Intentional Preoperative Weight Loss for Obesity in Patients Undergoing Gastrointestinal Cancer Resections: A Systematic Review and Meta-analysis

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. 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. 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. 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.