This double blind randomized placebo controlled trial investigates the effect of protein supplementation on fat free mass loss in patients who underwent a Roux-en-Y gastric bypass.

Rationale: Protein malnutrition is a severe complication of bariatric surgery and leads to increased morbidity. Previous studies have shown that protein intake and physical activity are the most important factors in the preservation of fat free mass during weight loss. Low protein intake is very common in patients undergoing bariatric surgery despite dietary counselling. Protein powder supplements might help patients to achieve the protein intake recommendations after bariatric surgery and could therefore contribute to preserve fat free mass.

Objective: The main aim of this study is to assess the effect of a daily consumed clear protein powder shake during the first six months after bariatric surgery on fat free mass loss in the first twelve months after laparoscopic Roux-en-Y gastric bypass (LRYGB).

Study design: Double-blind randomized placebo-controlled intervention study

Study population: Patients undergoing LRYGB at the bariatric expertise center for obesity of the Maasstad Hospital Rotterdam.

Intervention and procedure: Inclusion will take place at the outpatient clinic of the bariatric expertise center for obesity of the Maasstad Hospital. Patients will be randomly assigned to either the intervention or control group before surgery. The intervention group will receive a clear protein powder shake of 200 ml containing 20 grams of whey protein which should be taken daily during the first six months after LRYGB. The control group will receive an isocaloric, clear, placebo shake containing maltodextrine.

Main study parameters/endpoints: The main study parameter is the percentage fat free mass loss six months after surgery, calculated as fat free mass loss (kg) divided by total weight loss (kg) x 100%. Fat free mass will be assessed by multi-frequency bioelectrical impedance analysis (MF-BIA). Secondary parameters are percentage fat free mass loss, total weight loss, fat mass loss, BMI, hand grip strength, total protein intake and its progression over time, measured at baseline, 3, 6 and 12 months of follow-up.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: No additional outpatient visits will be required for study participants. A three day food diary and physical activity questionnaire must be filled out by all study participants at five regular follow-up moments. Body composition and handgrip strength will be assessed during these visits. All study participants will be asked to drink a daily shake, either protein or placebo, integrated in their postoperative diet. Study participants will receive information about the changes in body composition after surgery which is considered to be a significant benefit for patients participating in this study. The risk of participation is considered low. The risk consists of a possible allergic reaction to either the protein shake or the placebo.

Inclusion Criteria:

• - Scheduled for a laparoscopic Roux-en-Y Gastric Bypass
• Age 18 - 65 years
• Body Mass Index ≥ 35 with the presence of severe comorbidity related to morbid obesity (diabetes mellitus type 2, obstructive sleep apnoea syndrome (OSAS), hypertension, etc.) or a BMI ≥ 40 with or without the presence of severe comorbidity related to morbid obesity
• Written informed consent

Exclusion Criteria:

• - Revisional bariatric surgery
• A protein-restricted diet for medical reasons
• Diagnosis of a (neuro-) muscular disease
• Inability to undergo MF-BIA (i.e. pregnancy, pacemaker)
• Allergy to any of the ingredients of either the protein or the placebo shake

Study products (protein or placebo drinks) are provided to study participants. Study product is marked by a unique batch number, corresponding to protein or placebo in the ingredients list.