MORE than a third of teenage girls in the UK risk harming their development by dieting, according to a survey published today.

A national study shows 37% of girls aged 13-18 admit to eating less than 1200 calories a day in a bid to slim, 40% less than they need.

And while fewer boys diet, almost a quarter admit to limiting themselves to fewer than 800 calories.

According to the survey carried out for supermarket giant Sainsbury's, almost every Scottish teenager questioned thought they knew what was meant by a healthy diet and more than three quarters reckoned they ate healthily.

But further questioning showed a shocking level of ignorance with more than half of them eating less than half the recommended "five a day" portions of fruit and veg.

Charlotte Park, a nutritionist with the grocery firm said: "The results show teenagers struggle to understand what constitutes a balanced diet.

"It is clear we need to help teenagers and their families to achieve a healthy, balanced lifestyle."

Sainsbury's has arranged a summit between teenagers, government figures and its chief executive Justin King to tackle issues including junk food, diet and exercise.

Mr King said: "We want teenagers to help us develop practical suggestions and new ideas for young people and their families to make informed choices about their health and the food they eat."