Better, but you forgot to correct the displayed formula: height (m²) should be (height (m))². −Woodstone (talk) 08:17, 9 February 2016 (UTC)

Forms of weight and height

This article says Body Mass Index is defined as Body Mass divided by the square of body height. Perhaps it could clarify that this means weight in kilograms divided by the square of height in metres, so as to avoid confusion with imperial measures. Vorbee (talk) 08:32, 18 August 2017 (UTC)

Please read the second half of the sentence. −Woodstone (talk) 06:53, 19 August 2017 (UTC)

Untitled

What does a woman look like in such a graphic? 117.202.49.30 (talk) 12:25, 5 September 2017 (UTC)archive

Ignores variation in physical characteristics

I thought that this section was in part poorly worded but I do not enough about the background to change it. As the previous section addresses the issue of height only taken to the second exponent (resulting in an upwards bias in the result for tall people), I take it that this section does not refer to height, so any reference to 'tall' and 'short' stature in this section seems wrong. I take it, it rather refers to build, e.g. broad vs slender, thus the proportion between height and width. But in the text it all seems a bit mixed up... 2601:280:4B00:590D:B108:F377:4E31:3B80 (talk) 20:48, 3 June 2019 (UTC)

Defining formula

Currently the defining formula is stated as:

$\mathrm {BMI}$	$={\frac {{\text{mass}}({\text{kg}})}{\left({\text{height}}({\text{m}})\right)^{2}}}$
	$={\frac {{\text{mass}}({\text{lb}})}{\left({\text{height}}({\text{in}})\right)^{2}}}\times 703$ †

The way units are indicated is rather sloppy. Formally correct would be:

$\mathrm {BMI}$	$={\frac {{\text{mass}}/{\text{kg}}}{\left({\text{height}}/{\text{m}}\right)^{2}}}\ {\text{kg}}/{\text{m}}^{2}$
	$={\frac {{\text{mass}}/{\text{lb}}}{\left({\text{height}}/{\text{in}}\right)^{2}}}\times 703\ {\text{kg}}/{\text{m}}^{2}$ †

This shows a dimensionless number times the unit it is expressed in. Would this form be too confusing for the average reader? Any better proposals? −Woodstone (talk) 08:22, 17 June 2013 (UTC)

Though strictly correct, BMI is not typically specified with units, as in http://www.nhs.uk/bmi and http://www.nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc.htm so may lead to confusion unless specifically pointed out. cmɢʟee୯ ͡° ̮د ͡° ੭ 18:37, 18 June 2013 (UTC)

How is this not right?

5 ft, 8 in = 1.7272 m 220 lb = 100 kg

BMI in English measure 220 lb/(66 in ^2)=.0505

BMI in metric 100kg/(1.7272 m^2)=33.52083

BMI metric/BMI English = 704.5469

T Ashley --15:55, 6 August 2013 (UTC)65.88.43.2 (talk)

BMI in English measure 220 lb * 703/(68 in ^2)= 33.44 Omitting the 703 imperial adjustment changes everything 86.40.148.70 (talk) 16:58, 29 May 2014 (UTC)

If you measure your height in metres and your mass in kilograms, then divide the measured mass in kilograms by the square of the measured height in metres, they you will always get the right value. Then you don't have to worry if it is 702 or 703 or 704 or who cares? English measure is not designed to be exact, just to give Luddites a warm and fuzzy feel. — Preceding unsigned comment added by 174.69.64.122 (talk) 15:44, 4 January 2015 (UTC)

As pointed out above, 1 lb = 2.2 kg is an exact equation. Similarly, 1 in = 2.54 cm is an exact equation. So the conversion factor is 10000/(2.2 x 2.54²) = 10000/14.19352 exactly. This is approximately 704.54686, and not 703. Writing 700 would have been acceptable, but if we are going to give three digit accuracy then this should be 705, and not 703. I care, and am changing this.
Arif Zaman (talk) 05:04, 25 December 2018 (UTC)

The conversion factor would need a fix. I'm going to demonstrate this using the previous example.

Example

5'8'' = 5 ft + 8 in / 12 in/ft = 8 in + 5 ft * 12 in/ft = 5.67' = 68'' = 1.73 m
220.4623 lb * 0.4536 kg/lb = 100 kg

International System
100 kg / 1.73 m² = 33.4 kg/m²

USA System
220.4623 lb / 68² in² = 0.0477 lb/in²

Conversion factor
33.4 kg/m² / 0.0477 lb/in² = 700.2096 ≈ 700

--Morbius (talk) 16:43, 1 December 2019 (UTC)

By calculating this way, using an example, you are stacking rounding errors. The official definitions are 1 lb = 0.453 592 37 kg and 1 in = 0.0254 m. If you redo the calculation with these numbers you will find a conversion factor of 703.069579639…, which rounds within reasonable accuracy for this measure to 703. −Woodstone (talk) 04:35, 2 December 2019 (UTC)

Using a greater accuracy for the input data is as useless as much boring exercise for 2 reasons: 1) the final result is affected by an error not greater than its accuracy; 2) four decimal digits are more than enough for the accuracy wanted. So the right conversion factor is still around 700 and not 703 for the accuraccy of 1 unit we all want. Try to demonstrate your thesis computing your long numbers, not by words, please. --Morbius (talk) 19:08, 3 December 2019 (UTC)

As your changing example shows, calculating the conversion by rounding in examples is not reliable. And your statement above that "1 lb = 2.2 kg is an exact equation" is invalid. The exact number is 1 lb = 0.453 592 37 kg. The correct calculation goes as follows:

1 lb / in² = 1 (0.453 592 37 kg) / (0.0254 m)²=(0.453 592 37) / (0.0254)² kg / m² ≈ 703 kg / m².

Rounding further to 700 would change a BMI of 25 to about 24.9 kg / m² and is an error larger than acceptable for usually reported values.

−Woodstone (talk) 05:41, 4 December 2019 (UTC)

It's OK now but I never said those statements about pounds (lb). Read carefully! Arif Zaman said them. If you had checked my computations you would have seen that I used the conversion factor 0.4536 kg/lb; so I know what 1 pound is respect to kilograms! Bye. --Morbius (talk) 23:45, 4 December 2019 (UTC)

And don't say I "changed" my example please: I only adjusted the style once! My calculations were right; the method a little less. --Morbius (talk) 06:09, 5 December 2019 (UTC)

By the way your dimensional analysis is not correct, Woodstone. If 1 lb/in² = x (0.453 592 37 kg) / 0.0254 m² where x is the wanted conversion factor so x is expressed by the measurement unit [lb/in²] / [kg/m²]. The measurement unit you used for the conversion factor is rather the one used for the BMI! --Morbius (talk) 08:05, 5 December 2019 (UTC)

Multiplying by 1 does not alter the result. The x in your proposal is 1. Look at the first and last expression in the chain:

1 lb / in² ≈ 703 kg / m²

The conversion pops out automatically. −Woodstone (talk) 10:19, 5 December 2019 (UTC)

OH, MY BAD! It's 1 lb/in² / ((0.453 592 37 kg) / 0.0254 m²) = x ≈ 703, so x != 1. Your dimensional analysis IS WRONG! I already know that 1 is the neutreal element for the multiplication but why should we care about it?! The measurement unit for the conversion factor is [lb/in²] / [kg/m²] or, if you prefer, [lb/in²] * [m²/kg]. BMI is expressed by [kg / m²], not the conversion factor! --79.13.22.134 (talk) 17:38, 5 December 2019 (UTC)

Sorry, Woodstone! I got it. In my example x is just a simple factor, the same of the left equation member, that is 1.
So 1 lb/in² ≈ 703 Kg/m². Pardon! --Morbius (talk) 18:51, 6 December 2019 (UTC)

Damn! 1 lb/in² ≈ 703 * 1 Kg/m² => 1 lb/in² / 1 Kg/m² ≈ 703. So conversion factor has no dimension! I was wrong. Sorry. — Preceding unsigned comment added by Morbius (talk • contribs) 21:44, 6 December 2019 (UTC)

Underweight also increases death

Hello, the article says that overweight increases death risks but underweight also increase death risks so I recently tried to add content with a reference stating that but it was reverted https://en.wikipedia.org/w/index.php?title=Body_mass_index&type=revision&diff=933937173&oldid=933629446 . I would be pleased to help improving the article with such information Valerie Nurse (talk) 23:42, 3 January 2020 (UTC)

Here is the text I would like to include in section 'Relationship to health', I would be happy if anybody could improve the text : According to some studies, adults who are underweight have higher risk of death Valerie Nurse (talk) 16:34, 4 January 2020 (UTC)

References

Scalability nonsense

The 'Scalability' and 'Scaling' sections contain some total nonsense and need to either be deleted or replaced with something that is actually scientific. They say stuff like "mass scales naturally with the cube of the height" and "mass increases to the third power of linear dimensions" -- which is completely wrong and nonsense. People are not symmetrical water balloons or cubes, they are complex biomechanical organisms. - http://www.bio.miami.edu/tom/courses/bil160/bil160goods/17_scaling.html "the body plan must change as the size of an organism increases". - https://en.wikipedia.org/wiki/Allometry#Isometric_scaling_and_geometric_similarity - https://en.wikipedia.org/wiki/Square%E2%80%93cube_law#Biomechanics

Actual data about the precise exponents do exist, and they are clearly less than cubic, and quite close to square for weight (but higher for bone mass). - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2729090/ "Weight, primary lean components (SM, residual mass, AT-free mass, and fat-free mass), and liver scaled to height with powers of ≈2 (all P < 0.001); bone and bone mineral mass scaled to height with powers 2.31–2.48" DKEdwards (talk) 02:51, 17 February 2021 (UTC)