A second study in the journal suggests that only severe obesity carries a high death risk - and that a few extra pounds might even provide a survival advantage. However, independent experts say the methods are too flawed to make those claims.
The study comes from a federal researcher who drew controversy in 2005 with a report that found thin and normal-weight people had a slightly higher risk of death than those who were overweight. Many experts criticized that work, saying the researcher - Katherine Flegal of the Centers for Disease Control and Prevention - painted a misleading picture by including smokers and people with health problems ranging from cancer to heart disease. Those people tend to weigh less and therefore make pudgy people look healthy by comparison.
Flegal's new analysis bolsters her original one, by assessing nearly 100 other studies covering almost 2.9 million people around the world. She again concludes that very obese people had the highest risk of death but that overweight people had a 6 percent lower mortality rate than thinner people. She also concludes that mildly obese people had a death risk similar to that of normal-weight people.
Critics again focused on her methods. This time, she included people too thin to fit what some consider normal weight, which could include people emaciated by cancer or other diseases, as well as smokers with higher risks of heart disease and cancer.
"Some portion of those thin people are actually sick, and sick people tend to die sooner," says Donald Berry, a biostatistician at the University of Texas MD Anderson Cancer Center in Houston.
The problems created by the study's inclusion of smokers and people with pre-existing illness "cannot be ignored," says Susan Gapstur, vice president of epidemiology for the American Cancer Society.
A third critic, Dr Walter Willett of the Harvard School of Public Health, iss blunter: "This is an even greater pile of rubbish" than the 2005 study, he says. Willett and others have done research since the 2005 study that found higher death risks from being overweight or obese.
Flegal defends her work. She says she used standard categories for weight classes. She says statistical adjustments were made for smokers, included to give a more real-world sample. She also says participants were not in hospitals or hospices, making it unlikely that large numbers of sick people skewed the results.
"We still have to learn about obesity, including how best to measure it," said CDC Director Dr Thomas Frieden. "However, it's clear that being obese is not healthy - it increases the risk of diabetes, heart disease and cancer. Small, sustainable increases in physical activity can lead to significant health improvements."
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