A national study has found the number of teenage girls with eating disorder behaviours has almost doubled to 18 per cent in the past six years.

It was six years ago when Dr Jenny O'Dea, Associate Professor in nutrition and health education from the University of Sydney, first embarked on a study of the eating habits of young Australians.

Dr O'Dea surveyed 5,000 children in schools across the country.

Last year, the number of children surveyed expanded to nearly 9,000. It revealed heartening news in some areas but disturbing figures in others.

For example, the number of teenage girls with eating disorder behaviours nearly doubled from one in 10 in 2000 to about 18 per cent in 2006.

"There was a doubling of the number of girls who said that they starved themselves for two days or more to try to lose weight," Dr O'Dea said.

"That was across the social classes. It wasn't high-income girls, it was low, middle and high-income girls.

"So we need to be careful - we don't want to promote this starvation, the vomiting, the laxative abuse, the cigarette smoking - that I found in this study."

Dr O'Dea says she was not surprised to see the figures rise, after studying the phenomenon for about 20 years.

"But I was really disappointed that it hadn't decreased, that it just keeps rising," she said.

"I was really disappointed because I know a number of schools and government agencies and various programs have tried to improve body image and eating disorders and this sort of fad dieting in girls, so I think there's room to improve there certainly."


Celebrity role models

But she says the programs against eating disorders are struggling against a society that sends a very different message.

"I think the crux of that sort of poor body image, that sort of desperate need to try to achieve the perfect body comes from this idea that, 'to be a better person, to have a successful life, to be happy, I have to lose weight - that's what western society tells me'.

"Celebrities have become very thin since the year 2000 - celebrities like Victoria Beckham, Paris Hilton, Nicole Kidman, they're very, very thin. They're probably underweight, clinically.

"I think girls look to these role models and say, 'I need to be like that to have a happy life'."

Dr O'Dea says teenage girls are also being influenced by media reports about obesity.

"I think what's happened is there's been a big media panic about child obesity - there's been a lot of talk about obesity, there's been a lot of hysteria," she said.

"There's been a moral panic about obesity and I think the teenage girls are picking up on that, girls from all different social class levels."


Obesity

But while eating disorder behaviour affects more teenage girls regardless of whether they are from a wealthy family or not, obesity is increasingly becoming more of a problem for the nation's poorer kids.

There have been Federal Government campaigns to tackle the problem of child obesity and Dr O'Dea says her study shows overall child obesity rates have steadied, with just a 1.3 per cent increase in six years.

But those figures do not reflect what is happening among children from lower-income families.

"The trend was there in 2000 for the lower-income children to be more likely to be obese or overweight and it's there again in 2006, and I think it's more pronounced in 2006," Dr O'Dea said.

"I think it's a trend that we really need to look at - how can we affect low-income schools, low-income families, disadvantaged families.

"The improvement in obesity has been almost exclusively in the high-income families and the high-income schools.

"I'm very careful to say that this is only a trend, it needs to be further analysed, but there is definitely a social class effect."