Friday, July 8, 2011

BMI is Bullshit

BMI is an inexpensive, mathematical way to determine if someone is height/weight proportionate. In order to calculate one’s BMI, divide one’s weight in pounds by one’s height in inches squared, then multiply if by the conversion factor 703 (from its European routes, needed to convert pounds to kilograms and inches to meters). Or use the handy dandy charts posted in every doctor’s office everywhere. On the surface, BMI charts are an okay model, but they discount the fact that not every person is built the same way. For instance, BMI’s do not account for age, gender, muscle mass, or body fat. So, a 25 year old 6’1” body building man weighing in at 240 pounds would calculate as obese, whereas a 86 year old 6’1” man whose bone mass is deteriorating and weighs in at 165 pounds would be considered normal. Similarly, put the same body building man against a 6’1” 240 pound man who leads a sedintary life and these two men are on the same playing field where BMI charts are concerned.
BMI’s also have only five ways of defining people: underweight, normal, overweight, obese, and morbidly obese. These words aren’t so much medical diagnoses as social constructs.

A Belgian mathematician, Adolphe Quetelet, developed what we now recognize as BMI sometime between 1830 and 1850 while he and contemporaries were creating social physics. Social physics is less glamorous than it sounds and is mostly just Quetelet’s argument that all social statistics need to revolve around mathematics. The term BMI first appeared in the Journal of Chronic Diseases in 1972. Noted American scientist, Ancel Keys, argued that this formula was appropriate for population studies, but not for individual diagnosis. This means that BMI is a relatively accurate way to categorize the lifestyles, food intakes, and diets of people within a certain height and weight range, but is entirely too general to apply to individual cases. In my humble opinion – and the opinion of several doctors and scientists – BMI is an inconsistent, flawed, and hurtful way to measure health. To make matters worse, health professionals employ a modified version of BMI on children and teens. This modified version puts America’s youth into four percentile categories used for screening future health problems related to weight. But, as we have seen, BMI cannot assess whether or not an individual will have “weight related” problems, i.e. high blood pressure, diabetes, or a weak heart, because BMI is not a predictor of potential diseases or health complications based on lifestyle.
One thing BMI charts do fabulously well, however, is to reinforce the American ideology that fat equals diseased, lazy, and out of control. Although many doctors and nutritionists are quick to defend athletes whose BMI is “too high” by stating factually that their muscle mass is not accounted for, very few people are as willing to defend the fat individual who maintains a healthy lifestyle. BMI corresponds beautifully with fat stigma and gives laymen and professionals alike another reason to say, “Get it together, fatty.”

For a visual of this prejudiced crime against science, be sure to check out Kate Harding's photo expose.

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