Dr Flegal told The Independent she had decided to conduct a second, larger, study on the same theme to counter the sceptics. She and her team examined results from 100 studies from around the world, involving three million people and 270,000 deaths.
The results are published in the respected Journal of the American Medical Association, which also published the earlier study. They show only the severely obese, with a body mass index above 35, have a significantly increased mortality, up by 29 per cent. Otherwise, extra weight appears to be protective. Underweight people, meanwhile, have a 10 per cent higher rate of premature death than those of normal size, according to earlier research. "There is already a lot of literature showing that overweight is linked with lower mortality," said Dr Flegal. "It is not an unusual finding. But authors tend to shy away from it. They tend to underplay it or try to explain it away."