Better to Be Fat and Fit Than Skinny and Unfit

But the most striking finding was that fitness level, regardless of body mass index, was the strongest predictor of mortality risk. Those with the lowest level of fitness, as measured on treadmill tests, were four times as likely to die during the 12-year study than those with the highest level of fitness. Even those who had just a minimal level of fitness had half the risk of dying compared with those who were least fit.

 http://www.nytimes.com/2008/08/19/health/19well.html?em