The inability to control food intake and to engage in consistent exercise may account for repetitive episodes of weight gain. Many individuals who fail to maintain a normal weight may be susceptible to daily, monthly or seasonal perturbations in mood which result in an excessive intake of carbohydrate-rich foods and resistance to engaging in physical activity. Brain serotonin appears to be involved in these disturbances of mood and appetite; recent studies have shown that dietary and pharmacological interventions which increase serotoninergic activity normalize food intake and diminish depressed mood. Preventing recurrent weight gain may require periodic or sustained interventions that maintain mood and control over food intake.