An anonymous reader writes to mention that while a couple of years ago researchers found that overweight people have a lower death rate
than people with a normal weight, it may be more complicated
than that. "Now, investigating further, they found out which diseases are more likely to lead to death in each weight group. Linking, for the first time, causes of death to specific weights, they report that overweight people have a lower death rate because they are much less likely to die from a grab bag of diseases that includes Alzheimer's and Parkinson's, infections and lung disease. And that lower risk is not counteracted by increased risks of dying from any other disease, including cancer, diabetes or heart disease."