The study found that people who are a little overweight at age 40 live six to seven years longer than very thin people. Very thin people have life expectancy that is less by approximately five years than the life expectancy of obese people.

Shinichi Kuriyama, an associate professor at Tohoku University's Graduate School of Medicine who worked on the long-term study of middle-aged and elderly people said, "We found skinny people run the highest risk... "We had expected thin people would show the shortest life expectancy but didn't expect the difference to be this large".

The study was conducted by a health ministry team led by Tohoku University professor Ichiro Tsuji. It included 50,000 people between the ages of 40 and 79 for a period of 12 years. It was conducted in the northern Japanese prefecture of Miyagi. Kuriyama said, "There had been an argument that thin people's lives are short because many of them are sick or smoke. But the difference was almost unchanged even when we eliminated these factors". He added that the main reasons for the shorter life spans of skinny people were believed to include their heightened vulnerability to diseases such as pneumonia and the fragility of their blood vessels.

But Kuriyama warned he was not recommending people eat as much as they want.