
Chapter 15. 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 the 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 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. http://www.healthmonitor.com/BMI.htm Health Monitor table is easier to read
than the others.
Three exhibits will help to demonstrate the square based BMI fallacy:
15.1 displays BMI data under the old square formula
15.2 displays BMI data under the correct cube formula
15.3 presents the difference between the two tables.
This Page was last update:
Friday, February 3, 2006 at 6:43:52 PM
This page was originally posted: 1/20/2006; 8:49:04 PM.
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