the microbiota helps regulate energy balance, both by extracting calories from otherwise inaccessible components of our diet
and by controlling host genes that promote storage of the extracted energy in adipocytes (2-4). The
microbiota directs myriad biotransformations, ranging from synthesis of essential vitamins to the
metabolism of the xenobiotics that we ingest and the lipids that we produce (reviewed in ref. 1).
The microbiota modulates the maturation and activity of the innate and adaptive immune system:
an immune system educated to allow the host to tolerate a great degree of microbial diversity provides
a selective advantage since this diversity ensures the stable functioning of a microbiota in the
face of environmental stresses