Effectiveness of protein supplementation combined with resistance training to counteract disproportional fat-free mass loss following metabolic bariatric surgery: rationale and design of the ENRICHED randomised controlled trial.

introductionMetabolic bariatric surgery (MBS) can lead to substantial fat-free mass loss (FFML) due to malnutrition, decreased protein intake and insufficient physical activity. Disproportional FFML has been associated with an increased risk for adverse health outcomes. Resistance training (RT) combined with protein intake contributes to maintenance and increase of fat-free mass (FFM) in healthy individuals. However, it is unclear whether RT and protein supplementation can prevent FFML after MBS. METHODS AND ANALYSIS: In the EffectiveNess of pRotein supplementatIon Combined witH resistance Exercise training to counteract Disproportional fat-free mass loss following metabolic bariatric surgery (ENRICHED) randomised controlled trial, 400 patients scheduled to undergo MBS will be randomised in a 1:1 ratio to the ENRICHED perioperative care programme (intervention group) or the standard perioperative care programme of the Dutch Obesity Clinic (control group). The study is currently recruiting participants at two centres in the Netherlands: Nieuwegein and Amsterdam. The postoperative standard programme consists of 13 group sessions spread over a period of 18 months. As part of the ENRICHED programme, RT and protein supplementation will be added 3 weeks after MBS. Additional whole-body RT consists of home-based training sessions two to three times a week, and supervised RT sessions of 45-60 min once weekly, performed at 60-75% of one-repetition maximum (1-RM). Protein supplementation will start by adding 20 g of whey protein to the daily intake. The supplementation will be gradually increased with 20 g every 4 weeks until a total of 60 g whey protein a day is reached. After 12 weeks of protein supplementation, the focus shifts towards incorporating protein-rich food products into the daily dietary intake. The primary endpoint is the prevalence of disproportional FFM loss, defined as FFML/total weight loss ≥30%, at 3 months post-MBS. Secondary endpoints are differences in body composition, muscle strength and function, cardiorespiratory fitness, (cardio)metabolic health, health-related quality of life, gastrointestinal discomfort, cost-effectiveness of the intervention and treatment satisfaction. Outcomes will be assessed preoperatively and at 3, 6 and 12 months postoperatively. ETHICS AND DISSEMINATION: The study protocol V.2.0 was approved by the Medical Research Ethics Committee Oost-Nederland (NL-OMON57119) on 9 April 2025. All participants will provide written informed consent prior to enrolment. Study findings will be disseminated through peer-reviewed publications and conference presentations. Insights gained in this study will provide evidence for a patient-tailored intervention that could be implemented in clinical practice. TRIAL REGISTRATION NUMBER: NCT07156552.