Many heavy teens lose weight for their own sake rather than to impress their peers or please their parents, according to a recent study.

Researchers from Brigham Young University found that more than 60 percent of teens described their health as the primary motive. About 43 percent identified peer acceptance as a factor.

"Most parents have the view that their teen is largely influenced by other people's perceptions of them," researcher Chad Jensen said in a statement. "Our findings suggest that teens have motivations that are more intrinsic. One implication is that parents should help to focus their teen on healthy behaviors for the sake of being healthy more than for social acceptance."

For the study, researchers looked in-depth at the success stories of 40 formerly obese or overweight teens. On average the participants shed 30 pounds, moving them from the obese to the normal weight category. They also maintained their healthier weight for a full year.

In the interviews, nearly all of the teens emphasized that it was their own decision to lose weight. According to teens, parents provided the most help simply by modeling healthy behaviors and providing healthier options for meals and snacks.

And timing really helps, Jensen said.

"There were some periods, like a transition to high school or to college, where we saw groups of teens who lost weight in those important periods," Jensen said. "It's sort of an opportunity to re-make yourself. There's a lot of change going on, so some teens decide to make a change to be healthier."

Another recent study found that 30 percent of adolescents in the United States are overweight or obese. Jensen said that the popularity of The Biggest Loser helps increase awareness of healthy lifestyles, but he fears that it sets unrealistic expectations because of the seemingly instant results.

"None of these teens in our study lost weight in a hurry," Jensen said. "Their advice to other teens is to stay the course and sustain it over the long term. For most of them it was just a pound or two a week."

The findings are detailed in the journal Childhood Obesity.