SADI-S Versus Distal OATB (SASI): Does the Duodenal Pathway Matter in Ileal-Level Single-Anastomosis Surgery?

Background: Single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SG) (SADI-S) and distal one anastomosis transit bipartition (dOATB) represent two distal single-anastomosis metabolic procedures sharing similar anatomical configurations but differing fundamentally in their approach to duodenal transit. Both combine SG with an omega-loop anastomosis to the distal ileum approximately 250–300 cm from the ileocecal valve. However, SADI-S positions the anastomosis on the duodenal bulb, achieving complete duodenal exclusion, while dOATB performs a prepyloric antral anastomosis, preserving duodenal transit through a bipartition mechanism. This fundamental difference raises a critical question: Does complete duodenal exclusion matter for metabolic outcomes in distal intestinal procedures? Methods: We conducted a narrative review comparing anatomical, physiological, and clinical aspects of SADI-S and dOATB, emphasizing the role of duodenal exclusion in weight loss (WL), metabolic improvements, and nutritional consequences. We examined the hypotheses to provide a theoretical framework for understanding these procedures. Results: Both procedures demonstrate excellent WL, with total WL ranging from 35% to 45% and excess WL exceeding 80% at medium-term follow-up. Type 2 diabetes remission rates are remarkably high in both groups (85%–95%). SADI-S has a more extensive evidence base with longer follow-up and IFSO and ASMBS endorsement. Distal OATB, while demonstrating comparable metabolic efficacy, offers theoretical advantages in nutritional preservation through maintained duodenal transit and facilitated endoscopic access to the biliopancreatic system. The holoileum hypothesis suggests that adequate ileal stimulation through an elongated common channel may be more important than duodenal exclusion per se . Conclusions: Current evidence suggests that excellent metabolic outcomes can be achieved with distal single-anastomosis procedures regardless of duodenal exclusion status. The elongated common channel and ileal stimulation appear to be the critical determinants of metabolic success. Distal OATB may offer advantages in nutritional preservation and endoscopic accessibility while maintaining comparable metabolic efficacy. Prospective randomized trials directly comparing these procedures are warranted.