Phenotypical Approach of the Drug Metabolizing Hormones Activity Before and After Roux-en Y-Gastric Bypass

Principal Judgement criteria : Phenotypical markers of enzymes and transporter activity before, at 5-8 weeks and 25-30 weeks following surgery. Secondary judgement criteria : * Genetic polymorphisms known to affect expression and/or activity of enzymes and transporter. * Intestinal and hepatic expression and activity of the enzymes and transporter of interest. * Markers of inflammation Methodology, study design : open-labelled monocentric study. Sample size : It will be a descriptive experimental study involving 12 subjects. Study design : In centre 1: Inclusion at least 2 weeks prior to surgery (V0) In centre 2: Three studies of 12 hours each will occur (in addition with the usual clinical and surgical follow up) at three times periods: in the 8 weeks period before surgery (V1), at 5-8 weeks after surgery (V2) and at 25-30 weeks after surgery (V3). In centre 3: the patients will undergo gastric bypass surgery (corresponding to the usual clinical and surgical follow up) and samples of jejunum and liver will be obtain during the surgery (J0). Centres 4 and 5 are involved in samples analysis.Hence, patients will attend 3 visits, in addition to the usual clinical and surgical follow-up. Study duration: 26 months (with duration of inclusion of 18 months) Duration for a patient: 38 weeks at maximum (8 months) Investigating center and participating units: one center enrolling the patients and three centers involving in the others investigations.