While the obese or underweight are at greater risk of death, people marginally overweight have longer lifespans than those considered to be of "healthy" weight, researchers claim.
The findings defy the commonly held belief that staying slim is the secret to healthy and long life. Scientists examined the relationship between body mass index and death among 11,326 adults in Canada over a 12-year period. They discovered that underweight people were 70 per cent more likely than people of normal weight to die, and extremely obese people were 36 per cent more likely to die.
However, modestly overweight individuals were 17 per cent less likely to die, the study showed. The relative risk for obese people was nearly the same as for people of normal weight, the report concluded.
Commenting on the findings, David Feeny from the Kaiser Permanente Center for Health Research, said: "It's not surprising that extreme underweight and extreme obesity increase the risk of dying. But it is surprising that carrying a little extra weight may give people a longevity advantage."
However, the researchers also warned people of normal weight not to try to put on extra pounds in the hope of improving their health.