Fig. 1From: Review: microbial transformations of human bile acidsDiversity of known human bile acids. A All BAs are built off the same sterol backbone with variations in hydroxylated positions, hydroxyl orientation, and the presence of ketones. CA and CDCA, along with GlyCA, GlyCDCA, TaurCA, and TaurCDCA, make up the primary BA pool. Remaining BAs in the list make up secondary and tertiary BA pools as a result of modifications from gut microbes [5,6,7]. Allobile acids, although matching in hydroxyl positions to their standard bile acid counterparts, differ in ring orientation. Standard bile acids have the first ring in the B transorientation, yielding 5β-BAs, while allobile acids have this ring in the C cis-orientation, yielding 5α-BAsBack to article page