In January 2013 a study looking at the relationship between body weight and mortality rates got lots of press, and for good reason. It was published in the Journal of the American Medical Association (JAMA).
The researchers, from the Centers for Disease Control and Prevention (CDC) and elsewhere, pooled data from 97 studies done in more than a dozen countries, totaling nearly 3 million people. The surprising results: Overweight people were found to have a 6 percent lower overall death rate than people of “normal” weight. The data were adjusted for age, gender and smoking.
And while moderately or severely obese people were 29 percent more likely to die during a given period, the mildly obese were at no greater risk than normal-weight people. For people over 65, the mortality benefit of carrying some extra pounds seemed to be most notable.
Research on this subject has produced mixed results. This was not the first analysis to indicate that being overweight may be the “sweet spot” on the weight spectrum, especially for older people, but it is the largest and most rigorous study so far.
Commentators had a field day with the news, lambasting “overzealous” health experts who’ve warned about the dangers of the obesity epidemic. In contrast, others worried that junk-food companies would use the study to encourage consumers to forget about weight control and healthy eating.
But the picture is not black and white. Before you stock up on ice cream and doughnuts and cancel your gym membership, it’s important to look at the bigger picture.
Defining weight categories
First of all, what is normal, overweight or obese? That, of course, is the crux of the matter. The JAMA study used standard ranges based on body mass index, or BMI. About one-third of Americans are overweight, one-third obese and one-third normal weight or underweight, by these definitions.
BMI is calculated by dividing weight (in kilograms) by height (in meters) squared. Here’s an easier way to compute it: Multiply your weight (in pounds) by 705; divide the result by your height (in inches); then divide again by your height. This government website will compute your BMI for you.