Whoopsie. Just as all those New Year’s dieting resolutions are kicking in, along comes the latest salvo in the confusing obesity-mortality wars. “Oh, my,” I said this morning when I heard Harvard nutrition expert Walt Willett call this latest study a bunch of “rubbish” on NPR. “They’re playing rough.”
At issue is this simple question: Does being overweight make you die sooner, or might it actually be protective? But of course, very little is simple in the world of nutrition studies, or when links between Body Mass Index and health are concerned. Here’s the conclusion from the study, that in effect, very obese people tend to die earlier, but more mildly overweight people may tend to live a bit longer:
Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.
And here’s Walt Willett on NPR today:
“This study is really a pile of rubbish and no one should waste their time reading it,” he says.
Willett says it’s not helpful to look simply at how peoples body mass indexes, or BMIs, influence their risk of death — as this paper did without knowing something about people’s health or fitness. Some people are thin because they’re ill, so of course they’re at higher risk of dying. The study doesn’t tease this apart.
Also, he says the analysis doesn’t address the bigger, more important issues of quality of life. If an overweight person does live longer — is he or she living with chronic diseases?
If you’re hard-core, read the study yourself here, The New York Times report on it here or the boston.com report that explains more of the methodological issues here, and let us know what you think in the comments below.
My personal takeaway: The study’s lead author, Katherine M. Flegal of the CDC, strikes me as brave to take on accepted wisdom about ideal weight. But Walt Willett is a towering figure in nutrition research. So I think I’m going to use the ambiguities raised by this study and Flegal’s earlier work to reinforce the resolution I wanted to make anyway: This year, I’ll try to eat better but not make myself crazy about it.