The reason behind anorexia could be the sex hormones in the womb, says a new study.
Researchers contemplate that some mothers might overproduce oestrogen, which affects the baby's brain, making it susceptible to the eating disorder.
The findings were based on a study, conducted by Marco Procopio, a psychiatrist from the University of Sussex and team, which reviewed the records of thousands of Swedish twins, held in a database.
The researchers found that the risk of developing anorexia was higher in girl twins than in boy twins.
It is generally claimed that girls who become anorexic are influenced by images of stick-thin models.
The findings of the latest study do not disprove this, but suggest that biology as well as culture plays an important part.
"We know that women are ten times more likely to develop anorexia than men and this study goes a long way to explaining why. We know that oestrogen and other hormones can have a powerful effect on the body and it would seem that there is an 'over expression' of oestrogen by the mother and the girl twin in some pregnancies," TimesOnline quoted Procopio, as saying.
"Oestrogen would be present in the amniotic fluid that bathes babies in the womb and would be swallowed by both the male and female twin. Oestrogen is needed in development of females but it is possible that too much affects the structure of the brain.
"Research into twins is a way to examine the factors involved, as the single most important period for brain development is during the months of pregnancy.
"The one thing we are certain of is that there is a genetic disposition to anorexia. Some scientists have suggested that upbringing may be a factor in the gender difference in rates of occurrence of the disorder, but studies haven't borne this out," he added.
Procopio said that he does not believe that thin models are responsible for the condition.
"If that were the case, we would have many more anorexics," he said. "There might be an effect on some girls but I doubt if these are truly anorexic but more likely a passing phase," he said.
Dee Dawson, who runs the pioneering North London Rhodes Farm clinic for teenage anorexics said: "I think that there is a genetic predisposition and the problem may well be to do with the formation of the brain in pregnancy. But often the triggers are problems at home so if you are susceptible in your brain make-up it could be triggered off by events in a teenager's life."