Bingeing behavior and plasma amino acids: a possible involvement of brain serotonin in bulimia nervosa

It has been suggested that bingeing and vomiting behavior may be an attempt to suppress hunger or reduce dysphoria. Theoretically, such relationships could involve a mechanism whereby bingeing and vomiting change plasma amino acids which, in turn, enhance brain serotonin-mediated satiety and/or improvement in mood. This hypothesis is based on data showing that the intake of dietary carbohydrates increases the uptake of tryptophan (TRP), the precursor of serotonin, into the brain by increasing the plasma TRP ratio (the ratio of the plasma TRP concentration to the summed concentrations of other amino acids that compete with TRP for brain uptake). Plasma prolactin (PRL) release might reflect the activation of this system. We found that an increase in the TRP ratio during bingeing and vomiting was associated with satiety (i.e., cessation of bingeing and vomiting), but not change in mood. In other words, bulimic subjects who developed an increased plasma TRP ratio during bingeing and vomiting had fewer cycles of bingeing and vomiting and a greater increase in plasma PRL than did subjects who did not develop an increase in the plasma TRP ratio. This study raises the possibility that an increase in the TRP ratio may be associated with the termination of bingeing and vomiting, perhaps due to its effects on brain serotonin metabolism.