According to a new study in the Journal of the American Medical Association, being a little overweight may reduce the risk of dying in a given period.
Katherine Flegal of Americas Centres for Disease Control and Prevention, examined about 100 studies of more than 2.9m people and 270,000 deaths.
Being overweight is defined as having a BMI between 25 and 30.
People with a BMI of 30 or more are considered obese.
Dr Flegal and her colleagues observed that obesity was associated with a higher risk of mortality in a given study period.
Those with chronic diseases such as diabetes and heart conditions seem to show an inverse relationship between BMI and mortality.
The overweight receive life-prolonging medical care, such as treatment for diabetes and drugs to control heart conditions.
The body may use fat tissue to mop up excess lipids caused by overeating.
These chemicals, which include fats, are needed in small amounts to make cell membranes.
But when fat tissue becomes overloaded, the hypothesis goes, those lipids wreak havoc on other parts of the body.
More body fat therefore constitutes of a better use.