The gastric bypass can reduce the bioavailability of food proteins. The bioavailability of hydrolyzed proteins may be higher than intact proteins. Thus, the use of hydrolyzed proteins could compensate for the decrease in protein bioavailability observed after gastric By-pass in morbidly obese patients.

The effectiveness of a hydrolyzed protein intake may be higher than that of an intact protein intake to improve the status of a By-pass.

The hypothesis would be that the use of hydrolyzed proteins would compensate for the decrease in bioavailability of food proteins caused by gastric By-pass.

Surgery is beneficial in terms of weight loss, correction of comorbidities and life expectancy but adverse effects can occur among which various nutritional deficiencies. Thus, in some cases, more or less marked protein undernutrition may be observed.

To overcome this protein undernutrition, protein supplements can be proposed. However, their effectiveness has not been satisfactorily assessed in this situation to date. Indeed, the protein malabsorption potentially induced by the By-pass limits its impact. The value of protein supplementation must also be considered in terms of overall efficacy, taking into account a possible decrease in spontaneous intake related to supplementation.

For the bioavailability studies, milk proteins will be presented in two different forms of the same origin: intact or hydrolyzed proteins. The proteins of the test meal are marked with 15N nitrogen.

For the three months daily supplementation period, the supplements will be intact proteins not marked with 15N nitrogen, provided to patients in the form of individual sachets. The purpose of this supplementation is to help the patient achieve the protein recommendations, which is 60 g/d.

Inclusion Criteria:

1. 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.
2. Candidates for RY gastric By-pass bariatric surgery,
3. Over 18 and under 60 years of age
4. For women of childbearing age: effective contraception implemented for at least 3 months.
5. Failure of other medical cares (medical, nutritional, dietetic and psychotherapeutic treatment) well conducted for 6 to 12 months.
6. Patient affiliated to a social security system (excluding AME) or entitled to benefits.
7. Patient who agreed to participate by signing the informed consent of the study

Exclusion Criteria:

1. Pregnancy or breastfeeding in progress
2. 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
3. Patient's foreseeable inability to participate in a clinical trial
4. Severe and unstable eating disorders
5. Patients with a contraindication to amino acid infusion
6. Dependence on alcohol or psychoactive substances such as drugs
7. Metabolic disease requiring a a low protein diet
8. Known allergy to milk proteins
9. Patient under guardianship or curatorship
10. Patient under the justice protection
11. Participation in another interventional research

all IPD that underlie results in a publication

The final report of the research will be drawn up and signed by the sponsor and the investigator.

A summary of the report drawn up according to the reference plan of the competent authority will be sent to the competent authority within one year so it will be sent on february, 2025, after the end of the research, corresponding to the end of the participation of the last person who is willing.

The access criteria IPD and any additional supporting information will be shared in the final report or publication. The analysis will be carried out on a modified intention-to-treat basis: all included patients, randomized and whose evaluation at 6 months after surgery will be available, will participate in the analysis in the group assigned by the random draw. This analysis avoids taking into account the patients who will be lost to follow-up before the evaluation at 6 months after the intervention. A per-protocol analysis will also be carried out. Changes in study weight, body composition, blood markers and food intake will be compared between groups using a mixed repeated measures model, with group as a fixed effect and time as the intra-repeat factor. topic. The group's effect on quality of life scores will be analyzed using a Wilcoxon test.