Body Fat Measurement: Percentage Vs. Body Mass

What's the best measurement to assess health risks from being overweight? Experts say BMI and body-fat percentage both have their place

By John Casey
WebMD Weight Loss Clinic - Feature

Reviewed By Michael Smith, MD

Weight, body fat, body mass index -- what do all these numbers mean? And what do they really tell you about your health?

Some experts tout BMI, or body mass index, as the most accurate way to determine the effect of weight on your health. In fact, most recent medical research uses BMI as an indicator of someone's health status and disease risk.

The CDC provides the following ranges for BMI values for adults:

Underweight Less than 18.5
Recommended 18.6 to 24.9
Overweight 25.0 to 29.9
Obese 30 or greater

But others feel that body-fat percentage is really the way to go.

"The BMI numbers are way too general to be really useful," says Tammy Callahan, marketing manager of Life Measurement Inc., which manufactures a fat analyzer for use in gymnasiums and medical settings. "These numbers were developed using data from enormous numbers of people. They don't tell you anything about your own body composition, how much of your weight is fat, and how much is muscles and tissue."

But don't throw out that BMI chart just yet.

Are You At Risk?

"I'm not against people using devices to figure out fat percentages, but it is a well established fact that your BMI number does tell you a lot about your risk of diseases, especially heart disease and diabetes," says Harry DuVal, PhD, associate professor of exercise science at the University of Georgia in Athens. "Fat percentages just don't have enough research behind them yet to tell you how much risk of disease you face."