A few weeks later, that very study was refuted by CDC director Dr. Julie Gerberding. "We have had a dramatic increase in the proportion of people in our world that have obesity," she said in a news conference. "That constitutes, in my view, a serious epidemic."

Gerberding indicated the problem with the study was with the way causes of death are officially reported. "Obesity is not listed on death records," she explained. "We have to rely on extrapolations." And that, she implied, is why it appeared that someone a bit zaftig might appear to live longer than someone within normal weight guidelines.

So, if we assume the CDC statistics were nothing more than a glitch, is it better to be underweight? There's some evidence that skinnier species of some animals live longer. Scientists have found that they can lengthen the lifespan of rats by a third by cutting their calorie consumption by 30 to 40 percent. Cutting a rat's food in half, though, does not offer the same life-lengthening benefits.

And that's not all. The link between less food and longer life "seems to be generally true in many species," says Lenny Guarante, professor of biology at the Massachusetts Institute of Technology and a specialist in aging. It's not entirely clear whether caloric restriction works in humans too, although some research suggests it's possible. The first human studies of the effects of CR are now underway at several institutions.