Family influences seem to play a part, but again their exact role is not known. Both anorexia and bulimia tend to run in families, although the evidence for a genetic link is stronger with anorexia. Children also learn about eating behaviour and attitudes from their parents. There is great social pressure to be slim and attractive, although Dr Palmer believes the influence of fashion, advertising and the media is not enough on its own to explain why some women develop eating disorders but most do not. Athletes, models and dancers who need to keep their weight down are particularly prone.
Most sufferers have a low self-esteem and many find it difficult to express their emotions.
It is a myth, says Dr Palmer, that anorexia is a problem of the so-called upper and middle classes and that those with bulimia are ''striving, upwardly mobile types who live life in the fast lane''. People with eating disorders are often afraid to ask for help or feel they do not want to be helped. But the sooner the problem is recognised, the better the long-term prognosis, although recovery may take a long time. Only about half those diagnosed as having an eating disorder have recovered after five years. The Royal College of Psychiatrists estimates that at least 60,000 people are known to be suffering from anorexia and bulimia at any one time.