The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people.
There does seem to be some question, at least among the experts quoted in this story, as to whether people ranked overweight by their Body Mass Index live longer because of their weight ("There’s something about extra body fat when you’re older that is providing some reserve," says one expert) or because their weight is just causing them to have increased contact with medical professionals ("You’re more likely to be in your doctor’s office and more likely to be treated," says another expert).