Design: Open randomised controlled trial comparing, in obese patients after GBP, an additional oral intake of protein with or without a muscular-strengthening physical training programme (18 weeks) to standard medical and nutritional follow-up after bariatric surgery as control (3 groups). Primary outcome: Variation at 6 months after GBP in total and appendicular fat-free mass as assessed by dual-energy X-ray absorptiometry (DXA). Duration of the study: 36 months. Duration of participation for one patient: 7 months. Number of centers: Monocentric study.