Friday, January 20, 2006

The Body Mass Index (BMI) Is Wrong

1. The Body Mass Index (BMI) Is wrong because the "weight" is expressed as a function of the square of the height. That might be ok if we had two dimensional bodies, height and depth or height and width. In fact, we have three dimensional bodies: height, width and depth. Therefore "weight" must be expressed as a function of the cube of the height. This problem is a biggie. Fortunately, it can easily be dealt with by changing the mathematical formula.

2. Another problem is that even if the problem defined above is solved the density of the body is simply not considered. Even the cube formula does not really deal with weight. It deals with volume. That would be ok if all of us had equal density. Maybe we do. I just don't know.

I recognized the first problem about 8 years ago and derived an appropriate cube formula. I did not attempt to publish it because I have no credentials in the health field and because I fully expected that a mathematically literate MD would promptly shoot down the BMI humbug. As far as I know, this never happened.

Eight years have passed and it seems that BMI is well established. Recently, I observed a BMI chart in the examination room of my primary care physician. I asked him, "Doctor, does it not seem to you that the BMI weights recommended for short people are excessive?" The good doctor looked at the chart, thought about it and said, "Yes, they are a bit on the heavy side."

See for yourself. Google BMI and click on any of the listed items. Health Monitor table is easier to read than the others.

If you would like to see my cube function chart, e-mail me at and I'll put it up.


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