Recent advances in the modulatory effects of kefir on the gut microbiota

Gut microbiota is critical for human immunity, metabolism, and overall well-being. Dysbiosis has been associated with a variety of diseases, including metabolic syndrome, inflammatory diseases, and neurodevelopmental issues. Kefir, a traditional fermented beverage produced with dairy or non-dairy substrates and kefir grains, contains probiotics and bioactive substances that may improve gut microbial composition. Current research indicates that kefir increases beneficial taxa such as Lactobacillus spp., Bifidobacterium spp., and Akkermansia spp., whereas decreasing pro-inflammatory microbes such as Enterobacteriaceae spp. and Clostridium spp. via antimicrobial metabolite production, competitive exclusion, prebiotic exopolysaccharides, short-chain fatty acid enhancement, immune modulation, and improved gut-barrier integrity. Furthermore, traditional kefir fermented with grains has higher microbial diversity and probiotic potential than kefir fermented with starting cultures. Despite these encouraging results, interpretation is constrained by variations in kefir production, dosage, intervention duration, and microbiota analysis methods; therefore, this review aims to evaluate how kefir modulates gut microbiota composition in human and animal models.