Abstract
BACKGROUND: Obesity is increasingly prevalent in patients undergoing gastrointestinal (GI) cancer surgery and is associated with higher rates of intraoperative and postoperative complications. Preoperative weight loss has been proposed as a potential strategy to optimise surgical outcomes, but evidence regarding its safety, efficacy, and feasibility remains unclear. METHODS: A systematic search was conducted across MEDLINE, PubMed, EMBASE, and Cochrane from inception to 28th May 2025, following PRISMA 2020 guidelines and a registered protocol (PROSPERO ID: CRD42020154074). Eligible studies included adults (≥ 18 years) with obesity (BMI ≥ 30 kg/m²) undergoing surgery for GI cancers who received a structured preoperative weight loss intervention. Primary outcomes were feasibility and overall postoperative complication rates. Secondary outcomes included anastomotic leak, operative time, and adverse events. Meta-analysis was performed per outcome measure. RESULTS: Eight observational cohort studies comprising 532 patients (213 weight loss intervention vs. 319 control) were included. Completion rates for preoperative weight loss were ≥ 96.9%, with no intervention-related harms or surgical delays reported. Pooled analysis demonstrated a significant reduction in overall postoperative complications (OR 0.37, 95% CI 0.16–0.85; p = 0.02) and anastomotic leak (OR 0.26, 95% CI 0.12–0.60; p = 0.002) in the intervention group. Where assessed, skeletal muscle mass and nutritional parameters were preserved. CONCLUSION: Intentional preoperative weight loss appears feasible, safe, and may improve postoperative outcomes in patients with obesity undergoing GI cancer surgery. Integration of such strategies, particularly during neoadjuvant therapy windows, offers a modifiable opportunity to optimise surgical risk. Prospective trials are warranted to define optimal protocols, timing, and oncologic safety. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12029-026-01405-1.