The experiment began when scientists noticed that anorexia and bulimia tended to be passed down through family members. Eating disorders are not solely linked to societal and media messages. "Heritability is a much more powerful influence than culture. Although culture and society play some role, it's actually relatively minor compared to genetics," Walter Kaye, M.D., professor of psychiatry and director of the Eating Disorders Program at the University of California, San Diego, told Ivanhoe.
Researchers began their tests in the area of the brain called the insula, which regulates the way your body responds to internal changes like a lack of food or oxygen. Using MRI imaging, they tested the neurological reactions recovering anorexia patients had to the taste of sugar. In the healthy brain, the insula releases hormones for pleasure when presented with the taste of sugar, especially after a long period of hunger. However, the anorexic brain did not react as strongly to the taste of sugar, indicating a problem in the part of the brain that conveys rewords or emotions. "The kind of sensory pleasurable, motivational aspects of feeding just seem to be diminished in people with anorexia, which actually may explain why it's possible for them to lose so much weight," Dr. Kaye told Ivanhoe.
In addition, people with anorexia nervosa tend to not experience pleasure or live in the moment. They often have exaggerated and obsessive worries about the consequences of their behaviors, looking for rules when there are none and are overly concerned about making mistakes. Imaging studies suggest that individuals with anorexia have an imbalance between circuits in the brain that regulate reward and emotion and circuits that are associated with consequences and planning ahead. "They don't want to do things wrong. They want to do things right, and they don't like uncertainty. They're naturally very anxious, and it may be an over-activity of this part of the brain," said Dr. Kaye.
DEADLY DISORDER: While about 50 to 70 percent of affected individuals eventually recover, a significant proportion of patients develop a chronic illness or die, making anorexia the number one cause of death among psychiatric diseases. Symptoms of anorexia include the patient's refusal to maintain body weight at or above a minimally normal weight for age and height and an intense fear of gaining weight or becoming fat, even when the individual is underweight. Although anorexia is characterized as an eating disorder, it remains unknown whether there is primarily a disturbance of appetite or whether change in appetite is secondary to other issues such as anxiety or obsessional preoccupation with weight gain. Dr. Kaye and his team hope to use these new studies to develop treatments for people struggling with anorexia.
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Walter Kaye, MD
University of California, San Diego
San Diego, CA