Body fat determines need for weight loss

By Joene Hendry

NEW YORK (Reuters Health) - Measuring body fat, rather than body mass index, appears to more accurately identify people who need lifestyle interventions to lose weight, study findings suggest.

Excess body fat is a risk factor for many major health problems such as heart disease and diabetes, researchers note in the Nutrition Journal.

When evaluating individuals for lifestyle recommendations to minimize such health risks, body mass index (BMI) under identifies risk, said Dr. Ottavia Colombo of the University of Pavia in Italy.

"The use of BMI alone does not discriminate between fat mass and fat-free mass, nor reflect the fat mass distribution," Colombo told Reuters Health.

Colombo and colleagues recruited 23 men and 40 women, aged 20 to 65 years, to undergo body composition analysis in the Human Nutrition and Eating Disorders Research Centre at the university. The volunteers were healthy, but led sedentary lives and were not following a low-calorie diet.

The researchers obtained each person's BMI as well as body-fat measurements including waist circumference and total percent body fat. The also calculated a measurement similar to BMI that identifies fat mass called body fat mass index. The investigators then compared the percentage of the study group that would be told to lose weight according to each calculation.

BMI calculations, they found, identified 11 percent of the group as needing strong recommendations to lose weight and 41 percent as needing basic recommendations to lose weight. By contrast, waist circumference measurements indicated about 25 percent would need strong recommendations to shed pounds and 36 percent would need basic weight loss recommendations, Colombo said.

Moreover, 29 percent and 48 percent would have received similar weight loss recommendations according to total percent body fat measurements, while 21 percent and 54 percent would receive the same, according to body fat mass index.

"Using criteria based on body adiposity (fatness) rather than body weight would result in a much greater proportion of the study population receiving recommendations for weight loss," Colombo said.

Studies that focus on changes in body fat among larger groups of people recommended for lifestyle change, might better identify which body fat index is most clinically relevant, the investigators say.

SOURCE: Nutrition Journal 2008.