Proportional Single Anastomosis Sleeve Ileal (SASI) Bypass Based on Total Small Bowel Length: Optimizing Outcomes and Reducing Malnutrition

Introduction Single anastomosis sleeve ileal (SASI) bypass is a novel bariatric procedure typically performed with a fixed common limb of 250 cm. However, this approach may increase the risk of malnutrition. In this study, we modified the bypass length to 40% of the total small bowel length and evaluated the efficacy and safety of this proportional SASI technique. Methods In this study, patients with obesity who underwent proportional SASI between February 2023 and March 2024 were enrolled. Of 36 patients, 30 were included in the final analysis after excluding those with revisional surgery or loss to follow-up. The primary outcome was total weight loss (TWL) at 12 months. Secondary outcomes included changes in nutritional markers and postoperative complications. Results The cohort had a male-to-female ratio of 1:1, with a mean age of 40 years and mean preoperative BMI of 43.2 kg/m². The mean TWL was 30.0% at 12 months. Hemoglobin decreased slightly (14.1 to 13.7 g/dL, p = 0.121), while albumin remained stable at 4.3 g/dL. Significant improvements were observed in HbA1c (6.5% to 5.4%, p <0.001), triglycerides (207.0 to 83.3 mg/dL, p <0.001), and total cholesterol (181.8 to 153.7 mg/dL, p <0.001). The incidence of gallstone formation was 18.5%, while reflux esophagitis (grade B or higher) and marginal ulcers were both 8.7% at 1 year postoperatively. Conclusions SASI with proportional bypass appears to be an effective and safe procedure. It achieves substantial weight loss and metabolic improvement while maintaining nutritional stability.