Lower Circulating Branched-Chain Amino Acid Concentrations Among Vegetarians Are Associated With Changes In Gut Microbial Composition And Function

Scope Vegetarian diets confer health benefits to many cardiometabolic diseases, although whether and how gut microbiota in vegetarians contributes to host metabolism remains unclear. Thus, the aim is to explore the possible links between the gut microbiota and circulating gut microbiota-host co-metabolites among vegetarians and omnivores. Methods and results Fecal and serum samples from 36 adults following a vegan, lacto-ovo vegetarian, or omnivorous diet are collected. A 16S rRNA gene, metagenome, metatranscriptome, and metabolome integrated multi-omics approach is adopted to profile fecal microbial composition and functionality and circulating gut microbiota-host co-metabolites. 16S rRNA gene and metagenomic sequencing suggest a significant difference in gut microbial composition between the two vegetarian groups and the omnivorous group at the family, genus, and species level. Metabolomic analysis reveals that circulating branched-chain amino acids (BCAAs)-valine, leucine, and isoleucine-are significantly lower in the two vegetarian groups than those in the omnivorous group. In line with the lower concentrations of BCAAs, metatranscriptomic analysis shows that the gut microbial pathway for the degradation of BCAAs is significantly upregulated among vegetarians compared with the omnivores. Conclusions The results indicate that gut microbiota plays an important role in the modulation of circulating BCAAs among vegetarians.