Children as young as seven believe they are too fat, and researchers warn they are at risk of developing eating disorders.

A study found almost half of girls and a third of boys aged between seven and 12 wanted to be thinner.

The research shows children are aware of their body shape and image at a much younger age than previously thought.

Children at seven are aware whether they are satisfied with their bodies

Dr Helen Truby, University of Surrey

It is believed they are influenced by images in the media of very thin celebrities such as Gerry Halliwell and Ally McBeal star Calista Flockhart.

Researchers from Surrey University and the Melbourne University, Australia studied 312 children.

Ideal image

A body mass index (BMI) measurement was taken - calculated by dividing weight in kilograms by the square of height in metres.

In adults, a BMI of more than 25 is classed as overweight, and over 30 as obese.

Click here to calculate your Body Mass Index

The children were photographed so that the researchers could identify the range of body sizes.

From these, the researchers generated a set of seven body images for both boys and girls.

The children were then asked to pick out which image they perceived to be most like their own, and which one they thought was an ideal figure.

The difference between perceived and ideal ratings was then used as a way of measuring dissatisfaction with body size.

Forty-eight percent of girls selected an ideal body image that was thinner than their own, 42% a figure the same size, and 10% a larger body size.

Among boys, 36% preferred a thinner body image, 44% the same, and 20% a larger image than their own.

Dissatisfaction

The research team, led by nutritionist Dr Helen Truby, from the School of Biomedical and Life Sciences at the University of Surrey say their findings support previous studies which indicated unhappiness with body size is frequent even before children reach puberty.

They say further research is needed to prevent such dissatisfaction developing into more serious body image and eating disorder problems in teenagers and adults.

And they call for the development of a specific BMI scale for children.

Dr Truby told a national newspaper: "It is surprising how many young children are aware of their body shape and size at such an early age.

"It was believed children didn't develop an adult ideal until puberty.

"But children at seven are aware whether they are satisfied with their bodies."

She added: "The consequences to public health in these findings in relation to the desire for a thin body, which is relatively unachievable for most children, needs careful consideration."

Physical activity

A spokesman for the Eating Disorders Association told BBC News Online: "This research illustrates the risks faced by developing youngsters as they begin to be influenced by adult aspirations and expectations."

Sarah Schenker, a dietician at the British Nutrition Foundation, told BBC News Online: "If children do diet, it should be done sensibly, with a healthy eating approach."

She added: "If children are overweight - and rates are increasing in this country - then obviously you would suggest that the child 'grows' into their weight.

"The way to do this is to try to encourage more physical activity, rather than looking at 'good' or 'bad' foods."

She warned children who tried "faddy diets" risked nutrient deficiencies which could affect their growth.

The research is published in the British Journal of Clinical Psychology.