It's important to note that in Japan, people with a BMI starting at 25 are considered obese, whereas by United States standards, a BMI of 30 is considered obese. Therefore, the Japanese researchers stress that trying to extend one's life by putting on some extra weight is not a good idea.

Furthermore, they speculate that one reason thinner people have shorter lives may have to do with smoking habits, as smoking tends to keep weight down in many people. Shorter life spans of skinner people may also be due to their heightened vulnerability to such diseases as pneumonia and the fragility of their blood vessels, notes Shinichi Kuriyama, associate professor at Tohoku University's Graduate School of Medicine, who worked on the study. He cautioned that he was not recommending people eat as much as they want. "It's better that thin people try to gain normal weight, but we doubt it's good for people of normal physique to put on more fat," he says.