A two-center randomized clinical superiority trial of single-anastomosis sleeve ileal bypass versus sleeve gastrectomy for severe obesity: SASSY study protocol

BACKGROUND: Single-anastomosis sleeve ileal bypass is a novel metabolic bariatric surgery intended to enhance metabolic outcomes and reduce the risk of postoperative complications. Although preliminary outcome data for single-anastomosis sleeve ileal bypass are promising, evidence from adequately powered, randomized head-to-head comparisons is scarce. This trial compares the efficacy and safety of single-anastomosis sleeve ileal bypass versus sleeve gastrectomy in patients with class II obesity (body mass index = 35.0-39.9 kg/m²) with at least one obesity‑related comorbidity or class III obesity (body mass index ⩾40.0 kg/m²). METHODS: This two-center randomized clinical superiority trial enrolls patients eligible for metabolic bariatric surgery at two specialized Norwegian centers. Included patients are randomly assigned (1:1) to either single-anastomosis sleeve ileal bypass or sleeve gastrectomy with standardized perioperative treatment and care. The primary endpoint is the between-group difference in change in body mass index from baseline to 2 years after single-anastomosis sleeve ileal bypass versus sleeve gastrectomy. Secondary endpoints include additional weight loss outcomes, the prevalence of gastroesophageal reflux disease, surgical and postoperative complications, obesity-related comorbidities, nutritional status, bone mineral density, gastrointestinal symptoms, quality of life, and rates of revisional and conversion surgery. All endpoints will be evaluated at 2 and 5 years after surgery. Statistical analyses utilize linear mixed models and analysis of covariance within an intention-to-treat framework. DISCUSSION: This trial will provide high-level evidence with robust and comparative outcome data on single-anastomosis sleeve ileal bypass and sleeve gastrectomy, aiming to clarify the clinical utility of single-anastomosis sleeve ileal bypass and inform surgical practice. Findings will address gaps in medium- and long-term evidence regarding weight loss, safety, comorbidity resolution, and quality of life following single-anastomosis sleeve ileal bypass.