The purpose of this study is to determine whether the bile acid circulation is changed after gastric bypass surgery. Further, to account for how the changed anatomy of the gut influences how the bile acid and food is mixed in the gut and how this is associated with the changes in gut hormone release after the surgery.

Our hypothesis is that bile acid reabsorption from the gut is increased as animal models suggest so and bile acid blood concentration increases after surgery.

Inclusion Criteria:

• Age between 25 and 65 years
• For patients: uncomplicated Roux-en-Y Gastric Bypass surgery more than 12 months before study initiation
• For controls: Age, BMI and gender matched with patient group

Exclusion Criteria:

• Previous removal of gall bladder or other abdominal surgeries except appendectomy (and gastric bypass surgery for patient group)
• Known liver disease or thyroid disease requiring antithyroid medication
• Chronic gastrointestinal symptoms
• Any chronic disease interfering with, or susceptive of interfering with appetite or gastrointestinal function
• Any medication interfering with, or susceptive of interfering with appetite or gastrointestinal function
• Smoking within the last month
• Alcohol consumption above 168 grams per week
• Currently pregnant or breast-feeding
• Anaemia with haemoglobin <6,5 mmol/L (<117 mg/dl)
• Loss or gain of more than 3 kg within the last 3 months

Patients are recruited from the population undergoing gastric bypass surgery at Hvidovre Hospital (Denmark) Controls are recruited from www.forsoegsperson.dk (Danish webpage for recruitment of trial persons). Controls are recruited by advertisement.