The aim of the study is to compare fasting and postprandial PYY levels between overweight/obese and lean subjects during and after an infusion of saline, PYY1-36 or PYY3-36 and to evaluate the efects on appetite, energy intake and energy expenditure.

The study is a randomised dobbelblinded placebo controlled study with 24 male subjects ( 12 lean and 12 overweight/obese subjects). VAS scores are used to assess appetite and two ad libitum meals are served in the hours following the infusion. Energy expenditure is measured by ventilated hood system and blood is sampled during part of the study day.

Inclusion Criteria:

• Normal weight (BMI: 18-23 kg/m2) or 12 overweight/obese (BMI: 27-40 kg/m2)
• Body weight fluctuations < 5 kg over the past 2 months.
• Blood pressure normal to mildly hypertensive (<159/99 mm Hg)
• Non-elite athletes and not planning to change physical activity during the study.

Exclusion Criteria:

• Any physiological or psychological illnesses that could influence the study results
• Regular use of medicine
• Smoking defined as <1 cigarette per day.
• Substance abuse or dependence.
• Blood donation within the past 3 months before entering the study
• Drinking >21 alcoholic units/week.
• Food allergies.
• Special diets (e.g. vegetarian) or dislikes to any of the foods served during the study.