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. Methods: All cases that underwent sleeve gastrostomy or Roux-en-Y gastric bypass in a bariatric department in Germany between January 2018 and October 2019 were retrospectively evaluated for our study. Data were obtained on gender, age, BMI, weight before and after preoperative weight loss, weight after 1, 3, 6, and 12 months, operative times, haemoglobin and haematocrit one day before and two days after surgery, the need for revision 4 weeks after the procedure, and the number of follow-up visits. Groups were formed according to the achieved excess weight loss before surgery and analysed inter alia using Kruskal Wallis H Test