STANFORD, Calif. — Patients seeking weight-loss treatments can rest easier regarding one of the more sensitive potential side effects of obesity interventions. A comprehensive cohort study conducted by researchers at Stanford Health Care found no statistically significant difference in the risk of developing new-onset fecal incontinence between patients taking GLP-1 receptor agonists and those undergoing bariatric surgery.
The research team, led by Dr. Rachel Colbran in the Department of General Surgery, analyzed electronic health record data from more than 13,800 adults treated between 2015 and 2025 who had obesity and no prior history of bowel control issues.
The study evaluated 12,284 patients who initiated popular GLP-1 medications—such as semaglutide and tirzepatide—and compared them against 1,540 patients who underwent bariatric surgical procedures, including gastric bypass and sleeve gastrectomy.
Key Findings:
- Equal Long-Term Safety: After applying propensity score matching to account for baseline health differences, researchers discovered that rates of new-onset fecal incontinence were statistically non-significant between both groups at both the 1-year and 5-year post-treatment marks.
- Body Mass Index (BMI) Trajectory: Patients in the GLP-1 group had a significantly higher average BMI at one year compared to the surgery group ($41.5$ vs. $31.4$). However, by year five, the mean difference in BMI between the two cohorts narrowed and became statistically non-significant.
- Baseline Health Differences: Prior to matching, patients prescribed GLP-1 medications were generally older (mean age $53.4$ vs. $44.9$) and presented with higher initial rates of complex conditions, such as diabetes with complications ($19.7\%$ vs. $3.0\%$) and renal disease ($13.0\%$ vs. $3.0\%$).
The findings provide crucial data for clinicians and patients evaluating non-surgical versus surgical weight-management pathways, confirming that choosing a pharmaceutical intervention over surgery does not elevate the long-term risk of developing severe lower gastrointestinal complications.
