And he adds that the pictures of extra-skinny celebs we see in magazines don't help, either.
Kate Winslett, star of Titanic, says she was called 'Blubber' at school.
She says it made her shy and she had problems with her weight for years.
The research shows that girls on diets tend to cut out meals, like breakfast and avoid certain foods.
Boys are more likely to turn to exercise rather than slimming.
Dr Hill hopes the study will help teachers to spot bullying and hopefully stop it.