December 2, 2009

The dangers of BMI and bureaucracy

Contentious debate has characterized the decision of Lincoln University to force students with a body mass index of 30 or above to take a mandatory fitness class in order to graduate. Some argue that it is discriminatory; some question the validity of the assumptions underlying the policy; and some feel that it is too intrusive and paternalistic of the college to interfere in a student's life in this way. Here I would like to address the biggest flaw in the program, which also is a major shortcoming of other college health policies: the assumption that body mass index is an accurate indication of a person's health.

Body mass index (BMI) was developed between 1830 and 1850 by Adolphe Quetelet, a Belgian astronomer, mathematician, statistician and sociologist.

Note that his education, while extensive, does not include nutritional or physiological training. Furthermore, nutrition and physiology at the time were woefully underdescribed and not well understood. Even he never intended BMI to be used as a diagnostic criterion for individuals; he calculated it as a measure of the "average man" in the society of his contemporaries.

Even though it is widely acknowledged that BMI is a quite inaccurate measure of body fat for many subgroups of the population (such as men, the elderly, non-sedentary and tall people), it is still widely used by the misinformed (or lazy) because it is perceived as some kind of a magical number. Any nutritionist worth her salt will tell you that BMI is absolutely not to be used as a diagnostic criterion for individual cases. The formula for BMI takes into account only height and weight. (It is, by the way, a completely arbitrary calculation of weight divided by height squared -- which has no medical provenance.) It ignores the critically important factors of body composition and frame size. For instance: A very muscular, fit athlete with low body fat will most likely be labeled obese by the BMI system, and a perfectly healthy, tall person will probably be labeled underweight. BMI does not allow for people who are genetically tall and slim; it predicts incorrectly that tall people are simply scaled-up versions of short people, when the reality is that tall folks have a slimmer build relative to their height than shorter people. Similarly, it cannot distinguish between dense muscle tissue and adipose tissue -- as far as BMI calculations can show, weight is weight. Someone with a height of 5'6" and a weight of 150 lbs with 5% body fat would have the same BMI of someone with the same measurements but 20% body fat. See a problem there?

According to Dr. Jon Robison, an adjunct assistant professor at Michigan State,

"The BMI is relatively useless as an indicator of health for individuals. ... [T]here is a minimal relationship between increased BMI and health-related issues, except at the very extremes of the weight distribution (very, very fat and very, very thin)."

Okay, so BMI is good at telling you, "Hey, you're really fat" or "Damn, you look like a twig." But chances are, you could see that impressionistically -- people at the extremes of the scale look like they are at the extremes of the scale. So why do we need BMI? Why do people even keep using it?

Because it's easy. Accurate measures of health -- such as DEXA scans, waist-to-hip ratio, and other measures of body composition -- are too time-consuming or complex to be easily adopted. BMI is a quick and dirty calculation, requiring no thought or effort. It lets administrations (in this case, college bureaucrats) ignore the fact that individuals are, in fact, individuals, with varying needs and unique circumstances. From a bureaucratic standpoint, treating students like actual, distinct human beings is very, very messy, and highly inconvenient. Easier to pretend that they all fit the nice, neat (albeit wildly inaccurate) formula for BMI, and judge them that way.

Obviously, BMI alone is an extremely poor measure of health. There are numerous clubs nationwide for "Clydesdales" and "Athenas." These are runners and triathletes over 200 lbs (for men) and over 145 lbs (for women). Obviously you have to be in top physical condition to do triathlons and run marathons. These people haven't been impeded by being "overweight," and I would wager that their blood pressure, cholesterol levels, etc. are much healthier than the men and women with lower BMIs who are sedentary.

On the flip side, there have been multiple cases of colleges resisting a student's return to campus after a medical leave because their BMI was not high enough. I am aware of such cases occurring at NYU and, yes, Dartmouth, as well as other universities. In each case, women with eating disorders (notably anorexia nervosa and bulimia nervosa) took medical leaves to recover, and in each case, the college bureaucracy deemed that they were not fit to return to college work because their BMIs were too low. Never mind that the women's doctors, therapists, and psychiatrists had unequivocally declared that recovery had happened, and that the women were healthy and able to return to college life. No, because the BMI was not just so according to the college bureaucracy, these women were inhibited from continuing with their lives. Keep in mind that the people making the decision to allow or prevent a student from returning to study have not treated the student in any medical capacity and are therefore not capable of judging the best course of action. This is a prime example of the damage that can be done by applying BMI to individual cases. Healthy people end up with their lives in turmoil simply because they don't fit an outdated, inaccurate, nonsensical equation developed by a Belgian man over 150 years ago.

Leaving a student's life and health in the hands of an overburdened bureaucracy will inevitably result in innumerable wrong decisions. A bureaucracy is incapable of caring about individuals or treating them with the personal concern which is vital to effective healthcare. Thus, they adopt slipshod diagnostics -- like BMI -- to make life-altering decisions for students. This is highly alarming and unethical.

A system like Dartmouth's, in which every student must fulfill a number of physical education requirements in order to graduate, is far more appropriate than dictating that each student have an "acceptable" BMI. It should be clear by now that BMI is a very dangerous benchmark by which to judge whether a person's body is acceptable.


  1. Anonymous8:15 AM

    5'5" and 180 lb. = BMI of 30
    5'11" and 215 lb. = BMI of 30

    BMI is not the only indication of a person's health but it does provide some valuable information about body fatness for most people.

  2. Actually, the BMI predicts that 1 of the other 2 of our 3 dimensions will increase with proportionally with height. It predicts that the third dimension does not change. As a result, BMI generally underpredicts the weight of very tall people.