Is The BMI (Body Mass Index) A Flawed Method For Measuring Health?

In the fitness community, mention of the BMI (Body Mass Index) is usually met with rolling eyes, obscene hand gestures, and the occasional charlie horse. We just can’t understand why such a flawed system is in place to gather information about someone’s health. But, not everyone is a part of the lifting community. Many people, (including physicians, and well-meaning coaches) still use the BMI to measure someone’s health.

To understand the BMI, first we have to take a look at its history.

The History Of The BMI

In the early 19th century, the BMI was introduced by a Belgian named Lambert Adolphe Jacques Quetelet. He was a mathematician (Note: not a physician) who produced the formula to give a quick and easy way to measure the degree of obesity of a general population to assist the government in allocating resources. His project was intended to define the “normal man”. He never intended the equation (weight equals height squared) to be used to determine body fat. Even though the equation was largely ignored by the medical community, insurance companies began using somewhat vague comparisons of height and weight among policy holders in the early 20th century. In 1972, the BMI caught on with researchers because it was a quick and easy way to measure societies and their obesity levels. At first the BMI was used by epidemiologists in studies of population health, but was quickly adopted by doctors who wanted a quick and easy way to measure body fat in their patients.

The head researcher who brought this about in 1972, Ancel Keyes, never intended for the BMI to be used on a individual level. In fact, his original paper warned against it because it didn’t take into account things like age, sex, muscle mass, ethnicity, etc. In fact, a review of his paper had this to say:

It’s one thing to estimate the average percent body fat for large groups with diverse builds, Keys argued, but quite another to slap a number and label on someone without regard for these factors… Now Keys’ misgivings are gaining traction across the world of medicine: BMI simply doesn’t work when it comes to individual measurements.

This brings us to a short list of reasons why the BMI is so inaccurate for measuring an individual’s health.

1. Physiologically, it’s wrong

The first obvious reason is that it makes no allowance for proportions of bone, muscle and fat in the body. Bone is more dense than muscle and twice as dense as fat, so a person with a lot of muscle and strong bones will have a high BMI. Example: Almost every athlete out there.


2. Logically, it’s wrong

The CDC says on its Web site that “the BMI is a reliable indicator of body fatness for people.” This is a fundamental error of logic. For example, if I tell you my birthday present is a bicycle, you can conclude that my present has wheels. That’s correct logic. But it does not work the other way round. If I tell you my birthday present has wheels, you cannot conclude I got a bicycle. I could have received a car. Because of how Quetelet came up with it, if a person is fat or obese, he or she will have a high BMI. But as with my birthday present, it doesn’t work the other way round. A high BMI does not mean an individual is even overweight, let alone obese. It could mean the person is fit and healthy, with very little fat.”

3. Numbers don’t lie, but liars use numbers

We have all seen the headlines: “40% of America overweight or obese”. Well how do you think they get those figures? By using the BMI. This doesn’t mean that 40% of us are waddling around like the people on the news, who they only record from the waist down. It means that could be a large percentage of that figure who are actually quite fit, but according to a 200 year old method, are “overweight or obese”. The equation also uses an air of scientific authority by having numbers 1-100, but all it really boils down to is mathematical snake oil.

4. It can adversely affect your insurance/ doctor visits

Insurance companies sometimes charge higher premiums for people with a high BMI. So if you are all muscle and healthy bone, you may have to pay for those high premiums. When doctors continually rely on the BMI, they don’t feel the need to use more scientifically sound method to measure obesity levels.

On top of everything else, with such strict BMI requirements, it is pretty embarrassing for the country when statistics are on the news regarding the health of the nation. Yes, there of course is an obesity epidemic, but is using a 200 year old method, made by someone who was not even a physician an accurate way to measure it?


Sources:

  1. Eknoyan, Garabed (January 2008). “Adolphe Quetelet (1796–1874)—the average man and indices of obesity”. Nephrol. Dial. Transplant. 23 (1): 47–51. doi:10.1093/ndt/gfm517. PMID 17890752.

  2. ^ E.g., the Body Mass Index Table from the NIH‘s NHLBI.

  3. ^ Beyond BMI: Why doctors won’t stop using an outdated measure for obesity., by Jeremy Singer-Vine, Slate.com, July 20, 2009

  4. ^ Keys, Ancel; Fidanza, F; Karvonen, MJ; Kimura, N; Taylor, HL (July 1972). “Indices of relative weight and obesity”. J Chronic Dis.. 1 25 (6): 329–343. doi:10.1016/0021-9681(72)90027-6. PMID 4650929

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