Common to repetitive episodes of weight gain or failures to succeed on weight loss regimens is the excessive consumption of carbohydrate-rich foods in association with dysphoria. The brain neurotransmitter, serotonin, seems to be involved in the abnormal regulation of mood and food intake that underlies diet failures or weight gain in individuals who suffer from carbohydrate craving obesity (CCO), premenstrual syndrome (PMS) and seasonal affective disorder (SAD). All 3 syndromes are characterized by episodic bouts of increased carbohydrate consumption and depressed mood. Studies with dietary treatment or drugs that enhance serotoninergic neurotransmission have found that increased serotonin neurotransmission is associated with normalised food intake and mood. These results suggest that periodic intervention with dietary or drug treatment that increases serotonin availability may help sustain weight or assist in weight loss.