Objective: Participating in a weight loss program before bariatric surgery is an established preparation tool in many specialized bariatric clinics. A certain amount of weight loss before surgery can even be a mandatory requirement for some clinics or insurance companies. The objective of this study is to investigate whether successful preoperative weight loss through adherence to a low-calorie diet three weeks prior to bariatric surgery could predict a difference in the duration of the procedure, intraoperative blood loss, need for revision, excess weight loss after 12 months and the participation in postoperative follow-up visits.