Thursday, September 27, 2007
Bulimia as Food Addiction
Serotonin-mediated brain activity drives the binge-and-purge cycle
Bulimia, the binge-and-purge disorder that tends to afflict young women, seems especially linked to serotonin abnormalities. Bulimics gorge themselves and then induce vomiting--a debilitating cycle that often leads to severe health consequences.
Richard and Judith Wurtman, of the Massachusetts Institute of Technology (MIT) identified a subset of bulimics who binge severely and almost exclusively on high-carbohydrate foods. These bulimics tended to be mildly obese, severely depressed--and came from families with a strong history of alcohol abuse. Other researchers have reported that a significant number of bulimics are themselves abusers of alcohol and other drugs. What is being suggested is that carbohydrate-craving obesity and bulimia may turn out to be two additional forms of drug addiction. They may be variations on the addictive theme, and the underlying cause may be the same--irregularities in the reward system neurotransmitters.
For women whose bodies do not regulate the production of serotonin successfully, bulimia is one of the possible symptoms that can result from this condition. Unlike anorexia, its “partner” disorder, bulimia resembles addiction in several important ways. There is a definite “high,” which comes with the purging, and which has no analogue in anorexia. (Recall that serotonin is involved in smooth muscle functions, like vomiting and bowel movements.)
Bulimia’s impact on the brain’s reward center also seems to be quite direct, judging by the high relapse rates of bulimics. As further evidence, studies were performed by Walter Kaye and colleagues at the University of Pittsburgh Medical Center, where PET scans were taken of women who were former bulimics, and compared to a set of PET scans from healthy, age-matched women. The ex-bulimics showed a marked decrease in serotonin binding at the 5HT receptors, and studies by Kaye and others offer evidence that alterations in the brain’s serotonin pathways often persist after recovery from bulimia, and may represent permanent changes in brain chemistry.
The idea that serotonin disturbances are at the root of bulimia continues to make sense. Moreover, preliminary studies of female twins have bolstered the basic hypothesis, by showing evidence of a possible genetic predisposition toward bulimia.