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Are Normal-Weight Americans "Over-Fat?"

November 22, 2010

 

Recent data from a nation-wide survey of 13,000 American adults shows that Americans with normal BMIs may be “over-fat” compared to other populations and earlier generations, says Marie-Pierre St-Onge, PhD, assistant professor of medicine in the Institute of Human Nutrition, in a commentary published in the Nov. issue of the journal Obesity.

The data, originally published last year by researchers at the CDC, show that among Americans with BMIs below 25, women have an average body fat percentage of 34 percent and men have an average body fat percentage of 23 percent. In contrast, Europeans at a normal BMI have much lower body fat percentages – 25 percent for women and 18 percent for men – according to a small study of Swiss adults. (A BMI between 18.5 and 24.9 is considered normal).

“These are surprisingly high percentages, especially for people with normal BMIs,” Dr. St-Onge says. “It’s disconcerting that even the leanest Americans, those in the 5th percentile for percent body fat, have body fat percentages close to 30 percent for women and 20 percent for men.”

Dr. St-Onge adds that the numbers could send the wrong message to Americans and health professionals that the body fat percentages measured by the survey are acceptable or healthy.

“These numbers are useful if considered as a “state of the nation,” but they don’t provide any information on the desirability of such high fat percentages from a health standpoint.”

It’s still unknown, however, how much body fat is healthy. Other researchers are now analyzing the survey’s data on blood glucose, cholesterol, physical activity and other risk factors to determine the cut-off between healthy and unhealthy body fat percentages.

In the meantime, Dr. St-Onge suggests that Americans with normal BMIs shouldn’t be complacent.

“We don’t have data about healthy body fat percentages, but we do know that waist circumference is strongly associated with unhealthy metabolic risk factors,” she says. “Even people with a normal BMI can have large waists, so a tape measure is an easy gauge and a good place to start.”

Men with waists larger than 102 cm (40 inches) and women with waists larger than 88 cm (35 inches) have a greater risk of developing type 2 diabetes, high blood pressure, and cardiovascular disease.
 

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