If you were asked to visualize a model of longevity, would you picture someone overweight? Probably not. However, new research suggests that people who carry extra pounds could have a lower all-cause mortality risk than normal-weight people.
In a study published in the Journal of the American Medical Association (2013; 309 , 71–82), researchers measured body mass index in 2.88 million people. The goal was “to perform a systematic review of reported hazard ratios of all-cause mortality for overweight and obesity relative to normal weight in the general population,” the authors explained.
They classified BMI into five categories: overweight (BMI of 25<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30<35), grades 2 and 3 obesity (BMI of ≥35) and normal weight (BMI of 18.5<25).
Compared with normal weight, obesity (all grades combined) was associated with an 18% higher risk of all-cause mortality. That increased to a 29% higher risk for grades 2 and 3 obesity. On average, however, the overweight group had a 6% lower risk of mortality than the normal-weight group. And those in the grade 1 obesity group had a 5% lower risk than those in the normal-weight group.
“Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality,” the authors reported. However, “grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.”
The authors did not look into why overweight and slightly obese people had lower mortality rates than normal-weight individuals.
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