The study, conducted by the American Cancer Society and published in the New England Journal of Medicine, tracked one million people, 300-thousand of whom were healthy non-smokers.
The researchers calculated each subject's body mass index (BMI), a ratio of weight to height, and tracked them for age and cause of death.
Among sample of participants the researchers found a gradually increasing risk for death beginning with a BMI of 25, which averages out to 150 pounds for a five-foot-five woman and 174 pounds for a five-foot-ten man.
The heaviest white men, with a BMI of 40 or more than 278 pounds on a 5-foot-10 frame, were 2.58 times more likely to die than their healthiest peers, men of the same height weighing 153 to 170 pounds. White women with a BMI of 40 or greater -- 240 pounds for a five-foot-five woman -- were twice as likely to die as their counterparts who weighed 132 to 148 pounds.
"We have not been successful in getting out the message that overweight in this country is a severe public health problem," says Eugenia Calle of the American Cancer Society. "The increase in risk really begins at the very early levels of moderate overweight and increases consistently and quite dramatically throughout the levels of severe overweight," she says.
Black women were the only exceptions to the rule. The study found the most overweight black women did not have a significantly higher risk for premature death than slender black women.
It makes for a fascinating scientific riddle, says June Stevens, a University of North Carolina nutritionist. "Although I had seen this in several other studies, I wasn't ready to believe it was true," she says. "Now I'm thinking maybe this is true, and we need to figure out why."
Still, Stevens and Harvard University Dr. JoAnn Manson say the study probably understates the risks of obesity for black women.
They point out that compared to their white counterparts, slender, non-smoking black women have a higher risk of death to begin with, probably because they have less access to health care and more undetected disease. That would make it appear that weight alone doesn't play a big role in death rates among black women. "It would be really unfortunate if we became more complacent about obesity in blacks than in whites," Manson says.
The study also found an especially clear association between excess weight and a higher risk of dying from heart disease or cancer. Unlike a similar study in 1998 that suggested being overweight is less of a problem as people grow older, this study found many more deaths among overweight people of all ages, especially those over 75.
More adults nd children are overweight than ever before, with 55 percent of American adults weighing more than they should.
Perhaps as a backlash to media images telling us thin is in, some recent studies have gone so far to suggest that it's OK to be overweight as long as you are healthy. This is a myth obesity experts want dispelled.
"I think that has been a vogue that we are trying to make people feel better about being overweight," says obesity specialist Dr. Louis J. Aronne. "I think it's high-time we started a comprehensive program to try to prevent obesityÂ…it's a lot easier to prevent than it is to treat."
This is a message we've heard before, but since more than half of all Americans are now overweight, it appears to be falling on deaf ears.