Anorexia may be triggered by a defect in the brain, shows study.
The pioneering research, carried out on anorexics as young as eight and using powerful new brain-imaging techniques, could lead to different treatments.
Anorexia is defined as a body weight at least 15 per cent below that expected, the Daily Express reported.
"We believe subtle problems in early brain development make patients susceptible to anorexia. We need to re-examine other mental health problems," said Psychologist Dr Ian Frampton of Exeter University, one of two researchers leading the study.
The work was led by Professor Brian Lask of Great Ormond Street Children's Hospital, a leading expert on the potentially deadly eating disorder.
He and his team used novel scanning techniques to reveal that the brains of anorexics were malfunctioning in the insula, a key area that controls eating, anxiety and body image.
This persists after weight recovery, suggesting the problem exists before the onset of the illness.
Up to a third of sufferers are affected by the brain abnormality, which is highlighted only by the sophisticated tests. The team believes other biological causes in the brain affect the remaining two-thirds of sufferers, which is why so many patients relapse.
"They are predisposed to fail because the fault is there in their brains. You cannot easily cure people if there is an active defect," Dr Frampton explained.
The findings could help settle the debate that parents and size zero models cause anorexia due to unhealthy attitudes towards food and body image. It will also open up the debate about causes of other mental illnesses such as depression and bipolar disorder.
"The discovery of differences in the insula begins to explain why anorexics behave the way they do. Not all adolescents are susceptible to excessive dieting. It is only those who have this biological defect," Dr Frampton added.
He believes new therapies might help to control anorexia where up to 40 per cent of sufferers relapse within a year.
The study's results have been published in the journal Medical Hypothesis.