Doctor Calls Bullshit On The BMI

Illustration for article titled Doctor Calls Bullshit On The BMI

Three years after noted "Fat-O-Sphere" writer Kate Harding posted a slideshow illustrating how ridiculous the BMI standards are, the NY Times agrees: the body mass index is unreliable.

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In our society, we're so quick to call someone who appears to be fat "unhealthy." But health is not a quality that can be judged or seen with the naked eye. There are thin people who smoke and don't eat any vegetables. There are obese people — including Steven N. Blair, one of the nation's leading experts on the health benefits of exercise — who jog every day. You can't see genetic material, a decaying liver or gingivitis in a photograph.

The BMI — which is calculated by dividing your weight in kilograms by the square of your height in meters, doesn't differentiate between fat and muscle. Dr. Carl Lavie, a cardiologist at the Ochsner Heart and Vascular Institute in New Orleans, tells the Times that according to the BMI: "a six-foot, 250-pound man will be obese." But! "If he were an N.F.L. lineman of 6-foot-3 weighing 280 pounds, he might be solid muscle with only 2 percent body fat."

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Basically, trying to judge the health of an individual using the BMI? It's bullshit. To make matters worse, there's what Dr. Lavie and colleagues have called "the obesity paradox."

The paradox refers to the repeated finding that while overweight people are more prone to heart failure, patients with heart failure have lower mortality rates if they are obese. The reason for this paradox is far from clear, though Dr. Lavie suggested that one explanation could be that once people become ill, having more bodily "reserve" could be to their advantage.

In many cases, fat has benefits. But the chance that this science will stop folks from calling overweight people unhealthy? Slim.

Weight Index Doesn't Tell the Whole Truth [NY Times]
Related: BMI Project [Shapely Prose]

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DISCUSSION

clothandcake-old
clothandcake

Sigh. The argument presented in this article is nothing new. It outlines the primary limitation of the BMI system (which we have all been aware of for years) and involves the same old requisite components:

(1) A focus on outliers (usually represented by either Arnold Schwarzenegger, or here, a football player), rather than on the overall utility of the measure for the majority of the population.

(2) Supportive reference to Dr. Blair or another proponent of the "fit-but-fat" hypothesis. Dr. Blair is well-respected, but there are many other similarly respected obesity scientists who have a somewhat different and equally valid perspective. Those opposing viewpoints need to be represented here in order to provide balanced information to the reader.

And, as always, this article ignores the fact that an imperfect measure is not the same thing as a useless measure. BMI is imperfect. It is also very useful, and astonishingly predictive in many contexts. It's a basic guideline. Look, folks who actually use BMI (e.g., health researchers) don't walk around pretending it's the gold standard of health. It's a cheap, easy proxy measure of adiposity. Of course it's not as accurate as an objective measure of body fatness (e.g., a DEXA scan), but it can be used in many situations where direct observation would be impossible.

As much as I love Jezebel, it seems to be generally incapable of sensible reporting when it comes to the study of weight and health. The articles posted here tend to be defensive and based on a poor understanding of the intent or reality of this field of research. It's just a bunch of rallying around the idea that obesity is not, in general, detrimental to health, without any rigorous or critical examination of that notion. There is an excessive focus on the existence of exceptions (e.g., "so-and-so is clinically obese, yet healthy") paired with a complete disregard for the important population-level health impacts of obesity.

I just feel irate that a blog seemingly devoted to critical examination of our culture is willing to contribute to the widespread misinterpretation of public health science. There is no need for the constant conflation of obesity research and fat discrimination. We can acknowledge that, on a population level, obesity is harmful, while also working to end fat discrimination and understanding that there are exceptions to every rule. Is that SO hard?!?