In this protocol, the investigators propose a randomised controlled trial to explore the effects of intra-nasal oxytocin administration on appetite regulation. The investigators will run a cross-over design with 60 healthy adult men.

Inclusion Criteria:

• Gender: Male
• Age: 21-45 years
• Normal weight: Body mass index of 18.5 to 22.9
• Have had a stable weight for the past 3 months (less than 5kg)
• Have regular breakfast meals (≥ 4 times a week of self-reported consumption of a breakfast meal)
• Have habitual sleep of 6.5-8.5 hours
• Have English as first language (or fluent in spoken and written English)

Exclusion Criteria:

• Symptoms / history of any major medical condition, including:

  • Bariatric surgery or surgical obesity treatment
  • Diabetes
  • Cardiovascular disease
  • Thyroid disease
  • Anaemia
  • Psychiatric disorders
  • Eating disorders

• Excessive exercise (running > 40 km or exercising > 10 hr in a week)

• Currently on a special diet or trying deliberately to restrict food intake

• Currently on a weight loss program

• Smoking or substance abuse

• Use of medications that can affect weight (e.g., steroids, approved weight-loss drugs)