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BMI not the best body fat measure

Apr 10th, 2012
Staff Writer

BMI not accurateBody Mass Index has long been considered the key number used to determine healthy body weight. But research suggests that the 180-year-old BMI system may not be accurate enough.

In a study, researchers found the formula may incorrectly classify more than half of all women and 20% of all men as having normal weight when, in reality, they carry an unhealthy proportion of body fat.

The study, published in the journal PLoS One, used a sophisticated imaging technology to measure body fat and compared the findings to BMI scores. The difference in the imaging and BMI scores suggests many more Americans are overweight or obese than is currently thought, said the lead author of the study Dr. Nirav R. Shah, New York State commissioner of health.

"The Healthy People 2010 goal was to reduce rates of obesity from 23% in 1988 to 1994 to the target of 15%," the authors wrote. "Not only was this goal unmet, but in light of this data we may be much further behind than we thought."

Imaging to assess obesity is much too expensive to conduct on everyone, experts say, and methods other than BMI are needed. One possible solution is to measure the hormone leptin, which is secreted by fat and circulates in the bloodstream. Researchers found leptin levels correlated closely with the obesity scores obtained by imaging technology. Another alternative is to alter the BMI chart to match reality. For example, while a BMI of 25 is considered overweight in women, that threshold should probably be lowered to 24, the authors said.

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