Researchers for the first time have found why eating is difficult for people suffering from anorexia nervosa.
People with anorexia nervosa - a disorder that tends to occur in young women- often say that eating makes them more anxious, and food refusal makes them feel better.
In order to provoke dopamine levels in the brain, which is released when people or animals eat tasty foods, Walter Kaye, professor of psychiatry and director of the Eating Disorder Treatment and Research Program at the University of California, San Diego School of Medicine, administered a one-time dose of the drug amphetamine.
In healthy women without an eating disorder, amphetamine-induced release of dopamine was related to feelings of extreme pleasure in a part of the brain known as a "reward" centre. However, in people who had anorexia nervosa, amphetamine made them feel anxious, and the part of the brain that was activated was, instead, a part of the brain that worries about consequences.
"This is the first study to demonstrate a biological reason why individuals with anorexia nervosa have a paradoxical response to food," said Kaye.
"It's possible that when people with anorexia nervosa eat, the related release of the neurotransmitter dopamine makes them anxious, rather than experiencing a normal feeling of reward. It is understandable why it is so difficult to get people with anorexia nervosa to eat and gain weight, because food generates intensely uncomfortable feelings of anxiety."
The study has been published in the journal International Journal of Eating Disorders.