Many genomic studies have revealed associations between the gut microbiota composition and host meta- bolism. These observations led to the idea that a causal relationship could exist between the microbiota and metabolic diseases, a concept supported by studies showing compositional changes in the microbial community in metabolic diseases and transmissibility of host phenotype via microbiota transfer.

Accumulating data suggest that the microbiota may affect host metabolic phenotypes through the production of metabolites. These bioactive microbial metabolites, sensitive fingerprints of microbial function, can act as interkingdom signaling messengers via penetration into host blood circulation and tissues.

These fingerprints may be used for diagnostic purposes, and increased understanding of strain specificity in producing microbial metabolites can identify bacterial strains or specific metabolites that can be used for therapeutic purposes.