From time to time I read comments or articles that are critical of judging a person’s weight by using the Body Mass Index (BMI). I have heard that there is a recent film that calls its usefulness into question. Being a physician, I thought I should clarify some of the more common misconceptions surrounding it. In my next few posts I’ll discuss some of the more common myths about the BMI and point out some facts to help you understand how it should be used and why it’s important:

Myth 1 – BMI Doesn’t Really Measure Obesity

This one is partially true. The BMI uses a person’s weight & their height to calculate a measure that best approximates a person’s bulk. Clearly weight alone is not helpful since it varies according to height. Including height tends to make BMI measures more comparable. The one big flaw is that it cannot distinguish the body composition of an individual – how much of their weight is due to fat versus muscle or bone. Consequently, a muscular weight lifter who has a low amount of body fat may have a BMI that suggests he is overweight or obese. All health care professionals are aware of this limitation and would not draw any conclusions about a person’s health based on their BMI alone. But you just have to look around to realize that most of our fellow Americans are not body builders and the odds are that an elevated BMI in an American is due to an excess amount of fat.

Bottom Line: While BMI alone isn’t a perfect measure of a person’s body fat, it gives a good approximation.Health care professionals will consider it and other measurements in assessing the proper weight range for an individual.

In my next post I’ll discuss another myth I’ve heard that the BMI really is not useful.

For Your Health – Dr. Bob