Inclusion criteria, RYGB  Age > 18 years RYGB > 12 months prior to inclusion Weight stable (± 3 kg during the last month) HbA1c < 48 mmol/mol before surgery, and no history of diabetes HbA1c < 48 mmol/mol and fasting plasma glucose < 6.1 mmol/l at inclusion  Inclusion criteria, CON  Age > 18 years No former bariatric surgery Weight stable (± 3 kg during the last month) HbA1c < 48 mmol/mol, fasting plasma glucose < 6.1, and no history of diabetes  Exclusion criteria  Thyrotoxicosis or inadequately treated hypothyreosis Haemoglobin < 6.5 mmol/l at inclusion Pregnancy (pregnancy test in fertile woman before enrolment) or breast feeding Medication affecting the planned examinations which cannot be paused during the study period. Adherence to extreme diets with excessively high or low contributions from certain macronutrients (e.g. ketogenic diet) Complications restricting eating behavior (e.g. postprandial hypoglycemia, vomiting or strictures) MR contraindications