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Why the BMI is harmful BS

Panic! Last March, the McAllen-Edinburg metro area was deemed the most obese, comprised of almost 40 percent fatties, apparently, according to the Gallup-Healthways poll. That same poll is referenced in Jose S. De Leon III’s article on Valley food.

Problem is, the buzzword of the decade, obesity, is not just bad science, it’s not medical science at all.

A person is classified as obese based off the Body Mass Index; that slanty rainbow chart in the doctor’s office that compares a person’s height and weight.

And that formula, the BMI, was carefully calculated and tested on several different body types by scientists and dieticians with many titles following their names, right? No.

BMI’s maiden name is the Quetelet Index, after Belgian mathematician and sociologist Adolphe Quetelet. Right,  mathematician, not physician. What’s more, it dates to 1835, and accompanied Quetelet’s theory on the “average man”, which obviously is very useful for speculating on general populations. Not so much for the lone patient in a doctor’s office, though.

In fact, Quetelet did leave the world a bit of guidance on how to use his formula. Specifically, he mentioned a small caveat – don’t use it to assess individual health. And…
the United States uses BMI to assess health, and even worse, an individual’s health.

The BMI chart breaks people down into four basic groups: underweight, normal, overweight and obese. And to Quetelet’s credit, his wonky formula comparing two picked-at-random human traights actually does work, most of the time. That is, square a person’s height and compare it to weight and you will, in most cases, be able to tell how much adipose tissue they’re carrying around.

But not always. Classified as overweight by the BMI are both basketballer Yao Ming and soccer player Abby Wambach. And that’s the problem, the BMI’s logic is faulty. See, a person with a high percentage of fat will have a high BMI, but a person with a high BMI does not necessarily have a high percentage of fat. It’s the old square and rectangle riddle.

So, yeah it’s misleading, but how is it harmful? For starters, in the 1970’s, health insurance companies cast about for a way to determine health and longetivity using easy to gather data about people. They landed on the 100-year-old, bumbling BMI as the standard. As a result, a higher BMI will now net a higher premium, at least 25 percent more expensive, generally. Remember when the BMI was never supposed to be used for individuals? Yeah.

Even worse, much of the country thinks that makes sense, because using the BMI to calculate general health leads to an even more dangerous assumption: that health is totally dependent on weight. It isn’t and it never has been. Sure, the amount of fat in a body definitely has some relation to overall health, but it is far from the only factor. Additionally, Quetelet’s notion of the “average man” is useful in his fields of mathematics and sociology, but very harmful in medicine. There is no magic ratio of height and weight that makes a body healthy. Saying that there is and that healthy and unhealthy can be separated for everyone by decimal points on a multi-colored chart is beyond ridiculous.

As long as the Valley and the country as a whole continue to be distracted by its “obesity epidemic,” the real issue of health will get lost in the mess. It’s time to start thinking of medical health as involving the whole person, and not just their waists.

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