Heavy children who lost weight kept the pounds off better through weight maintenance follow-up, but even that wasn't terribly successful over two years, researchers reported.

The less-than-perfect results underscore the challenge in fighting the nation's obesity epidemic. About 34 percent of American children are overweight.

A team led by researchers at Washington University School of Medicine in St. Louis found that obese children who lost weight kept it off if they were in a maintenance program, but its effectiveness waned over time.

The research involving 150 overweight 7- to 12-year-olds is one of the first large-scale studies to evaluate the long-term effects of weight-loss maintenance strategies in children.

The study, which appeared in Wednesday's Journal of the American Medical Association, also is the first to look at whether heavy kids benefited from being encouraged to play with more physically active peers, cope with teasing, and develop an improved body image.

"We know from the adult field that the biggest challenge is not losing weight — it's keeping it off in the long term," said lead author Denise Wilfley, who heads the weight management program at Washington University.

Kids face the same struggle, she said.

The researchers studied obese youngsters from 1999-2004 at a university clinic in San Diego, where Wilfley used to teach. The children weighed at least 65 percent more than their recommended weight. All of the children in the study also had at least one parent who was overweight.

Each child and parent went through a five-month weight-loss program that set goals and emphasized healthy eating and exercise. They were also counseled by behavioral therapists.

On average, after five months, the children lost about 11 percent of their weight. They were then randomly assigned to one of three groups for four months.

One group was given no further instruction. Another group focused on self-monitoring and vigilance and used other behavior skills, trying to lose weight right away if they regained it.

In the third group, the youngsters were guided into play dates that involved physical activity and healthy eating; they were encouraged to make friends with more physically active peers. They also were counseled on body image and how to cope with teasing.

Researchers checked progress after one year and again after two years.

Those in the behavior skills and social groups were better able to keep weight off in the short term than those who had no intervention. However, the effects waned somewhat during follow-up. The kids left to their own devices regained their lost pounds, and then some, after two years.

The best outcome was for socially adept children who were encouraged to change their playmate networks. Most of those children were able to maintain nearly the same weight they had after the weight-loss program.

More work needs to be done to combine the best of the approaches, Wilfley said, perhaps extending the time spent teaching skills to maintain weight.

The alarming number of obese kids means researchers have to develop better ways of helping them lose and keep the pounds off, Wilfley said.

She plans to pursue the idea that spending time with healthy and physically active peers can help kids control their weight over the long haul.

Dr. David Ludwig of Children's Hospital in Boston praised the study's family-based effort. However, he said it wasn't large enough to "make a confident, definitive statement about which approach is better" at maintaining weight loss.

Terry Huang, childhood obesity director at the National Institutes of Health, which funded the study, said the social group's better results are exciting.

"It's not enough to focus on behavior modification," he said. "We have to start looking at obesity in the social context."

For two San Diego teens, the strategies were helpful.

As a chubby second-grader, "I used to look at myself in the mirror, and think, 'Oh, I'm so fat,'" said Katie Roetker, now 15. "Most days (now) I look in the mirror and think, 'looking good.'"

Katie, who took part in the new study, eats more fruits, vegetables and grains. She has given up fast food, and walks and takes dance classes.

Claire Carlson, 17, was nearly 30 pounds overweight when she was part of a pilot for the study in 1999.

Now, she says, "Eating healthy and exercising is second nature to me."

She's on the school swim team and surfs almost daily.