Sunday, June 12, 2005

My Favorite Obesity Study

Remember that CDC study not too long ago that the media interpretted as saying overweight people actually live longer? "Some Extra Heft May Be Helpful," the headlines said.

Well, on Popular Science's Soapbox, Rebecca Skloot targets the media's coverage of this study in her "Flabby Coverage." I learned a few things from her article, and so I want to quote a little bit of it here.

(emphasis added)
The deal is that the media didn't push to analyze the CDC report--they just jumped on good headlines. The study is titled "Excess Deaths Associated with Underweight, Overweight, and Obesity." How anyone could read that and reduce it to "Studies Show: Being Fat Is Not So Bad" is beyond me. These results corroborated an overwhelming body of research: Obesity is linked to deadly diseases. The CDC did find fewer people died in 2000 from obesity-related causes (111,909) than had been previously estimated (365,000). But estimating obesity deaths, as the sutdy points out, "raises complex methodologic issues," and its own methodology "has important limitations."

One of these is controlling for underlying disease. "Many diseases and medications cause people to gain or lose weight," notes Tobias Kurth, a Harvard University obesity researcher. "If you don't control for these and just look at who's dying and how big they are, you can get a skewed view of the world. Using this study to say being overweight is protective is simply overstating the scientific data." There's also the well-known "obesity paradox," that being slightly overweight can offer protection for the elderly, though the truly obese are less likely to grow old enough to see any such benefit.

The study's most obvious limitation is its use of the unreliable "body mass index" (BMI) . . . With a BMI of 27.1, [President George W. Bush is] "overweight." But President Bush is in great cardiovascular health . . .

Major-media coverage didn't raise these questions. Instead it tended to compound the problem with fuzzy math, often reporting that 25,814 Americans died from obesity, though the actual number was 111,909. Because the CDC study documented fewer deaths in the "overweight" category than in the "normal category, the media subtracted the number of overweight people who didn't die from the number of obese people who did--as if deaths that don't happen somehow cancel out deaths that do.

A companion study did find that overweight and obese people have lower cholesterol levels and blood pressure than they did in the past. It didn't show that obesity is inherently less dangerous; it showed that medicine has gotten better at treating some of its effects. Obese people may be living longer, but those extra years are full of heavy medication, diabetes, sleep apnea, stroke, asthma, blood clots, heart disease and cancer. And obesity is still one of the top causes of preventable death, which is why the CDC cautioned that people shouldn't use this study as an excuse to be overweight.

It's good news that people can live longer with obesity, but that's no excuse to blow off exercise and order more pie--precisely what the coverage has encouraged. And don't get me started on those huge fast-food-industry-funded ads declaring that obesity is offically "hype." They make me want to scream. There is no science saying that obesity is OK. That's not hype. It's scientific fact.

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