Children who are taught at school how to watch television "intelligently" lose weight within six months and reduce the levels of fat in their bodies, scientists have shown.

Children who are taught at school how to watch television "intelligently" lose weight within six months and reduce the levels of fat in their bodies, scientists have shown.

New research, published in a special edition of The Journal of the American Medical Association focusing on obesity, shows that children who were given lessons on how to watch television reduced their viewing time voluntarily by four hours a week and ate fewer meals in front of it. Within six months their body mass index - weight in kilograms divided by height in metres squared - was lower than their peers and their triceps skin thickness, which indicates fat levels, was substantially reduced.

Most attempts to reduce childhood obesity that involve reducing fat and energy intake and increasing physical activity have failed to reduce children's body fatness, the researchers said. However, teaching children to watch television "intelligently" has been shown to be effective.

In Britain, parents and doctors have been alarmed at the numbers of children who are getting fatter. There has been widespread speculation that obesity levels among the young are increasing because of greater viewing of television and videos. Children spend more time watching television or playing computer games than anything except sleeping.

A recent report showed that in Britain, 15.8 per cent of two-year-olds were overweight with 6 per cent categorised as obese. By their fifth birthday, 18.7 per cent were overweight, with 7.2 per cent categorised obese.

Gaynor Bussell, of the British Dietetic Association, said teaching children at school how to watch television would be very beneficial in countering childhood obesity. "It could be incorporated into the curriculum along with healthy eating and healthy lifestyles," she said. "It's a good lesson to learn at school. Families also need to be involved and do deals with their children, where they are allowed to watch a certain amount of television if they also walk to the shops or do some gardening."

The research conducted by scientists at Stanford University School of Medicine, in California, involved 200 eight-year-old children. Half of the children received 18 lessons on how to watch television, and the others acted as a control. The children and their parents were interviewed separately on how much television they watched and how much time they spent on the computer. Their weight, height, waist, and fat levels were measured initially and then after six months.

Children who attended the classes were less likely to eat snacks or meals in front of the television. They also watched fewer videos and played fewer video games at the end of the six months. They ate on average two meals a week in front of the television compared with 3.5 meals for the children who did not attend the classes.

"This intervention, targeting only television, videotape and computer game usage, produced statistically significant and clinically relevant changes in body weight, fat levels and size," said Dr Thomas Robinson, the report's author. "Even a small downward shift in the fat levels in the population would be expected to have large effects on obesity-related morbidity and mortality."