Fluoxetine decreases fat and protein intakes but not carbohydrate intake in male rats.

Administration of fluoxetine, a selective serotonin reuptake inhibitor, results in decreases in food intake and body weight. The present study investigated whether the anorectic actions of fluoxetine were due to a general decrease in caloric intake or macronutrient specific. Male Long-Evans rats were maintained on a dietary self-selection regime with separate sources of protein, fat, and carbohydrate. During the acute phase of the experiment, nutrient intakes were measured 2, 4, 6, and 24 h after injections of 0, 5.0, and 10.0 mg/kg fluoxetine hydrochloride. Fluoxetine significantly decreased protein and fat intakes in a dose-related manner at all measurement times. In comparison, fluoxetine had a less pronounced effect on carbohydrate intake. During the chronic phase, rats were divided into two groups, one receiving daily injections of 10.0 mg/kg fluoxetine, and the other, vehicle injections. Drug injections continued for 28 days, and were followed by a 28-day withdrawal period. Rats given fluoxetine on a chronic basis consumed significantly less calories and gained significantly less weight than rats injected with the vehicle. Both caloric intake and body weight returned to control values during the withdrawal period. Fat and protein intakes also were significantly reduced throughout the drug injection period, and were restored to baseline levels during the withdrawal period. In contrast, carbohydrate intake was not reduced on an absolute basis, and actually was increased as percent of total caloric intake during the drug period. The results of this experiment call into question the idea that increased serotoninergic activity is related to selective reductions in carbohydrate intake.