Inclusion Criteria:  Patients with BMI > 40 kg/m2 or BMI > 35 kg/m2 associated with at least one comorbidity(s): hypertension, diabetes, cardiovascular disease, hyperlipidemia, sleep apnea, arthritis,hepatic steatosis. Candidates for RY gastric By-pass bariatric surgery, Over 18 and under 60 years of age For women of childbearing age: effective contraception implemented for at least 3 months. Failure of other medical cares (medical, nutritional, dietetic and psychotherapeutic treatment) well conducted for 6 to 12 months. Patient affiliated to a social security system (excluding AME) or entitled to benefits. Patient who agreed to participate by signing the informed consent of the study  Exclusion Criteria:  Pregnancy or breastfeeding in progress Severe psychiatric disorder or other illness that may disrupt the study follow-up or to invalidate the proper understanding of the protocol information and the informed consent Patient's foreseeable inability to participate in a clinical trial Severe and unstable eating disorders Patients with a contraindication to amino acid infusion Dependence on alcohol or psychoactive substances such as drugs Metabolic disease requiring a a low protein diet Known allergy to milk proteins Patient under guardianship or curatorship Patient under the justice protection Participation in another interventional research