Boys are under almost as much pressure as girls to have the "perfect" body, a survey of teachers has suggested.
It also indicates that children as young as four are refusing to eat certain food for fear of being fat.
Pressure to live up to unrealistic body images is leaving many youngsters with anxiety issues, low self-esteem and in some cases is leading to children suffering from eating disorders, according to a poll by the Association of Teachers and Lecturers (ATL).
The survey, which questioned almost 700 teachers, found that 84% believe that there is pressure on girls to have or maintain a certain body image, with two thirds (66%) saying boys are facing the same issue.
And this pressure is increasing - almost two thirds (63%) of those surveyed said there is more pressure on young people to have a certain body image now than 10 years ago, while 51% said it has increased compared to five years ago.
There were also concerns that pupils who worry about their body image were trying to control their weight and appearance.
More than half (54%) of the teachers surveyed said that they knew of girls who had dieted due to concerns about their body image, with 30% saying they knew of boys who had started excessive exercise regimes. Some 22% said boys were using protein shakes and supplements to improve their physique. Almost half (48%) suggested that girls had developed eating disorders such as anorexia or bulimia due to pressure to live up to a certain body image.
ATL is due to debate two resolutions at its annual conference in Manchester next week calling for action on promoting health body images and the effect of pornography on pupils.
ATL general secretary Dr Mary Bousted said: "Young people are under tremendous pressure to have or maintain often unrealistic body images portrayed in the media. ATL members report that this not only impacts on female pupils but increasingly leads to low self-esteem, lack of confidence and anxiety in male pupils too.
"With academic and other social pressures young people already have enough to deal with. Comparing and competing not only with their peers on looks, but with airbrushed celebrities in the media only leads to misery. Of course, young people want to fit in and it's a hard part of growing up, but the pressure to have the 'perfect' body should not be at the detriment to children's well-being and happiness."