Body Fat Measurement: Percentage Vs. Body Mass (cont.)

"What we want people to shoot for is a range rather than a magic number," says Barbara J. Moore, PhD, president of Shape Up! America. "It's comforting to know that women can be and should be fatter than men. They have a totally different reproduction function and the higher fat in women supports that reproductive function."

But not all measures of fat percentage are equal. Some methods have high error rates. The two most common methods used are skin-fold measurement and bioelectrical impedence analysis

In skin-fold measurement, a trained specialist uses calipers to measure specific spots on the body. These measurements are compared to a chart that estimates fat percentage. You may have seen this used in your gym or doctor's office. These skin-fold devices can also be purchased and used at home. However, the accuracy of this method varies greatly based on the user's abilities. Bioelectrical impedance analysis, the other common method, is the technology behind the many fat percentage scales sold for home use.

"The error rates for these can be as high as 8%, plus or minus," says DuVal. "Other methods are highly accurate but much more complicated, like X-ray analysis, water displacement, and others. That's why BMI has its place in weight management. It may be crude, but it does give you a good idea of risk quickly and easily."

DuVal says that fat-percentage measurement, despite the inaccuracies, can be useful.

"In terms of ease-of-use and usefulness, the BMI can't be beat," he says. "But if a home, fat-measurement device helps someone stay focused on their diet and exercise level and motivated to stay healthy, then I think the device has a place in weight management."

Published Nov. 25, 2002.

SOURCES: Centers for Disease Control and Prevention American Council on Exercise Tammy Callahan, marketing manager, Life Measurement Inc. Harry DuVal, PhD, associate professor of exercise science, University of Georgia American Journal of Clinical Nutrition, September 2000 Barbara J. Moore, PhD, president of Shape Up! America.

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