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.
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.