The review, of 97 studies that included a combined 2.88 million people, questions the notion that people of normal weight live longest.
“It is possible that under certain circumstances, being a little overweight is good as opposed to bad,” says Steven B. Heymsfield, MD, executive director of the Pennington Biomedical Research Center in Baton Rouge, La. Heymsfield wrote an editorial on the review but was not involved in the research.
About 30% of women and 40% of men in the U.S. are overweight based on their body mass index (BMI), a measure of size that takes into account a person’s height and weight.
While they may not be able to wear their favorite clothing size, Heymsfield says it doesn’t necessarily mean they are sicker than people who are at so-called normal BMIs.
“You have to separate out the cosmetic part from the health part,” he says.
The review, which is published in the Journal of the American Medical Association, takes a fresh look at nearly two decades of research into the relationship between body weight and death risk.
“We have a huge amount of data because we collected almost 100 studies,” says researcher Katherine Flegal, PhD, a distinguished consultant with the CDC’s National Center for Health Statistics in Bethesda, Md.
People with BMIs under 30 but above normal were less likely to die during the studies compared to people with normal BMIs.
A reduction in the risk of death from all causes was about 6% lower for people who were overweight, and it was remarkably consistent from study to study, Flegal says.
Those people considered obese based on BMI, however, were worse off. They were about 18% more likely to die of any cause compared to those of normal weights.
Research Comes With Caveats
Though the findings are provocative, they come with some important caveats.
The study only looked at the association between death and body size. It didn’t include other measures of health that may be related to weight.
“Total mortality [death from all causes] is important, but it doesn’t tell you much about quality of life,” says Heymsfield. “It’s not whether you’re at risk of developing diabetes. It’s not whether you’re at risk for developing joint problems."
The study also just shows an association; it doesn’t prove that body weight is the reason that some bigger people tended to live longer than those at normal weights.
For that reason, Flegal says, people shouldn’t give up on their goals to eat right and exercise.
“We’re not trying to make any recommendations,” she says. “It’s not intended as a call to any kind of action.”
But the findings may be reassuring to people who carry some extra weight but are otherwise healthy.
“Maybe a few extra pounds is not as lethal as we’ve been led to believe,” Heymsfield says.