There is a paucity of literature on the impact of bariatric surgery on the conversion from pre-diabetes (PDM) to Type II Diabetes Mellitus (T2DM). The aim of this study was to evaluate the conversion to pre-diabetes to DM in bariatric surgery compared to a non-surgical cohort.


This retrospective study of morbidly obese patients with PDM patients who underwent Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) between 2001-2022. Non-surgical controls from a primary care cohort were propensity matched by hemoglobin A1c, age, sex, and BMI. DM was defined as a clinical diagnosis of T2DM or hemoglobin A1c>=6.5%. Kaplan-Meier analysis was used to estimate time until T2DM within bariatric patients. Cox regression was used to compare time until T2DM in RYGB versus SG and in bariatric surgery versus non-surgical controls.


We identified 1326 bariatric cases with PDM (n=1154 RYGB, n=172 SG). The cohort was 83% female, mean age=45.3, mean BMI=46.9 kg/m2, and median follow-up=7.2 years. The T2DM conversion at 5, 10, and 15 years postoperative was 1.8%, 3.3%, and 6.7%, respectively. The T2DM conversion was 20-times higher in matched non-surgical controls at 5, 10, and 15 years, 31.1%, 51.4%, and 68.7%, respectively (HR=19.8, 95% CI=[13.9-28.4], p<0.0001). When stratifying by surgery type, those with SG were 4-times more likely to convert to T2DM versus RYGB (HR=4.01, 95% CI=[1.71-9.39], p=0.0014).


Bariatric Surgery significantly decreases the conversion from pre-diabetes to T2DM. The impact of preventing conversion to T2DM was significantly higher for RYGB compared to SG.