Supplementary Material for: Association between the gut microbiota and depression in Asian populations: a systematic review and meta-analysis

Introduction Depression is a major global health concern. Emerging evidence implicates the role of the gut‒brain axis in the depression pathogenesis. However, the gut microbiota–depression association remains underinvestigated in Asian populations, where dietary habits, genetics, and environmental exposures differ from Western settings. This systematic review and meta-analysis assessed the association between gut microbiota and depression among Asians. Methods Five databases (PubMed, Embase, Scopus, Web of Science, and Cochrane) were searched through December 25, 2024. Observational studies comparing gut microbiota via sequencing in Asian individuals with depression versus healthy controls (HCs) were included. Data on α and β diversity and taxon-level differences were extracted. Standardized mean differences (SMDs) were computed for alpha diversity. Beta diversity and taxonomic findings were summarized narratively due to methodological heterogeneity. Results Of 2,557 records screened, 20 studies with 3,380 participants (1,298 depressed, 2,082 HCs) met inclusion criteria. Eighteen studies evaluated alpha diversity. A small but significant reduction in the Shannon index was detected among depressed individuals (SMD = –0.11; 95% CI: –0.19 to –0.02; p = 0.02), whereas other indices (Chao1, Simpson, ACE) revealed no significant differences. Among 16 studies examining beta diversity, 13 reported significant compositional differences. Phylum-level analysis consistently revealed increased Actinobacteria in depression, with variable trends in Firmicutes, Bacteroidetes, and Proteobacteria. Family-level trends included elevated Bifidobacteriaceae, Coriobacteriaceae, Enterobacteriaceae, and reduced Prevotellaceae, Rikenellaceae, and Veillonellaceae. Conclusions Gut dysbiosis is associated with depression in Asian populations, reflecting reduced beneficial taxa and increased proinflammatory microbes, with implications for microbial biomarkers and therapeutic targets.