Portland researchers have confirmed a popular 2005 study that found that slightly overweight people tend to live longer than normal-weight people, and far longer than the obese or overly skinny.
But before you grab the Haagen-Dazs, be warned: No one knows why this happens, and it doesn't necessarily mean bigger is better.
"These results do not imply that if you're in the normal weight range, you should go out and aggressively gain weight," which could cause new health problems, said David Feeny, an author of the new study who works at Portland's Kaiser Permanente Center for Health Research.
The original finding, from a study of U.S. residents, surprised and thrilled many folks. Roughly a third of U.S. adults are overweight, which doctors define as having a body mass index between 25 and 30. Another third of U.S. adults are obese, with BMIs above 30. A normal BMI is considered 18.5 to 25; people with BMI less than 18.5 are underweight.
The 2005 finding was matched earlier this year by Japanese scientists, whose work was hailed with headlines such as "Chubby People Live Longest."
Scientists with Kaiser, Portland State University and Oregon Health & Science University found similar results by tracking health surveys of 11,326 Canadian adults for 12 years. The overweight Canadians also lived longest, followed by the normal weight and mildly obese. The very thin and very obese (BMI above 35) were most likely to die sooner. The study, published online by the journal Obesity, also involved scientists with McGill University and Statistics Canada.
"The evidence is accumulating that overweight may be protective," Feeny said. "We need to understand why that might be the case and historically that wasn't."
One possibility is that screening and treatment have eased many problems associated with being overweight, such as high cholesterol and blood pressure. On the flip side, Feeny said, most people who die are elderly and lose weight as they age and get ill. So people carrying a little extra weight to start with may be more able to survive some health shocks as they age.
Scientists are still exploring the causes. Feeny said his group also will look at how weight affects quality of life and sickness, not just death. It's possible the findings will lead doctors to redraw boundaries of what weights are high, low and ideal.