Laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (LRYGB) are both effective surgical procedures to achieve weight reduction in patients with obesity. The trial objective was to merge individual-patient data from two RCTs to compare outcomes after LSG and LRYGB.

Five-year outcomes of the Finnish SLEEVEPASS and Swiss SM-BOSS RCTs comparing LSG with LRYGB were analysed. Both original trials were designed to evaluate weight loss. Additional patient-level data on type 2 diabetes (T2DM), obstructive sleep apnoea, and complications were retrieved. The primary outcome was percentage excess BMI loss (ëMIL). Secondary predefined outcomes in both trials included total weight loss, remission of co-morbidities, improvement in quality of life (QoL), and overall morbidity.

At baseline, 228 LSG and 229 LRYGB procedures were performed. Five-year follow-up was available for 199 of 228 patients (87.3 per cent) after LSG and 199 of 229 (87.1 per cent) after LRYGB. Model-based mean estimate of ëMIL was 7.0 (95 per cent c.i. 3.5 to 10.5) percentage points better after LRYGB than after LSG  (62.7 versus 55.5 per cent respectively; P < 0.001). There was no difference in remission of T2DM, obstructive sleep apnoea or QoL improvement; remission for hypertension was better after LRYGB compared with LSG (60.3 versus 44.9 per cent; P = 0.049). The complication rate was higher after LRYGB than LSG (37.2 versus 22.5 per cent; P = 0.001), but there was no difference in mean Comprehensive Complication Index value (30.6 versus 31.0 points; P = 0.859).

Although LRYGB induced greater weight loss and better amelioration of hypertension than LSG, there was no difference in remission of T2DM, obstructive sleep apnoea, or QoL at 5 years. There were more complications after LRYGB, but the individual burden for patients with complications was similar after both operations.