While that number is larger than most weight-loss clinical trials report, the majority of Americans are still unable to lose weight and keep it off. Identifying those who lose weight and successfully maintain that loss may aid health professionals in developing approaches to help others maintain weight loss, the researchers say.
Two-thirds of the United States adult population is overweight, defined as a body mass index (BMI) of at least 25, or obese, a BMI of at least 30. Obesity rates, which doubled between 1980 and 2004, increase the risk of type 2 diabetes and high blood pressure. The recommendation is often to lose at least 5 to 10 percent of initial body weight with these conditions.
Weight loss and weight maintenance programs need significant changes in their effectiveness and availability to affect these numbers, note the researchers.
"It is important for health professionals to understand the true prevalence of long-term weight loss, as it may help to change the underlying beliefs and influence clinical practice," said Jennifer Kraschnewski, M.D., M.P.H., assistant professor of medicine and public health sciences. "Studies have shown that physicians may not believe offering weight loss advice and counseling is a worthwhile activity in clinical practice. An awareness of our findings may encourage health professionals to pursue weight loss counseling for overweight patients."
Previously, data came from either published clinical trials or the National Weight-Control Registry, comprised only of those able to lose at least 30 pounds and keep it off for a year. The registry does not represent the entire population, so it is not useful for providing estimates of long-term weight loss in the country.
Penn State College of Medicine researchers analyzed data from the National Health and Nutrition Examination Survey from 1999-2006, a nationwide survey evaluating the health and nutrition of a representative portion of the population. Participants of this survey self-reported weight status and history.
Researchers calculated BMI for each individual and determined if they achieved 5, 10, 15 or 20 percent long-term (long than one year) weight loss maintenance. The sample included 14,306 people: 52.3 percent men and 47.7 women. One-third stated a current goal of losing weight, with 82.6 percent classified as overweight or obese.
Thirty-six percent of the sample had maintained a weight loss of at least 5 percent of their initial body weight. This is a higher rate than clinical trials, which have shown only 10 to 20 percent of individuals able to maintain a loss of at least five percent. This difference may be that while those who participate in clinical trials are a selected population, the numbers in the current study include unintentional weight loss, or the current study captures temporary weight gain that is typically lost at specific instances, such as the so-called "freshman 15."
In the sample, women, adults age 75 to 84, non-Hispanic whites and those with less than a high school education showed stronger longer-term weight management.
"Identifying a significant percentage of the population that is succeeding in some weight loss may be an important target population for weight maintenance programs," Kraschnewski said. "Although the amounts lost are modest, if a substantial number of individuals achieved such losses, it would have a significant public health effect. Particularly, those individuals who have lost at least five percent and kept it off - one in three Americans who have ever been overweight - may represent a unique opportunity to reach a target population who has had some success but could benefit from greater weight loss efforts."
Other key findings of this study:
Researchers published their findings in the International Journal of Obesity.
Other members of the research team are Jarol Boan, M.D., M.P.H., associate professor of medicine, Christopher Sciamanna, M.D.,M.P.H, professor of medicine and public health sciences, and Jolene Esposito, research coordinator, Division of General Internal Medicine, Department of Medicine, all from Penn State College of Medicine; Nancy.E. Sherwood, Division of Epidemiology and Community Health, School of Public Health, University of Minnesota and HealthPartners Research Foundation; Erik Lehman, M.S., biostatistician, Department of Public Health Sciences, Penn State College of Medicine; Donna Kephart, M.H.A., senior instructor, Department of Public Health Sciences, Penn State College of Medicine.