BILE ACID METABOLISM & ENTEROHEPATIC CIRCULATION

The Signalling System Connecting Your Liver, Gut, and Brain.

Bile acids — synthesised from cholesterol in the liver and stored in the gallbladder — were long regarded solely as fat-emulsifying detergents. The last decade of research has revealed them as sophisticated hormone-like signalling molecules that regulate glucose homeostasis, thyroid hormone activation, energy expenditure, microbiome composition, intestinal immune function, and even serotonin synthesis in the gut. Primary bile acids (cholic acid and chenodeoxycholic acid) are transformed by gut bacteria into secondary bile acids (deoxycholic acid and lithocholic acid) — a biotransformation that represents a critical interface between the liver and the microbiome. The farnesoid X receptor (FXR) and TGR5 receptor — activated by bile acids throughout the body — control pathways that govern insulin sensitivity, inflammatory responses, and mitochondrial thermogenesis in brown adipose tissue. Disruption of bile acid metabolism through gallbladder removal, antibiotic-induced microbiome damage, or liver dysfunction has systemic consequences that extend far beyond digestive discomfort.