Figure 1.

The diagrammatic representation of the gut–liver axis. The gut–liver axis refers to the bidirectional communication between the gastrointestinal tract and the liver by the biliary tract, the portal vein, and systemic circulation. Through portal vein, liver mainly receives blood and nutritional supply, as well as gut-derived toxic factors. Probiotics and beneficial compositions from the gut can also protect liver through the gut–liver axis. Liver regulates the intestinal function and balance of gut microbiota through the bile acid.