The Role of Preoperative Weight Loss Interventions on Long-Term Bariatric Surgery Outcomes: A Systematic Review

Background/Objectives: The percentage of the world's population with Class II obesity (body mass index (BMI) ≥ 35) and above is increasing annually. Bariatric (elective weight-loss) surgery is performed for less than one percent of eligible patients. A recent Delphi was unable to reach a consensus recommendation for or against mandated weight loss targets prior to bariatric surgery. This systematic review, performed according to the PRISMA 2020 guidelines, looks at the literature to determine whether there is evidence that pre-operative weight loss affects long-term (≥5 years) outcomes of bariatric surgery (weight loss, co-morbidity resolution). Methods: MEDLINE, EMBASE, CABI Digital Library, and Cochrane Central Register of Controlled Trials (Central) were searched from 1 January 2000 to 1 March 2025. Twenty-one full papers were then assessed, and only three papers met the eligibility criteria for inclusion in this review. Results: 1072 patients were included (age range 26-73 years, sleeve: bypass 60.3%:49.7%, F:M 70.2%:29.8%). The studies differed in their pre-operative preparation and selection criteria for surgery: one paper used an intensive pre-operative information course and mandated 5% weight loss. This study reported a significant association between pre-operative weight loss and long-term outcomes. Two papers had no mandated pre-operative weight-loss target and found there was no association between pre-operative weight loss and long-term outcomes. Conclusions: There is limited and conflicting evidence that pre-operative weight loss percentage affects long-term outcomes of bariatric surgery. Further research looking at five-, ten-, and twenty-year outcomes for bariatric patients is required, particularly randomised controlled trials or tier one evidence.