Is Being Overweight Healthy? The New JAMA Study

Is being overweight healthy?

I actually spoke with Dr. Katherine Flegal yesterday. She's the lead researcher on the JAMA study that got so much media attention; the one that made it seem like fat people are healthier than normal weight people and that they live longer. Seems the media didn't get the whole story.

What a surprise.

Here's what Dr. Flegal and her colleagues did find. Number one: Compared to the number of deaths in a control population of "normal" weight people (BMI 18.5-25), being underweight (less than 18.5) was associated with about 33,000 more deaths than would be expected in the "normal" weight group. Number two: Being obese (BMI >30) was associated with about 111,000 more deaths. So being in either one of these categories is a risk factor.

It was the "middle" category that was puzzling. The federal gov't definition of obesity begins at a BMI of 30 and defines "overweight" as 25 through 29. And, yes, the people in this category actually had somewhat fewer deaths than those of normal weight.

This did not in any way mean they were healthier. Dr. Flegal was very clear that no one should draw that conclusion from her study — in fact, she and her team didn't even look at measures of health. They just looked at one outcome: dying.

So people who were moderately overweight could be expected to die at a slightly lower rate than "normal" weight people. There are lots of possible explanations for this. One of them is what I call the "Arnold Phenomena." Remember, the BMI does not, repeat not, take into account body composition. Any bodybuilder or athlete who has single digit bodyfat and a ton of muscle will fall into the "overweight" BMI classification. So there's an awful lot of highly conditioned people in that classification. Maybe they skewed the results.

Or maybe people in that category — which is about 40% of America — are just smarter about getting good medical care.

Another possibility — one that Dr. Flegal suggested — is that maybe that extra fat or weight serves as a kind of nutritional or strength reserve in times of stress. Maybe it serves as a kind of "cushion" to help survive the stress of something like cancer or cancer treatement. Who knows?

Point is, we really don't know why those folks die at a slightly reduced rate from normal folks.

It's important to remember that any association study never tells us anything about cause and effect. It only tells us that two things are found together. Sometimes one causes the other, but just as often it doesn't. It's human nature to think that when things happen at the same time, one causes the other (like thunder and rain, or a wearing a lucky shirt when you pitch the winning game.) DVD sales and diabetes both went up during the same time period and therefore there's a statistical correlation between them, but there's no cause and effect relationship.

I know that an awful lot of columnists were celebrating this study with undisguised glee (David Brooks of the NY Times, for example.) I'm just not at all sure that the take home message from this study should be to stop worrying about weight because fat people are healthier.

That's certainly not what the author of the study said, and it's probably not the best message to walk away with.