Researchers found that at 15 years of age, 26% of girls were on a diet compared to just 5% of boys.

Overweight girls of that age were three times as likely to be worried about their weight as overweight boys.

They were also much more likely to be on a diet, with one in two overweight girls watching what they ate, compared to just 16% of boys.

Most people who continually diet increase their risk of developing an eating disorder like anorexia nervosa

Eating Disorder Association spokesman

Girls are affected more rapidly and more profoundly by the physical changes of puberty, the researchers say, making it more difficult to convey messages about how to avoid excessive dieting and eating disorders.

Researchers from the University of Glasgow surveyed over 2,000 children at the ages of 11, 13 and 15.

Under exam conditions, they were asked whether they were worried about putting on weight and whether they were dieting to become slimmer at that time.

Researchers also calculated their body mass index, to see if the children were the right weight for their height.

Although there were significant differences between boys and girls worries about weight at age 11, the researchers found these had become "huge" by the time they had reached their mid-teens.

Puberty

Body mass index, as expected, increased with age.

It was only slightly higher in girls, who naturally tend to gain more fat in puberty than boys.

The proportion of children who were overweight went up from 16% at 11 to 17% by the age of 15.

But at each age, girls who were of medium to low weight were significantly more likely to be dieting than boys.

By 15, 26% of medium weight and 8% of low weight girls said they were dieting compared with under 3% of medium to low weight boys.

Media images

Similar patterns were seen when children were asked whether they were concerned about putting on weight.

Between the ages of 11 and 15, the number of boys worried about their weight fell.

But the number of girls who expressed concerns increased from 44% at 11, rising to 70% at 15.

Dr Helen Sweeting, a researcher at the Medical Research Council Social and Public Health Sciences Unit at the University of Glasgow, led the study.

She told BBC News Online: "We didn't ask the children why they were concerned about their body image.

"But we do see these differences in adults, and generally the answer is seen as media images."

The teens is an important time to ensure they are getting enough calcium

Dr Wendy Doyle

She added: "I would hope that the emphasis for children would be sensible eating, rather than dieting, combined with exercise."

A spokesman for the Eating Disorder Association said: "This definitely reinforces a tendency that we were already aware of.

"Most people who continually diet increase their risk of developing an eating disorder like anorexia nervosa."

Dr Wendy Doyle, spokeswoman for the British Dietetic Association, warned that by not eating properly, teenage girls could be storing up problems for the future.

She said it had previously been shown that a high proportion of girls in the 15 to 18 age range were not getting enough iron or calcium.

"We reach peak bone health in our mid-20s. After that we start losing it.

"The teens is an important time to ensure they are getting enough calcium.

"Iron is obviously important for young girls as they start menstruating."