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January 02, 2013

Being Slightly Overweight May Reduce Risk of Dying

by Jessica Berman

People who are slightly overweight or mildly obese have a lower risk of early death than normal weight individuals, according to a new analysis of nearly 100 international studies.

The studies, most conducted within the past decade, included about three million adults from around the world.  A collective analysis of these studies by researchers at the National Center for Health Statistics in Maryland, part of the U.S. Centers for Disease Control and Prevention, reveals that slightly overweight or obese individuals were six percent less likely to die from all causes compared to people of normal weight.  But the researchers found that severely obese individuals were still at a 30 percent greater risk of death compared to healthy-weight individuals.

The analysis involved studies conducted in the U.S., Canada, China,Taiwan, Brazil, India and Mexico.

Study lead author Katherine Flegal says she was not surprised that overweight people would not have a higher death risk.

"Because we'd actually already read a lot of this literature and realized that [mortality rates for] overweight would be at least not higher than normal weight," she said.  "I guess I was a little bit surprised that it was definitely lower.  And I was also surprised that the lower rates of obesity didn't seem to differ from normal weight."

But Flegal stresses the difference in mortality rates appear to be small between normal-weight people and overweight and mildly obese individuals.

The finding by Flegal and colleagues have raised new questions about the reliability of the so-called "body mass index" or BMI, a measurement of body fat as a ratio of height to weight, that has been promoted in recent years by public health experts as a barometer of potential health risks.

Steven Heymsfield, executive director of the Pennington Biomedical Research Center in Baton Rouge, Louisiana, says a fit individual may be perfectly healthy but might weigh more because of extra muscle mass.

“It's very common in the military, for example, where you have young men and women who are very physically fit - their BMI can be a little higher.  And so the military knows that and they check that with body fat measurement if they exceed the BMI guidelines," Heymsfield said.

But Heymsfield cautions that individuals should not conclude that it's okay to put on extra kilograms, since being at a healthy weight lowers the risk for heart disease and diabetes.

An article by the CDC's Katherine Flegal and colleagues, and an accompanying editorial by Steven Heymsfield, are published in the Journal of the American Medical Association.