From the article:

The government equates obesity with a body mass index, or BMI, of at least 30. Someone who is 5-feet-4 would have to weigh 175 pounds to reach that threshold.

The index is calculated by dividing a person's weight in pounds by his height in inches, squared, and multiplying that total by 703. For some people, particularly athletes who exercise a great deal, the BMI index could show them as being obese when in fact they are in excellent physical condition.


Notice it is just the SQUARE of the height. But if you scale up someone say from 5 to 6 feet the weight would go up as the CUBE of the height. Result - people that are just bigger, not fatter, have a higher BMI. There are some more sublte reasons why someone taller should actually weigh more that a scaled up version of a smaller person. (Bones have to be thicker to support the added mass).

One has to wonder why it was done this way? Perhaps because it is asking too much for people to do more than squaring a number?