Bile acids as signalling molecules
Bile acids are synthesized from cholesterol in the liver and released into the intestine to help emulsify dietary fats. Beyond digestion, they act as signalling molecules through two main receptors: the cell-surface receptor TGR5 (also called GPBAR1) and the nuclear receptor FXR (farnesoid X receptor).
FXR activation in the liver and intestine helps regulate bile acid synthesis through a feedback loop and influences glucose and lipid handling. TGR5 activation in tissues such as the gut, brown fat, and immune cells has been associated in research with energy expenditure and the release of the hormone GLP-1.
The gut microbiome connection
Gut bacteria chemically modify bile acids, converting primary bile acids made by the liver into secondary bile acids. This changes which receptors are activated and how strongly, creating a two-way relationship: bile acids shape the microbial community, and microbes reshape the bile acid pool.
This signalling network is an active area of metabolic research rather than a settled clinical tool. The diagram summarizes established receptor biology; it is educational and not a basis for treating any condition without professional medical guidance.