Oxytocin reduces caloric intake in men

OBJECTIVE Preclinical studies indicate that oxytocin is anorexigenic and has beneficial metabolic effects. Oxytocin effects on nutrition and metabolism in humans are not well defined. It was hypothesized that oxytocin would reduce caloric intake and appetite and alter levels of appetite-regulating hormones. Metabolic effects of oxytocin were also explored. METHODS A randomized, placebo-controlled crossover study of single-dose intranasal oxytocin (24 IU) in 25 fasting healthy men was performed. After oxytocin/placebo, subjects selected breakfast from a menu and were given double portions. Caloric content of food consumed was measured. Visual analog scales were used to assess appetite, and blood was drawn for appetite-regulating hormones, insulin, and glucose before and after oxytocin/placebo. Indirect calorimetry assessed resting energy expenditure (REE) and substrate utilization. RESULTS Oxytocin reduced caloric intake with a preferential effect on fat intake and increased levels of the anorexigenic hormone cholecystokinin without affecting appetite or other appetite-regulating hormones. There was no effect of oxytocin on REE. Oxytocin resulted in a shift from carbohydrate to fat utilization and improved insulin sensitivity. CONCLUSIONS Intranasal oxytocin reduces caloric intake and has beneficial metabolic effects in men without concerning side effects. The efficacy and safety of sustained oxytocin administration in the treatment of obesity warrants investigation.