Could a few extra pounds mean fewer years of life?
Today's Washington Post describes the results of two studies being published in this week's New England Journal of Medicine. One is a study of 500,000 US adults, the other is a study of 1 million Korean adults. Both of these studies show that being overweight is associated with a risk of dying prematurely.
The US study found that moderately overweight 50-71 year olds are 20 to 40% more likely to die in the next decade compared to their normal weight peers. The story goes on to state that skeptics remain unconvinced...they say that "the analysis is flawed and will alarm people unnecessarily." One skeptic, Glenn A. Gaesser of the University of Virginia, is quoted as saying "I think they are just adding to the obesity hysteria...It's not as bad as they make it seem."
What is going on here? Why are these studies and others that purport to show an impact of obesity on lifespan so controversial. First of all, they are epidemiologic studies. By design, they can demonstrate associations, but they can't prove cause and effect relationships. That means that they can show that shorter lifespans and heavier weights occur more frequently in certain people than others. It does not mean that overweight causes shorter lifespan. Perhaps something else caused both things to happen in same people. In other words, something else is really the root cause.
There is good evidence to suggest that, in fact, that is the case. If you examine statistics about risk factors for the leading causes of death in obese people, such cardiovascular diseases, you find that not all obese people develop these complications. What seems to separate overweight/obese people with those complications from obese people who do not develop them is whether they become significantly insulin resistant when they gain weight.
It is possible that it is only obese insulin resistant individuals that are at risk of early death from heart attacks, strokes, and diabetes. Obese individuals who maintain insulin sensitivity may have more normal lifespans. The middle ground in the debate over overweight and obesity and lifespan may be that some people -- those who are insulin resistant -- are at risk and others, those with normal insulin sensitivity, are not.
Instead of continuing to argue that "all obesity is bad" or "obesity is not all that bad," we should look more closely at the data to determine if there are some easily identifiable subsets of the population who will have devastating health consequences when they gain weight. Let's take this debate to the next level so we can get on with the serious business of promoting health in this country.