Background/Aims: Evidence suggests that socioeconomic position (SEP) may shape the gut microbiota, representing a mechanism through which social and environmental factors may drive health inequalities, yet no systematic review has examined this association. In a narrative systematic review, we searched PubMed, Web of Science, and Scopus up to 30 November 2024 for observational studies examining associations between measures of SEP and gut microbiome diversity, composition, or function in participants of any age, ethnicity, or location.

Conclusions: We identified 1,479 unique studies, of which 26 met the inclusion criteria for this review. Associations were observed between SEP indicators and gut microbiome features, including alpha and beta diversity, taxonomic composition, and functional pathways. Notably, socioeconomic patterns in alpha diversity differed by context, with greater diversity observed in advantaged groups in high-income countries but in disadvantaged groups in low- and middle-income countries. Differences in beta diversity suggest that advantaged and disadvantaged groups have distinct gut microbiome profiles. Furthermore, considerable heterogeneity was evident across studies, particularly in sampling, sequencing, and analytical methods. Overall, socioeconomic-related differences in the gut microbiome are evident globally, highlighting the microbiota as a potential target for interventions to reduce disparities. Further research using larger, more diverse cohorts, metagenomic sequencing approaches, and comprehensive measurement and adjustment of key covariates can deepen our understanding of this relationship.