Long-term adherence to plant-based diets can modify gut bacterial microbiota composition and metabolite profiles, which may be particularly relevant for postmenopausal women who frequently adopt such diets and experience age-related changes in nutrient absorption and metabolism. Fermented foods, commonly consumed in vegetarian diets, enhance dietary diversity and nutritional quality. This study compared gut bacterial microbiota and fecal metabolomes between vegetarians (VGs) and omnivores (OMs) and evaluated the contribution of fermented food intake. Thirty-two healthy postmenopausal Thai women (>55 years; 16 VGs, 16 OMs) were enrolled. Gut bacterial microbiota and fecal metabolites were analyzed using 16S rRNA metagenomic and untargeted ¹H-NMR metabolomics. The five most frequently consumed fermented foods were microbiologically characterized. Fermented food consumption was found to be significantly different between groups. OM participants reported infrequent consumption (60% of weekly meals). VG participants exhibited enrichment of Prevotella, Faecalibacterium, and Blautia, while OM participants showed higher abundances of Bacteroides and Escherichia–Shigella. LEfSe identified Weissella as a bacterial taxon associated with the VG group. Functional prediction and metabolomic analyses indicated enhanced carbohydrate fermentation and increased short-chain fatty acid (SCFA) production in VGs, whereas OM profiles reflected greater protein catabolism. Fermented foods consumed by VGs shared microbial biomarkers with the VG gut bacterial microbiota and were rich in SCFAs and essential amino acids, supporting their potential role as microbial and metabolic contributors within the gut ecosystem and nutritional adequacy in postmenopausal vegetarians.