The findings, published in the British Medical Journal, suggest that exercise is the safest way for teenagers to control their weight. This is confirmed by a second study, published yesterday in the United States journal Archives of Paediatrics, showing that television is linked with the growth of obesity among American teen- agers.
The US study of 1,300 students showed that a school-based program which aimed to cut down television viewing to less than two hours a day increased activity among the students and reduced their exposure to commercials for sweets and junk food. Over two years, obesity fell among the girls who went to schools involved in the programme (from 23.6 per cent to 20.3 per cent) and rose among those at control schools where it did not run (from 21.5 to 23.7 per cent). Among boys there was little change.
The BMJ study, conducted in Australia, found that 8 per cent of the girls had followed strict diets and a further 60 per cent had dieted at a moderate level. Over one year the strict dieters had an almost one in five chance of developing an eating disorder, while the moderate dieters had a one in forty chance. Boys were at much lower risk.
Psychiatric problems were also found to be strongly associated with the development of eating disorders, raising the risk almost sevenfold.
Professor George Patton and his colleagues, from the University of Melbourne, say that it is possible that the link between strict dieting and eating disorders exists because in those who start severe dieting a process leading to the development of an eating disorder has already begun. However, they conclude: "In adolescent weight control, promotion of exercise rather than restriction of dietary intake may prove less of a risk in the development of eating disorders."
The authors say previous research had suggested that taking part in sports, especially those that required thinness such as gymnastics, might increase the risk of eating disorders. However, they found that daily participation in sports did not raise the risks above those already associated with dieting.