Restricting the amount of time young children spend watching TV and playing computer games can help them shed calories from their diets and lower their risk of becoming obese, U.S. researchers said on Monday.

The study involved children aged 4 to 7 years whose body mass index (BMI) was at the 75th percentile or higher for their age and gender. On average, all of the children regularly watched TV or played computer games at least 14 hours per week at home.

Researchers attached a $100 electronic device called the TV Allowance, made by Mindmaster Inc, to televisions and computers in the homes of half of the 70 volunteer families. The device controls the amount of screen time users have and was programmed to cut the usual time children used the device by 10 percent. When their allowance of screen time was used up, the TV or computer would not work.

By the end of the study, the children with the special monitor in their homes cut their use by about 17.5 hours a week, compared with a decrease of about 5.2 hours a week in the other group. Over two years of observation, the BMI fell in the group with the monitor.

It looks like screen time is influencing eating more than physical activity, said Leonard Epstein, a professor of pediatrics at the State University of New York at Buffalo.

It's possible that when there is a regular pairing of eating and watching TV, just watching television becomes a cue for eating, he said. And television can also be a distraction from how much you are eating.

In the study, 30 percent of the children in the TV Allowance group who started out the experiment overweight grew out of the excess pounds and weren't too heavy after two years, Epstein said. In contrast, only 18 percent who were allowed an unrestricted amount of television and computer time were no longer overweight at the end of the trial.

Randal Levenson, the president of Mindmaster and inventor of the TV Allowance, said he created the device in 1991 in a bit to control the amount of time his own children spent in front of the television. He found that it worked and now thousands of the devices are sold each year across the country.

Grades go up and kids get fitter if you reduce TV time,'' he said. I'm not anti-television, I'm anti-too much TV.''