The finding that normal-weight people don't outlive their overweight peers had comedians calling for second helpings of mashed potatoes when it was released a few years ago. Researchers from the Centers for Disease Control and Prevention based their analysis on the well-respected National Health and Nutrition Examination Survey. "The findings really should not have been such a surprise," says Katherine Flegal, Ph.D., the study's lead author. Indeed, more than a dozen other large studies have found either no difference or a slightly lower mortality rate among the moderately overweight.

Other experts, however, have reached different conclusions. They point, for example, to two large studies published in the New England Journal of Medicine in 2006. One, of over 1.2 million Korean men and women, found that mortality risk began to increase even in those who were only moderately overweight. The other, an analysis of more than 500,000 members of AARP, had similar findings.

But with time comes perspective. The researchers still point to differences in study design, but say that their findings match on a few key issues: