Children who regularly exercise and limit their time in front of the TV and computer are much less likely to be overweight than their peers, a new study suggests.

The American Academy of Pediatrics recommends that children devote no more than two hours per day to watching TV and playing video games.

Experts also encourage children to exercise regularly; some groups, including the AAP, recommend that boys move enough to take 13,000 steps each day, while girls should strive for 11,000. Another common recommendation is for children and teenagers to get at least one hour of moderate exercise on most, if not all, days of the week.

For the new study, researchers at Iowa State University in Ames looked at whether there were weight differences between children who met or did not meet recommendations for “screen time” and exercise.

They found that among 709 7- to 12-year-olds, those who did not meet either recommendation were three to four times more likely to be overweight than their peers who met both guidelines.

The findings are published in the Journal of Pediatrics.

Since the study compared groups of children at one point in time, it does not prove that following exercise and screen-time recommendations keeps children at a healthy weight, according to lead researcher Dr. Kelly R. Laurson.

However, the findings do show that screen time and exercise are each independently associated with the odds of a child being overweight, explained Laurson, who is now with Illinois State University in Normal.

This gives support to experts’ guidelines, the researcher told Reuters Health, and “parents should encourage their children to comply with both.”

Laurson and colleagues based their findings on 709 children from 10 schools in Iowa and Minnesota. They surveyed the children about their TV watching and video game habits, and they had each child wear a pedometer, or step counter, for at least four days in order to gauge his or her typical physical activity level.

Boys who took at least 13,000 steps per day were considered to be in line with exercise recommendations, as were girls who logged 11,000 or more steps.

The researchers found that among boys who met the recommendations on exercise and screen time, 10 percent were overweight. Among girls meeting both recommendations, 20 percent were overweight. That compared with 35 percent of boys and 40 percent of girls who met neither recommendation.

“Both physical activity and screen time are important factors in childhood overweight,” Laurson said.

Unfortunately, the investigators found, only a minority of children in their study were meeting experts’ recommendations. About 44 percent were getting enough exercise, while just 31 percent were limiting their screen time to less than two hours per day.

SOURCE: Journal of Pediatrics, August 2008.