 2. to compare the short-term 6-week and long-term 2 years effect of gastric bypass GBP and a very low calorie diet VLCD matched weight loss on bioavailability and pharmacokinetics of probe drugs caffeine, omeprazole, digoxin, midazolam, rosuvastatin, losartan and biomarkers and adjoining protein expressions for cytochrome P450 CYP1A2, CYP2C9, CYP2C19, CYP3A, P-glycoprotein gp and organic anion-transporting polypeptide OATP1B1. 