More than 90 percent of men and 70 percent of women participating in a 30-year population study became overweight or obese--even if they were of normal weight at the start of the study. Results from the study of more than 4,100 U.S. adults suggest the risk of becoming overweight or obese are extremely high--both in the short and long term. Overweight is currently defined as having a body mass index (BMI) of 25 to 29.9, with obesity marked by a BMI over 30.

Almost 20 percent of female participants and 30 percent of men became overweight within four years of the study start in 1971; an additional 7 percent of women and 9 percent of men become obese. By study's end, more than half of all participants were overweight, with an additional one-third of women and one-quarter of men classified as obese.

Because only white men and women were included in the study, the researchers were unable to ascertain whether the results would apply to other ethnic groups. In addition, younger participants (those under 50 at study start) became overweight or obese at earlier ages than the older participants. The researchers noted, therefore, that the rate of becoming obese or overweight determined in this study may not apply to adults already in middle-age--possibly because they're already there.

"National surveys and other studies have told us that the United States has a major weight problem, but this study suggests that we could have an even more serious degree of overweight and obesity over the next few decades," says Elizabeth G. Nabel, M.D., director of the National Heart, Lung and Blood Institute, part of the National Institutes of Health (NIH) and the sponsor of the study. "We hope these results will serve as a wake-up call to Americans of all ages. Even those who are now at a healthy weight need to be careful about maintaining energy balance to avoid gaining weight. Taking simple steps to make sure that the overall the number of calories you consume do not exceed the amount you burn can play a major role in lowering your risk for many chronic conditions." Excess weight increases the risk of developing a host of degenerative diseases, including diabetes, hypertension, heart disease, stroke and arthritis.

The study appeared in the Oct. 4 issue of the Annals of Internal Medicine (143:473-80, 2005).