Children as young as four are refusing to eat certain food for fear of being fat, a survey of teachers has found.
Pressure to live up to unrealistic body images leaves many youngsters with anxiety issues, low self-esteem and eating disorders, according to the poll by the Association of Teachers and Lecturers (ATL).
An early years teacher in England told researches: "I work with 4-5 year-olds and some say things like 'I can't eat cheese, it will make me fat'."
And a teacher at a primary school said: "I am very worried to hear little girls as young as 10 talking about being skinny and dieting."
The survey, which questioned almost 700 primary and secondary teachers in February and March, also indicated that boys are under almost as much pressure as girls to have the "perfect" body.
It found 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.
The school staff also expressed concerns that pupils who worry about their body image were trying to control their weight and appearance.
Young girls are using sunbeds or spray tans 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 just under a third (30%) saying they knew of boys who had started excessive exercise regimes.
In addition, over a fifth (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.
A head of department at a secondary school in England said: "I've heard girls aged 15 say, without a hint of irony, 'I'm dieting but I need to keep my boobs so boys will like me."'
Almost half (46%) also said that girls are wearing clothes to disguise their body shape, while over half (51%) suggested that girls are choosing outfits that "flaunt" their bodies, and 29% claimed that girls are using sunbeds or spray tans.
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."
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