Impact of Bariatric Surgery on the Gut Environment

To quantify protein assimilation after bariatric surgery, the investigators will perform in bariatric surgery patients (Roux-en- Y gastric bypass and Sleeve Gastrectomy) and in a control group a cross-sectional study with a single test day. On the test day, the study participants will consume a test meal that contains intrinsically labelled egg proteins and will take a capsule with 14C-glycocholic acid and a capsule with 3H-labelled polyethylene glycol. Participants will record a food diary 72h before and after the test day and during the test collect breath samples for 6h. Urine and stool will be collected respectively up to 24h and 72h after consumption of the test meal.

For the 1-year follow up study, the 3 patient groups (Roux-en-Y gastric bypass, Sleeve gastrectomy and control group with traditional weight loss therapy) will have 5 visits, a baseline visit and 4 visits after surgery or after starting traditional therapy. The time points after baseline include 2 weeks, 3 months, 6 months and 12 months. Each visit, a blood and stool sample will be collected, a 7-day food and stool diary will be registered and also weight loss will be recorded.

Inclusion criteria

• Surgery patients (toxicity and protein assimilation) : BMI > 40 kg/m² or > 35 kg/m² if combined with either obstructive sleep apnoea syndrome, high blood pressure not controllable with 3 different medications or type II diabetes, (3) exclusion of other underlying causes of obesity by an endocrinologist, (4) having tried to lose weight on a non-surgical way for at least 1 year without result and (5) a positive advice from a multidisciplinary team consisting of a surgeon, endocrinologist, psychologist and dietitian.
• Obese control group in weight loss program (toxicity) : obese but otherwise healthy patients on a weight loss diet (BMI > 30 kg/m²) in the context of the weight-loss program organised at the Obesity Clinic of University Hospital Leuven.
• Control group (protein assimilation) : normal weight (BMI 25-30 kg/m²) or overweight (BMI 25-30 kg/m²).

Exclusion criteria

• Intake of antibiotics 1 months before the start of the study. Pre-and probiotics, laxatives and anti-diarrhea drugs 2 weeks before the start of the study.
• Surgery patients and control group (toxicity) : Gastrointestinal disease or major abdominal surgery in the past (except from appendectomy and cholecystectomy).
• Surgery patients and control group (protein assimilation) : Lung, liver, kidney and gastrointestinal disease or major abdominal surgery in the past (except from appendectomy, cholecystectomy and bariatric surgery). Vegan, vegetarian, lactose-or gluten-free diet. Pregnant or lactating women and subjects who participated in the last year in a study with irradiation exposure.