DAVID GREENE, HOST:
OK, and let's turn to another study about weight. You might want to listen closely here. It suggests that being a little overweight may tip the odds in favor of living a longer life. That's right - researchers say there may be some benefit to having a little extra body fat.
But not so fast. As NPR's Allison Aubrey reports, no one is suggesting you ditch the exercising, or end the diet.
ALLISON AUBREY, BYLINE: This isn't the first time that researchers have raised questions about the link between body weight and how long someone will live. While there's no debate that being severely obese will raise the risk of all kinds of illnesses and even cut some lives short, it's less clear what happens to people who are less overweight.
When Katherine Flegal, of the CDC, set out to answer this question, she wanted to include as many people as possible in her study; from as many places around the world as she could find.
KATHERINE FLEGAL: We searched all the literature - thousands of articles; found almost 100 articles with almost 3 million people that really addressed this question head on.
AUBREY: And she concludes that being overweight is actually associated with a lower risk of death. It's certainly not dramatic, but about a 6 percent decreased risk.
FLEGAL: Statistically significant.
AUBREY: So who are we talking about here? A lot more people than you might think. About one-third of all Americans fall into this category of overweight. And Flegal found that even among those who are technically slightly obese, there was no increased risk of death.
Now, at a time when we are bombarded with weight- loss messages, Flegal says it's not popular to suggest that heavier people may live longer. In fact, a few years back, when she published a paper that came to a similar conclusion, her findings were attacked.
FLEGAL: Our articles got called rubbish and ludicrous, that though - you know, it's really opened you up to a lot of criticism. I discovered - much to my sorrow - that this is a kind of a flashpoint for people.
AUBREY: One of the experts who takes issue with Flegal's conclusions is Walter Willett, of the Harvard School of Public Health. He's read her new paper, and he says he's not buying it.
WALTER WILLETT: This study is really a pile of rubbish, and no one should waste their time reading it.
AUBREY: Willet says it's not helpful to look simply at how people's BMIs - or body mass index - 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. This study doesn't tease this apart. Also, he says, the analysis does not 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?
WILLETT: We have a huge amount of other literature showing that people who gain weight or are overweight, have increased risk of diabetes, heart disease, stroke, many cancers, and many other conditions.
AUBREY: Willett says for listeners out there who want to know whether their body weight is a problem, one thing to do - rather than comparing your BMI to those around you - is to think about what you weighed when you were 20 years old.
WILLETT: For most people, our ideal weight - if we weren't seriously overweight at age 20 - is about what we weighed then. And that's why weight change is a good number to keep an eye on because it can be an early warning sign.
AUBREY: That you're on the path to more weight gain. Now, not everyone's convinced that the new paper is rubbish. Dr. Steven Heymsfield, of the Pennington Biomedical Research Center in Baton Rouge, says there are a couple of scenarios in which extra body weight might help people live longer.
DR. STEVEN HEYMSFIELD: If you fall, and you fall on a vulnerable bone - like the hip - that having a little extra fat there might protect you from a hip fracture.
AUBREY: Or, he says, if an illness leaves you unable to eat, extra body fat could be useful. Heymsfield acknowledges this is just speculation. He says while this paper won't end the debate over whether a little extra body fat could be a good thing, he says it does show that the relationship between weight and health may be more complicated than just a simple calculation.
Allison Aubrey, NPR News.