The Folly of BMI (Bad Measurement Instrument)

ScaleHave you ever had a doctor or nutritionist or some stranger on the street calculate your BMI? In my previous post, I indicated that I would be exploring some of the sources of guidance we might draw upon since the Bible is so woefully negligent in telling us anything about just how much meat we can carry around on our frames. Today, I’d like to explore BMI or Body Mass Index.

Developed by Adolphe Quetelet, a Belgian scientist (but not physician), in the first half of the 19th century, BMI was an attempt to describe the relative heaviness of people. In the metric system, you take the weight (mass) of the person in kilograms and divide by the square of the person’s height in meters. To use English measurements, we divide the person’s weight in pounds by the height in inches (squared) and then multiply by 703. There the formula looks like this:

BMI = (pounds/inches²)x703

In my case, it would be worked out like this for my current weight of 190 and height of 5′ 11″.

26.49=(190/71*71)x703

My BMI of 26.49 places me pretty solidly in the overweight classification, which ranges from 25 to 30. In order to reach the top of the “normal (healthy weight)” range, I’d have to drop another 12 pounds, reaching 178.

In reality, at present, I could probably stand to lose at least 5 and maybe 10 pounds, but I hardly feel as if such loss is essential. I would agree that getting myself to 178 might have me in the “healthy weight” range, I feel confident that such a loss isn’t necessary to barely reach an acceptable place.

What is wrong with BMI? Plenty. Let me give a simple case study. Omar Infante is the 2nd baseman for the Kansas City Royals. His height is listed as identical to mine, 5’11”. His weight is 195. Therefore Infante has a BMI of 27.2, considerably higher than mine. Are you going to suggest that I have a healthier body composition than this man who is able to deftly turn double plays at a major-league level? Look at any photo of Infante and you’ll have to agree that he’s not the pudgy designated hitter body type. Does he seem healthy? Obviously.

BMI measures one thing, height vs. weight. It does not take into account the frame size of the individual. Somebody with an even higher BMI than Omar Infante is basketball star Lebron James, who comes in at 27.4. Is Lebron overweight? Hardly. He’s a big man and carries a lot of muscle. BMI does not distinguish between good weight and bad weight. It makes no distinction between muscle and fat.

I’m hardly the first to note the measurement’s flaws, but despite years of such criticism, BMI is still widely used, mostly, I would guess, because it is so simple to calculate.

Quetelet was a sociologist, not a physician. His interest was in populations rather than individuals. If you take BMI measurements for a few hundred people in Cleveland and a few hundred people in Nairobi, there might be some useful conclusions to draw from the findings. But BMI is not a terribly useful measurement for individuals, except that it provides doctors with a club to wield on their heavier patients: “Well, your BMI of 30.3 indicates that you are obese!”

To measure individuals using such a population-oriented tool is somewhat like measuring the sin of an individual in comparison with a population. If my SMI (Sin Massiveness Index) is low enough in comparison to those around me, then I can just go into maintenance mode, right? And if my SMI is higher than those around me, then I should feel like a terrible person. Have you ever been in a church where people seemed a bit complacent with their SMI? Or met people who felt unworthy of their church because of their particular SMI? That’s no way to think about your holiness. BMI, while not quite so poor a measurement, is wrong in a similar way.

 

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