You may have more success losing weight if you try and do it with someone else, new research shows.

"Group-based weight-loss treatment produced weight loss, whether delivered by a professional or peer counselor," said study author Angela Marinilli Pinto, assistant professor of psychology at Baruch College of the City University of New York. "When people are in a group with others on the same journey, they feel there is that element of, 'OK, this worked for him or her, perhaps it will work for me. Perhaps I can give it a try.'"

The research was published Oct. 9 in the journal Obesity.

Pinto and her team randomly assigned 141 overweight or obese men and women to one of three groups.

One group got 48 weeks of behavioral weight-loss treatment from a health professional.

A second group participated for 48 weeks in Weight Watchers, where the meetings are led by members who have achieved and maintained a healthy goal weight.

A third group got combined treatment. They first had 12 weeks of behavioral weight-loss treatment from a health professional, and then transitioned to 36 weeks of Weight Watchers participation.

Pinto said she chose Weight Watchers because it is the largest commercial program in the United States. It is also oriented to behavior change and included information on modifying the diet and increasing physical activity to lose weight and maintain the loss.

Pinto's team was testing the hypothesis that the combination approach would produce a bigger weight loss than going to Weight Watchers alone. Starting with the professionally trained leaders, she thought, would be a good jump start to the weight-loss program.

The findings were a surprise. At 48 weeks, the researchers found no evidence that adding brief treatment led by professionals, and then transitioning to the Weight Watchers program, improved results.

At 48 weeks, those in the professionally led group lost 11.9 pounds, while those only in Weight Watchers lost more (13.2 pounds). The combination group lost the least -- 7.9 pounds, on average.

"The losses in the Weight Watchers group were greater than the losses in the combined group," she said. "The weight loss in the professionally led group didn't differ statistically from either [of the other two] groups."

"The Weight Watchers group produced better weight loss than this novel approach [of combining peer and professional]," she said. "Better meeting attendance is associated with better weight losses."

Those in the Weight Watchers group were more likely to lose 10 percent or more of their starting weight than the other groups. Losing 10 percent of excess weight is viewed by experts as enough to make a difference in disease risk.

Although more than one-third of those in the Weight Watchers group lost 10 percent or more of their starting weight, 15 percent of those in the combined group did and 11 percent of those in the professionally led group did.

The study shows that there is no evidence that adding professional guidance improves weight loss over peer-led groups.

Nearly 70 percent of American adults are overweight or obese, Pinto said. The study results may provide a practical solution for them.

The research was funded by the U.S. National Institutes of Health. Weight Watchers gave the participants vouchers to enroll, but had no say in the research. Pinto said she has no ties to Weight Watchers.

The results are a bit surprising, said Connie Diekman, director of university nutrition at Washington University in St. Louis, because most evidence has found that education by registered dietitians or behavior therapists enhances understanding of weight loss and boosts adherence.

"The study does demonstrate that regular involvement in weight-loss classes helps with weight loss," she said. "This point should be considered when people think about weight loss -- doing it alone may not yield success."

Professionally led programs vary in price, with Weight Watchers costing $10 per week and others priced at $35 a week or more, Pinto said.