Association of Modest Preoperative Weight Loss and 30-Day Outcomes After Bariatric Surgery: A Contemporary MBSAQIP Analysis

Background Preoperative weight loss is commonly encouraged before bariatric surgery, yet its impact on short-term postoperative outcomes in contemporary practice remains uncertain. We evaluated the association between preoperative weight loss and 30-day postoperative outcomes using recent national registry data. Methods We conducted a retrospective cohort study using the 2020–2023 Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File. Patients with body mass index ≥ 35 kg/m² undergoing minimally invasive sleeve gastrectomy or Roux-en-Y gastric bypass were included. Preoperative weight loss was defined as a ≥ 2.0 kg reduction comparing the highest recorded weight within one year before surgery to the weight closest to the operative date, reflecting meaningful change beyond routine registry measurement variability. The primary outcome was 30-day serious postoperative complications, defined using the MBSAQIP bariatric surgical risk/benefit calculator composite. Multivariable logistic regression with robust standard errors was used. Prespecified sensitivity analyses included procedure-specific models, exclusion of robotic-assisted cases, and complete-case analysis for venous thromboembolism prophylaxis. Results Among 621,849 patients, 68.2% experienced preoperative weight loss. Preoperative weight loss was associated with lower adjusted odds of serious postoperative complications (adjusted OR 0.96, 95% CI 0.92–0.99). Weight loss was also associated with reduced venous thromboembolism (OR 0.88, 95% CI 0.78–0.98) and shorter postoperative length of stay (negative binomial incidence rate ratio 0.98, 95% CI 0.98–0.99). Findings were consistent across sensitivity analyses. Conclusions In a large contemporary national cohort, preoperative weight loss was associated with a statistically significant but modest reduction in serious postoperative complications and venous thromboembolism after bariatric surgery. These findings suggest that preoperative weight loss is associated with a modest incremental reduction in short-term postoperative risk but should not be used as the sole universal requirement for access to surgery. Trial registration Not applicable.