Talk:Body mass index

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, densiometry, or bio-electrical 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)

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

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 fuck 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)

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.

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.

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)

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.

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. [2] Peachy1 20:33, 20 January 2006 (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

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)

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)

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)

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)

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

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" [3]. 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)

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

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 [4]. 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. I don't want to make an edit this big without some input, though. Opinions?24.14.40.242 23:48, 2 October 2006 (UTC)