Bile acids: The good, the bad, and the ugly

Bile acids, amphipathic end products of cholesterol metabolism, are "good" in the infant because they enhance lipid absorption and thereby promote gro wth. Bile acids also induce bile flow and biliary lipid secretion. The ente rohepatic circulation of bile acids is "bad" in the adult because it downre gulates hepatocyte low-density lipoprotein receptor activity and thereby el evates plasma cholesterol levels. Defects in bile acid metabolism such as i mpaired biosynthesis or transport are "ugly" because they cause morbidity a nd death. New approaches for treating these defects are being developed.