Oxytocin is a peptide hormone produced in the brain that regulates food intake. However, the mechanisms for this effect in humans is not yet clear.

In this study, the investigators will therefore examine the effect of a single dose of intranasal oxytocin (compared to placebo) on levels of appetite-regulating hormones and functional magnetic resonance imaging activation of areas of the brain involved in food motivation.

Inclusion Criteria:

• Age 18-45 years old
• BMI 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 (having run more that 25 miles in any one week or having exercised more than ten hours in any one week)
• History of diabetes mellitus
• Active substance abuse
• Hematocrit lower than the 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
• Cardiac pacemaker, surgical aneurysm clips, neurostimulator, implanted pumps, metal fragments in body/eyes, nitroglycerin patch, severe claustrophobia