Exciting advances have led to the concept that hormones can modulate appetite and food intake. Oxytocin is a peptide hormone that is released in regions throughout the brain, including areas involved in food motivation. Animal studies suggest that oxytocin may reduce food intake. The effects of oxytocin administration on eating behavior in humans, which could have important implications in eating-related disorders ranging from obesity to anorexia nervosa, have not been investigated. This double-blind placebo-controlled cross-over study of single-dose oxytocin administration investigates whether:

1. Caloric intake will decrease following administration of oxytocin versus placebo
2. Appetite will decrease following administration of oxytocin versus placebo
3. Resting energy expenditure will increase following administration of oxytocin versus placebo

Inclusion Criteria:

• 18-45 years old
• BMI 18.5-24.9, 25-40
• Regular breakfast eater (at least 4 times per week)
• Stable weight within the past three months

Exclusion Criteria:

• Psychiatric disease
• Use of psychotropic medications
• History of eating disorder
• History of excessive exercise within the last three months
• History of diabetes mellitus
• Active substance abuse
• Hematocrit below normal range
• Gastrointestinal tract surgery (including gastrectomy, gastric bypass surgery, and small or large bowel resection)
• History of cardiovascular disease (such as hypertrophic cardiomyopathy, valvular heart disease, coronary heart disease, or coronary artery spasms)
• Untreated thyroid disease
• Tobacco use