TAAR1 and irritable bowel syndrome: Its metabolites such as phenethylamine and tryptamine can activate trace amine-associated receptor 1 (TAAR1) on the enterochromaffin cells, stimulating the biosynthesis of serotonin, leading to the diarrhea-predominant irritable bowel syndrome (4) while other metabolites, e.g., glucorhamnan polysaccharides, can regulate the tumor necrosis factor TNFα secretion, modulating inflammatory responses (13, 14).