Bulimia is an eating disorder characterised by repeated episodes of compulsive and secretive eating of energy dense foods. These periods of gluttony are then followed by energy purges whereby vomiting, laxative abuse and fasting are undertaken. This period of purging is associated with depression and other negative mood changes, which can include feelings of self-loathing and desperation. These psychological changes contrasts significantly with the euphoria of the gluttony stage. The elevated mood states in the initial overeating periods of bulimia have lead some to conclude that bulimia is an addiction, with an underlying physiological basis originating in the reward pathways of the brain. In fact, animal studies looking at models of bulimia report that the overeating may relate to the release of opioids such as β-endorphin. Opioids may stimulate the reward pathways of the brain, producing drug like addictions and associated withdrawal. Therefore dysfunction in the reward system of the brain might explain the development of bulimia in humans.
The bulimia opioids link has been investigated by researchers. For example, in one study researchers1 measured the β-endorphin immunoreactivity in 34 female patients diagnosed with bulimia and compared them to 34 normal healthy patients who acted as controls. In the bulimic patient, the plasma β-endorphin immunoreactivity was significantly lower when compared to the control subjects. Further investigation using correlative statistic showed that the plasma levels of β-endorphin immunoreactivity were inversely associated with the severity of the symptoms within the bulimic group as measured by an eating aptitude test. The study authors were careful to remove the confounding variable of body weight within the analysis, by only including bulimic patients of normal weight. The bulimia opioids link was also independent of body weight or depressive symptoms. These results support a role for opioids in the aetiology of bulimia and invite speculation that bulimic behaviour might be an attempt by the patient to elevate β-endorphin levels
