Too much emphasis on BMI and other norms

Frances Chan is a history major at Yale University who has been involved in a struggle with that university’s health services because they kept telling her that at 92 lbs, she was too thin and that her Body Mass Index was too low. Her height is 5’2″, which gives her a BMI score of 16.8 while the ‘normal’ is in the range 18.5-25.

She wrote in an article that the Yale health center people said that her health was at risk, and that she had to eat more and build up her weight and she had to have mandatory weekly weigh-ins and meetings with a clinician. It did not seem to matter that she told them that all her family was thin and that she had always been thin but healthy. She tried to gain weight by stuffing herself with ice cream and cookies and reducing her physical activity but gained only a couple of pounds. After a struggle with the university, they finally agreed to stop bugging her.

I have found that in the US people worry a lot about norms for all manner of things and treat them as prescriptive, worrying far too much if they slip out of the supposedly right range. Parents are perhaps the most guilty of this, especially when their children are young.

The Chan story struck a chord with me because our older daughter was tall for her age and thin too, but active and healthy. Her school nurses would say that she was too thin and that she should gain weight, although they did not pester her like what happened to Chan. The situation was not improved when my younger daughter told her friends in school that her older sister was anorexic. She was surprised at the reaction her statement received because she had not realized that being able to use both hands was such a big deal. What had happened was that she had confused the word ‘anorexic’ with ‘ambidextrous’, which is what her older sister is!

Fortunately for us we could laugh about these things because our children’s pediatrician had told us all along that our children were healthy and to ignore those who said they were too thin. He said that since her parents were both very thin, our daughter’s physique was not unexpected. He said that people made a fetish about the BMI, not recognizing that it is just one piece of data and that one should look at the overall health instead.


  1. Scott D says

    Isn’t the BMI a poor standard for individual’s anyway? it was my understanding (without googling it) that BMI applies to large populations of people and is not necessarily a good measure for individuals. Even between ethnic groups, don’t the “normals” vary?

    It would seem to me that the best measure in terms of health would be % Body Fat, which would tell a person how much of their weight is lean body mass vs. fat. The only problem (for institutions and corporations) is that is harder to measure percent body fat than it is to get a BMI number.

    I think people use BMI because it’s a lazy way to categorize people. All you need is a height and a weight. It’s easy for institutions and actuaries to use BMI , but I don’t think it is necessarily that helpful for the individual as they try to manage their health.

    By either measure I need to reduce my body mass.

    Excuse me while I go run the stairs.


  2. M says

    The BMI is a very poor scale. It doesn’t distinguish muscle mass and other things, and it when you get outside of a range it doesn’t work for shorter people or taller people either. Heck, even bone density can cause a problem, my bones are very dense which add to my weight, and while it’s great that they don’t break easily, being said to be overweight when your not, even just to look at me I’m not, but some formula thinks I am is rather annoying. If you also examine the history, somewhere in the early 90s they changed the percentages and suddenly people who were considered normal were suddenly overweight overnight, just because of pressures by insurance companies.

  3. says

    I wrote a blog posting on DA here, about the history of BMI.

    TL;DR, it’s complete pseudo-science. Basically, someone fit Adolphe Quetelet’s poll of his friends who he thought were ideally built to a formula and called it an ideal.

    I am not saying that it’s a bad idea to have some kind of objective idea of what’s a healthy weight/fat percentage, etc. I am, however, saying that pulling a bunch of numbers of your ass like Quetelet did and then torturing people based on them – as so often happens – is a bad idea. If there is such a thing as a healthy weight, then medicine ought to be trying to figure out how to quantify it by some means that is better than BMI.

  4. Trickster Goddess says

    One thing that always irked me is that the formula for BMI doesn’t make sense mathematically. The result gives a ratio of mass to area; mass being a 3-dimensional measure while area is 2-dimensional measure. Even worse, the square meters in the equation isn’t even a true 2-dimensional product, such as h x w. It is merely a 1-dimensional measure (h) multiplied by itself.

    So in reality, the BMI provides the nonsensical measure of “pounds per inch” or “kilograms per metre”.

  5. TxSkeptic says

    I’ve always thought BMI was crap. I’ve long had a scale that (supposedly) measures body fat percentage. Whether the scale accurately does it or not is another question, but I think the concept is much more sound as a measure of a healthy weight metric. Through the years and various workout and diet phases, I’ve seen these measurements make more sense than BMI, like increasing weight & lower fat% in early workout phases, leading to lowering of both as the program progressed. Also, lowering weight and stable or increasing fat% on diets without an accompanying exercise routine.

  6. Matt G says

    I remember hearing years ago about a method of estimating % body fat which involved pinching and measuring skin in three (?) places. You want to have a convenient (1) way to – as accurately as possible – estimate (2) some parameter (3) that correlates with health (4) (e.g., likelihood of developing cancer, heart disease, etc.). That’s a tall order.

  7. smrnda says

    I’ve always thought these measurements existed as an easy way to (mostly) tell people they were fat, or the other way around here, and that they have very little meaning.

    I actually don’t weigh myself, so I don’t know what any of my numbers are. Long ago I decided to avoid that just so it’s a number I won’t think about.

  8. karmacat says

    I working with eating disorder patients, so reading about her wt and height was alarming. But there are other factors that go into determining someone’s “ideal” weight. You can look at the person’s weight/height growth chart. You can also look at someone’s forearms. Check certain lab tests can show that a person is getting enough nutrition. Although a person can have normal labs tests and be anorexic.

  9. karmacat says

    I read her article. It doesn’t say if she saw an eating disorder specialist, but it certainly shows that she got more than enough labs and info from her pediatrician. I may have had her eat one meal in front of me. People with anorexia tend to have obsessive eating practices and have a hard time eating in front of others. It does sound like they got too obsessed with that one measure.

  10. says

    BMI is about as useful for health measurement as “double and add thirty” is for converting celsius to fahrenheit. It’s only valid within a very small range of possibilities.

    The two most importatn numbers are, and always have been, resting heart rate and blood pressure (diastolic and systolic). If either is too high or too low, it’s a sign of poor circulation (e.g. cholesterol and blockages) or lack of fitness.

  11. dysomniak "They are unanimous in their hate for me, and I welcome their hatred!" says

    I may have had her eat one meal in front of me.

    Why? And on what grounds? Is she your child? Your pet? What right do you or any doctor have to demand she perform for you?

    Seriously the arrogance and paternalism of so-called “healthcare” professionals is staggering.

  12. karmacat says

    I said “may.” I certainly wouldn’t stick her for labs 3 times. When you see people dying from not eating, it is really hard not to be paternalistic. The other issue is that the sooner you can diagnose and treat an eating disorder, the more likely the person will recover. Some people who have anorexia will do anything to hide that they are not eating. Anorexia has the highest mortality and morbidity of any mental illness. I would rather be a little too paternalistic than have a patient die. Dysomniak, I don’t what else say to you. You have the right to ask questions but as soon as you call someone names and make generalizations you have shut down the discussion.

  13. dysomniak "They are unanimous in their hate for me, and I welcome their hatred!" says

    And how about the mortality and morbidity of people not seeking medical care at all, or going to quack homeopaths because every single time they walk into a doctor’s office they have to deal with authoritarian creeps like you who treat them like they’re cattle being prepared for slaughter? How about the all the people who kill themselves because of the routine abuse and dehumanization of the psychiatric industry?

    For fuck’s sake she isn’t even that skinny.

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