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.

Metabolic bariatric surgery (MBS) can lead to substantial fat-free mass loss due to malnutrition, decreased protein intake and insufficient physical activity.

• Disproportional fat-free mass loss (FFML) has been associated with an increased risk for adverse health outcomes.
• Resistance training combined with protein intake contributes to maintenance and increase of fat-free mass in healthy individuals.
• It is unclear whether RT and protein supplementation can prevent FFML after MBS, motivating the trial.

The ENRICHED trial will randomise 400 patients scheduled to undergo MBS in a 1:1 ratio to the intervention or control group.

• The study is recruiting participants at two centres in the Netherlands: Nieuwegein and Amsterdam.
• The intervention group receives the ENRICHED perioperative care programme; the control group receives the standard perioperative care programme of the Dutch Obesity Clinic.
• The postoperative standard programme consists of 13 group sessions spread over a period of 18 months.
• The study protocol V.2.0 was approved by the Medical Research Ethics Committee Oost-Nederland (NL-OMON57119) on 9 April 2025.
• The trial is registered as NCT07156552.

The ENRICHED intervention includes resistance training beginning 3 weeks after MBS, comprising both home-based and supervised sessions.

• Home-based resistance training sessions are performed two to three times a week.
• Supervised resistance training sessions are 45–60 minutes in duration, performed once weekly.
• Resistance training intensity is set at 60–75% of one-repetition maximum (1-RM).

Protein supplementation in the ENRICHED intervention begins with 20 g of whey protein daily and is gradually increased to 60 g per day.

• Protein supplementation starts 3 weeks after MBS by adding 20 g of whey protein to the daily intake.
• The supplementation is gradually increased with 20 g every 4 weeks until a total of 60 g whey protein per 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 fat-free mass loss, defined as FFML/total weight loss ≥30%, at 3 months post-MBS.

• Secondary endpoints include 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.
• The study aims to provide evidence for a patient-tailored intervention that could be implemented in clinical practice.