I think I first heard from Brian/BStu/Red No. 3 the observation that if a study seems to show benefits to being thin, it’s accepted at face value, but if a study seems to show benefits to being fat, it’s always questioned and people attempt to explain it away. (Also, people try to explain away studies that show disadvantages to being underweight or in the thinner half of ‘normal’.)
I think after this latest study, we can say with confidence that the conclusion that ‘overweight’ people live the longest is not going away. But people are rushing to explain it away. William Saletan runs down the list of explaining-away explanations that have been proposed.
Fat is bad for you, right? That’s what doctors tell us. But a review of nearly 100 studies, published this week in the Journal of the American Medical Association, confirms previous indications that the story is more complex. Being overweight or even mildly obese, as measured by body mass index, doesn’t make you more likely to die than a person of normal weight. It makes you slightly less likely to die.
How can this be? Is fat good for you?
That’s the wrong conclusion, according to epidemiologists. They insist that, in general, excess weight is dangerous. But then they have to explain why the mortality-to-weight correlation runs the wrong way. The result is a messy, collective scramble for excuses and explanations that can make the new data fit the old ideas. Here’s what they’ve come up with…
Interestingly, although it seems clear that Saletan isn’t too impressed with most of these explanations, the promotey-graphic-thingy at the top of Slate’s page where they put the featured stories made it look the opposite. I should have done a screen-capture of it, but IIRC it said “Do overweight people live longer? Why it’s not that simple”, or something to that effect. I’m pretty sure of the “not that simple” part, anyway.
Anyway, I can’t see any good reason to try to explain away the reduced death risk* for ‘overweight’ people but accept at face value an increased risk of death in BMIs >35 (the start of the ‘class II obesity’ category). If you accept that some BMI categories increase risk of death, I don’t think you can make exceptions for the ones you like better.
Some of the things on the list aren’t even examples of explaining the results away, though; they’re admissions that being ‘overweight’ does lower your risk of death.
4. The dangers of being underweight hide the dangers of being overweight. A JAMA editorial notes that people in the thinner half of the “normal” BMI range have a higher mortality rate than those in the plumper half. This thinner subset inflates the normal-weight group’s mortality rate, which makes the mortality rate among overweight and obese people look good by comparison. The solution is to shift the whole scale to the right, so that these thin people are recognized as underweight, while people presently labeled overweight are redefined as normal weight. Once we’ve completed this reallocation, it will be clear once again that overweight people—now defined to include many whose BMI would previously have put them in the obese category—are at higher risk of death than the newly reclassified normal-weight people are. The value of weight control will be reaffirmed, but the thresholds will have changed.
So, the result is still that people with a BMI between 25 and 30 are at a low risk of death compared to those with a ‘normal’ BMI.
7. Fat protects you against injury. Many old people die from falls. Chubbier people “have more padding to protect the bones should a patient take a tumble, lowering the risk of a life-endangering hip fracture,” notes the Los Angeles Times.
Once again, this does nothing to contradict the finding that people with a BMI between 25 and 30 are at a low risk of death. This only supports the idea that being in the ‘overweight’ category is good for you. I don’t see any reason to decide that diseases for which obesity is a risk factor ‘count’ but diseases for which obesity lowers the risk don’t.
*Yeah, I know, “risk of death” sounds weird given that everyone is at a 100% risk of death eventually. What it means is the risk of dying within a specific time period–whatever time period a particular study is looking at.