Eating disorders being a fairly common psychiatric diagnosis and having one of the highest mortality rates of all psychiatric disorders, research into the causes and possible therapies is pressing. Serotonin seems to play a role in anorexia nervosa (AN), specifically in mood dysregulations. Patients with AN tend to be anxious, obsessive, perfectionist and harm avoidant, all traits which are as well premorbid as symptomatic and often exist even after recovery. It has been suggested that increased activity of brain serotonin systems could contribute to this pathologic condition. Dieting in AN, which serves to decrease plasma tryptophan levels, may help to reduce symptoms of dysphoric mood.
Kaye et al (2003, International Journal of Eating Disorders) investigated the effect of ATD on currently symptomatic AN patients, recovered AN patients and healthy controls. Mood was self-assessed at baseline and hourly after ATD. Interestingly ill and recovered AN patients had significantly higher mean baseline TRP/LNAA (tryptophan/large neutral amino acids) ratios compared with controls. ATD caused a significant reduction in the TRP/LNAA ratio for ill (-95%) and recovered AN patients (-84%) compared with controls (-70 %). Both ill and recovered AN patients had a significant reduction in anxiety under ATD compared to a balanced control mixture. These data demonstrate that a reduction of tryptophan seems to be tied to decreased anxiety in people with AN. Restricting dietary intake of tryptophan could present a way for individuals with AN to modulate dysphoric symptoms.
In contrast to anorexia nervosa, data suggest that serotonin activity is reduced in women at normal weight who have bulimia nervosa. Weltzin et al (1995, American Journal of Psychiatry) tested whether ATD could alter short-term eating behavior and mood in women with and without bulimia nervosa. Women with bulimia nervosa exhibited an increase in caloric intake and mood irritability after acute tryptophan depletion, which contrasts findings by Kaye et al in AN patients. These results indicate that women with bulimia nervosa have an exaggerated or pathological response to a decreased serotonergic neurotransmission.