ObjectiveTo investigate the effects of single anastomosis sleeve ileal (SASI) bypass on weight loss, metabolic improvements, and postoperative safety in patients with obesity and its metabolic comorbidities (such as type 2 diabetes and hyperlipidemia). MethodsA retrospective analysis was conducted. The clinical data of patients with obesity [body mass index (BMI) ≥32.5 kg/m² or BMI ≥27.5 kg/m² with metabolic diseases] who underwent SASI bypass in the Nanjing Drum Tower Hospital Affiliated to Nanjing University Medical School from January 2023 to December 2023. Weight loss outcomes, including the percentage of total weight loss (%TWL), percentage of excess weight loss (%EWL), and percentage of excess BMI loss (%EBMIL), were recorded at 6 and 12 months postoperatively. Metabolic disease remission and complications at 12 months postoperatively were also documented. ResultsA total of 82 patients were included in the study. At 12 months postoperatively, the reductions in %TWL, %EWL, and %EBMIL were significantly greater than those observed at 6 months postoperatively [%TWL: (27.1±4.6)% vs. (23.6±3.8)%, t=2.379, P=0.026; %EWL: (72.1±5.8)% vs. (56.6±7.3)%, t=2.593, P<0.001; %EBMIL: (71.6±6.7)% vs. (58.3±4.9)%, t=2.607, P<0.001], remission was observed in 40 out of 48 patients (83.3%) with comorbid hypertension, 49 out of 51 patients (96.1%) with comorbid type 2 diabetes mellitus, and all patients with comorbid hyperlipidemia (33 cases) and obstructive sleep apnea syndrome (29 cases) achieved complete remission. Within 12 months after SASI bypass, 3 patients (3.7%) experienced melena, 2 patients (2.4%) developed incomplete intestinal obstruction, and 10 patients (12.1%) showed malnutrition. ConclusionThe findings of this study indicate that SASI bypass demonstrates significant weight loss and metabolic improvement effects in patients with obesity and metabolic diseases, with a controllable safety profile.