The PREBA Study: Effect of Preoperative Weight Loss With a 14-day Low-calorie Diet on Surgical Procedure and Outcomes in Patients Undergoing RYGB Surgery

Bariatric guidelines recommend preoperative weight loss of 5% to reduce the risk of surgical complications. However, results in the literature on the improvement of surgical procedure and outcomes are still conflicting. This study aims to evaluate the effect of preoperative weight loss by means of a 14-day low-calorie diet in bariatric patients on operative time, the ease of the Roux-en-Y gastric bypass (RYGB) procedure and long-term weight loss in a real-life experimental setting.

Inclusion Criteria: * Undergoing primary RYGB surgery (meeting all criteria + approval of surgeon) * Able to prepare the meal replacements at home Exclusion Criteria: * Undergoing another bariatric procedure than primary RYGB. * Diabetes Mellitus * Contraindication for the usage of Modifast meal replacements: * Allergy or intolerance to any substance in the used meal replacements (Soy, milk, gluten, egg, peanuts, nuts and seeds) * Veganism * Kidney failure (GFR \< 90 ml/min/1.73m2), liver failure or cardiac insufficiency * A heart attack (myocardial infarct) in the past twelve months * Cancer * Hypokalaemia: serum potassium level \