10 April 2012 --- A third of Americans are now obese, and up to 70% of them are trying to lose weight. In a new study published in the American Journal of Preventive Medicine, researchers from Harvard Medical School and Beth Israel Deaconess Medical Center in Boston have found in a nationally representative sample that obese dieters who said they ate less fat, exercised more, and used prescription weight loss medications were more likely to lose weight. Diet foods and products, nonprescription diet pills, and popular diets were less successful, according to the researchers.

"Despite popular perception that obese people are unable to lose weight, a substantial number of obese participants in our study did report successful weight loss, suggesting that some obese U.S. adults can and do lose weight," says lead investigator Jacinda M. Nicklas, MD, MPH, MA, Clinical Research Fellow, Beth Israel Deaconess Medical Center and Harvard Medical School.

Investigators analyzed data from the 2001-2006 National Health and Nutritional Examination Survey, which collects demographic, health, and health behavior information from non-institutionalized U.S. adults. From the sample of over 4000 obese adults with a self-reported body mass index (BMI) of 30 or higher who participated in the in-home survey, they found that 63% of the respondents tried to lose weight in the last year.

Survey participants were more likely to report a weight loss of at least 5% of body weight if they reported eating less fat, exercising more, and using prescription weight loss medications. Those who lost at least 10% were also more likely to have joined a weight loss program. "Although national guidelines recommend a loss of 10% of body weight for improved health in the obese, studies have found that even a modest weight loss of 5% can lead to health benefits," says Dr. Nicklas.

Liquid diets, nonprescription diet pills, and popular diets showed no association with successful weight loss, and those who reported losing more than 10% body weight were less likely to report eating diet foods and products, compared to those who lost less. "Interestingly, although participants engaging in formal weight loss programs may be required to consume certain diet products or foods, in our study, adults who said they used diet products were actually associated with being less likely to achieve at least 10% weight loss," notes Dr. Nicklas. "This suggests that the structure of being in a program may be more important. It is possible that some dieters may be overeating diet products because they believe they are healthy, or low in calories."

In the study, prescription weight loss medications were associated with successful weight loss but were used by a small number of participants. "These results tell us that Americans use many weight loss strategies that are not associated with significant weight loss, including nonprescription weight loss medications. Public health efforts directing Americans to adopt more proven methods may be warranted," concludes Dr. Nicklas.