A meta-analysis of changes in gut microbiota structure following bariatric surgery

Bariatric surgery is a common intervention for obesity, yet its impact on gut microbiota remains unclear.

This systematic review and meta-analysis evaluated changes in gut microbiota composition before and after bariatric surgery.

We searched PubMed, Embase, Web of Science, and Cochrane Library up to October 2024 for randomized controlled trials (RCTs) and observational studies reporting pre- and post-surgery gut microbiota composition. Two reviewers independently screened studies, extracted data, and assessed bias using the Cochrane risk of bias tool and the Newcastle-Ottawa Scale (NOS). Primary outcomes included alpha diversity changes (Chao and Shannon indices), while secondary outcomes focused on relative abundance changes at phylum, family, and genus levels. Data were pooled using random-effects models.

Among 3670 screened articles, 45 were included, with 30 achieving NOS scores ≥7 and one trial having some concerns in the risk of bias assessment. Post-surgery, alpha diversity significantly increased but with high heterogeneity (Chao index: SMD 0.50, 95% CI 0.01-0.99, P = 0.046, I 2 = 87.3%; Shannon index: SMD 0.37, 95% CI 0.04-0.70, P = 0.028, I 2 = 90.2%). Meta-regression identified age and geographic region as heterogeneity sources. Both RYGB and LSG surgery increased the abundance of Akkermansia, Bacteroides, Streptococcus , and Veillonella , but the abundance of Bifidobacterium and Lactobacillus was reduced after LSG surgery.

Bariatric surgery significantly increases gut microbiota alpha diversity, with notable genus-level changes that indicate probiotic supplementation may be beneficial post-LSG. Owing to the high heterogeneity in taxonomic findings, further studies are needed to robustly establish the causal effects of specific surgical procedures on individual taxa.