The eating disorder anorexia nervosa could be caused by a brain dysfunction, rather than social pressures, according to a radical new theory.
Researchers at St George's hospital in Tooting, south London have found that sufferers from anorexia have an abnormality in the blood flow to an area of the brain which affects body image.
In results presented for the first time yesterday at an international conference in London, they say this points to a biological cause for the condition.
More than a million people in Britain alone suffer from eating disorders which have been thought to be caused by social and cultural pressures to be slim.
There are 11 new cases of anorexia diagnosed annually per 100,000 population, 90 per cent of them women, according to the Eating Disorders Association.
Bryan Lask, professor of child and adolescent psychiatry at St George's Hospital and an expert on anorexia who led the latest research, said the finding of a biological cause could change the way it was treated.
"The biological cause has been under-emphasised and the socio-cultural pressures have been over-emphasised. There has to be a biological contribution otherwise everyone would be anorexic given the socio-cultural pressures in our society," he said.
"I am not saying people are born anorexic any more than they are born asthmatic or diabetic. But I am saying some people are born with a genetic pre-disposition to anorexia which makes it more likely to develop.
"If you live in a society which promotes thinness as the ideal then you are more likely to develop anorexia if you have the biological predisposition."
The study of 60 patients, some of whom have been followed for a number of years, is to be published in the International Journal of Eating Disorders.
The researchers used brain imaging and neurological testing which revealed the abnormal blood flow.
"There is a low blood flow in one specific part of the brain on one side. It only occurs in people with anorexia and does not occur in people without anorexia," Professor Lask said.
The part affected, called the insula, links other key parts of the brain involved in the disorder.
Anorexia is marked by intense feelings of anxiety, linked with the amygdala, restlessness and irritation (basal ganglia), obsessive thoughts (frontal lobe), visuo-spatial difficulties (parietal lobe) as well as body image (the somato-sensory cortex).
"You can think of these parts of the brain like London train stations, linked by the Circle line. If there is an obstruction on the Circle line, none of the stations will work properly and that is what we think is happening," added Professor Lask.
"The reduction in blood flow is in the insula but it causes abnormalities in different stations of the brain linked with anorexia," he said.
Anorexia is defined as a body weight maintained at least 15 per cent below that expected for the individual's height and age and has the highest death rate of any psychiatric condition.
Professor Lask said the abnormal blood flow observed in the brain imaging studies was more likely to be a cause than an effect of weight loss.
"It is such a specific effect in only one part of the brain. If it were the result of starving yourself you would expect global changes round the brain. And it tends not to return to normal when weight is regained. That is why we think it is cause rather than effect."
The discovery could ultimately point the way to a new treatment for anorexia to "tackle the basic fault," he said. But that could be ten to 20 years away.
"This has helped us explain the difficulty people with anorexia have in inhibiting tormenting thoughts. They become totally obsessed with the idea that they are fat and overweight. It will enable us to put our energy into trying the alter their thinking processes."