Long-Term (15-Year) Outcomes of metabolic bariatric Surgery in Obese Diabetic Patients: A Retrospective Cohort Study

Background Metabolic and Bariatric surgery is an established intervention for weight reduction and metabolic improvement in patients with obesity and type 2 diabetes mellitus (T2DM), particularly in the short (1–2 years) and medium term (up to 5 years). However, long-term outcomes beyond a decade remain poorly characterized. Objective To evaluate 15-year diabetes and weight related outcomes and the need for conversion surgery by primary procedure. Methods A retrospective cohort study was conducted at a single bariatric surgery center. Forty-nine obese diabetic patients who underwent primary bariatric surgery (Bypass, Sleeve, Band) between 2003 and 2007 were included. Preoperative and 15-year postoperative data were collected and compared for primary outcomes such as anthropometric measures, metabolic markers, obesity associated disease improvement and medication usage. Secondary outcomes included details, time, risk and predictors to conversion surgery. Statistical analysis included the Wilcoxon signed-rank test and McNemar’s test, with p < 0.05 considered statistically significant. Kaplan–Meier, log-rank, and Cox proportional hazard was performed to calculate secondary outcomes. Time-to-event analyses were performed in Python 3.12, all other analyses in IBM SPSS Statistics version XX. Results Among the 49 patients (median BMI: 52.6 kg/m2; range 38.6–69.4), primary surgeries included LRYGB (47%), LSG (33%), LGB (18%), and LDS (2%). Thirteen patients (26.5%) required conversional surgery. At 15 years, weight decreased significantly from a median of 143.0 kg to 101.65 kg (p<0.01), and BMI reduced from 52.6 kg/m2 to 39.55 kg/m2 (p<0.01). Significant reductions in medication requirements were also observed: oral hypoglycemic use dropped from 27 to 10 patients (p<0.01), insulin use fell from 6 to 3 patients (p<0.01), antihypertensive use reduced from 29 to 7 patients (p<0.01), and lipid-lowering agents dropped from 22 to 4 patients (p<0.01). Cardiac events decreased from 4 to 1 patient (p<0.01). The median HbA1c declined from 8.35% to 5.6%, and fasting glucose from 6.5 mmol/L to 4.55 mmol/L, although the sample size limited statistical significance for these biochemical markers. Reoperation-free survival at 15 years differed by procedure (log-rank P = 0.0018). Fifteen-year reoperation-free survival: Sleeve 25.0% (95% CI 5.7%–60.0%), Bypass 90.91% (95% CI 39.1%–99.2%), Band 25.0% (95% CI 3.1%–63.9%). In Cox models (reference Band), Bypass HR 0.10 (95% CI 0.01–0.96; P = 0.05) and Sleeve HR 1.93 (95% CI 0.47–7.92; P = 0.36). Median time to conversion was 2.34 years for Sleeve, 6.10 years for Band, and not reached within 15 years for Bypass. Conclusions Metabolic bariatric surgery provides sustained weight loss and significant long-term reductions in diabetes medication usage and obesity-associated disease over 15 years. At 15 years, procedure choice is associated with the risk of conversional surgery; Bypass appears more durable than Sleeve or Band. Larger prospective studies with Longitudinal long-term follow-up are needed to confirm these findings and examine biochemical outcomes in greater detail.