Effect of Study Design on the Conclusions of Randomized Clinical Trials: Systematic Review and Meta-analyses on Sleeve Gastrectomy vs. Roux-en-Y Gastric Bypass on Weight Loss Outcomes after Metabolic Bariatric Surgery
In brief
Gastric bypass yields 3.6 points more total weight loss than sleeve surgery
Across four European trials involving 975 patients, Roux-en-Y gastric bypass produced 3.6 percentage points more total weight loss at five years than sleeve gastrectomy; excess weight loss was 8.5 points higher. The findings consistently favored bypass, but whether that difference is clinically important - or the procedures count as equivalent - depends on the trial's predefined hypothesis.
- Journal
- Obesity surgery (Q1)
- Published
- 30 October 2026
- Study design
- Systematic review / meta-analysis of RCTs
- Evidence level
- Level 1, High (CEBM 1a)
- Authors
- Saija Hurme, Kari Auranen, Eliisa Löyttyniemi, Paulina Salminen
- PMID
- 42957877
- DOI
- 10.1007/s11695-026-08993-8
Why clinicians should know about it
- Picked for Bariatric and Metabolic Surgery (paper of the day, 31 October 2026): Five-year randomized head-to-head sleeve versus bypass outcomes
Abstract
INTRODUCTION: Only a few randomized clinical trials (RCTs) have reported 5-year outcomes of sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) and they have used different study designs based on various hypothesis frameworks, including superiority, equivalence, and noninferiority. The aim of this study was to highlight the impact of study design on the interpretation of 5-year weight loss outcomes of SG versus RYGB. METHODS: PubMed, Embase and Cochrane databases were searched for RCTs comparing 5-year weight loss between SG and RYGB with follow-up rate exceeding 70% using percentage excess weight loss (%EWL) or percentage total weight loss (%TWL) through January 20, 2026. The revised Cochrane risk-of-bias tool for randomized trials (RoB 2) was used to assess the risk of bias. A pooled synthesis of weight loss was performed using a fixed-effects model and unstandardized mean differences were used to measure the effect size. RESULTS: Four European studies met the inclusion criteria with a total of 975 patients: two superiority trials and two equivalence trials. The risk of bias was assessed to be low in all four studies. The pooled estimates indicate that %EWL was 8.5 (95%CI 5.4 to 11.6) and %TWL 3.6 (95%CI 2.4 to 4.9) percentage points higher in RYGB compared with SG. CONCLUSIONS: The results across the four studies were highly consistent showing greater weight loss after RYGB compared with SG. Whether this difference should be interpreted as clinically relevant or whether the procedures may be considered equivalent depends on the predefined hypothesis.
Abstract as published, via PubMed.
For healthcare professionals. The summary is generated by AI from the published abstract, and the evidence level is assigned automatically from the study design on the Oxford CEBM hierarchy. Neither is medical advice. Read the full paper before changing practice.