BMI and BAI: Better fitness through fancy math

by Denis Faye | March 4, 2011

Next to Monsanto, fad diets, and trucker hats, BMI (Body Mass Index) is the bane of my existence. It’s commonly used by the medical profession – even taught in schools – to determine how fat you are. Yet, it can be obnoxiously inaccurate. Here’s the calculation:
First off, I don’t see why you need to add a bunch of math to your weight and height. No matter how many numbers you multiply it by, it’s still your weight and height. Making it fancy doesn’t make it more accurate, Pointdexter. Furthermore, it doesn’t account for muscle mass or bone structure, so it’s usually completely wrong. According to BMI numbers, Arnold Schwarzenegger (BMI 33), Sylvester Stallone (BMI 34) and Dwayne “The Rock” Johnson (BMI 33) are all fat.

I’m 5’11” and 165 pounds, putting me at a BMI of 23, which is on the large side of normal. But the thing is, I’m big boned – and I don’t mean that in a fat-sitcom-dad-justifying-his-gut way. I have broad shoulders and a wide rib cage. I also have approximately 9% body fat, which, according to the American Council on Exercise, is “athletic” or, in layman’s terms, “really skinny.” The two don’t match.

So I guess someone important somewhere finally figured this out. According to WebMD, new research in the journal Obesity is testing a new method called the Body Adiposity Index (BAI) that’s supposed to be more accurate. (Not to be confused with Chinese actress Bai Ling, who continues to be very inaccurate.) The new method measures height and hip circumference and, to make it extra special, features even fancier math.

BAI = (hip/height x the square root of height) minus 18.

Or, in other words, the hip measurement in centimeters divided by the height in meters times the square root of height minus 18.

Square root! It must be accurate. It’s about time someone factored square roots into a body fat calculator!

There’s been a lot of interesting research lately about hip circumference and obesity, but why all the arithmetic and acronyms? And what about the whole apple v. pear-shaped body issue? Look, I’m not a doctor, I don’t even play one on television, but I know a fat person when I see one. You want me to tell you if you need to lose weight or not? Strip down to your undies and let me have a look. I’ll tell it to you straight. No math or co-pay necessary.

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5 thoughts on “BMI and BAI: Better fitness through fancy math

  1. marijka

    How about the theory that your waist should be less than half your height? So if I’m 64″, my waist should measure 32″ or less, which is quite proportional. Any opinions?

  2. D Faye

    I don’t know. I guess it’s better then a bunch of pointless math, but again, there are a lot of squat, fit people. Two people the same height can have very different waists and still both be fit!


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