Dietary cholesterol absorption; more than just bile

Absorption of dietary cholesterol from the intestine is an important part o f cholesterol homeostasis and represents the first step that allows dietary cholesterol to exert its metabolic effects. Although the role of bile salt s in the initial absorption of dietary cholesterol, by the formation of emu lsions, is readily appreciated, the recognition that other molecular mechan isms might govern this process is only recently gaining momentum. Not only does the intestine regulate the amount of dietary cholesterol that enters t he body; it is very selective with regard to the sterols that are allowed i n. The human intestine is responsible for absorbing a significant amount of cholesterol each day. In addition to similar to0.5 g d(-1) of dietary chol esterol, many other sterols are also present in almost equal abundance in t he normal diet. Approximately 0.4 g of plant sterols, such as sitosterol, b rassicasterol and avanesterol, are also present. However, the human body se ems to allow only cholesterol to enter and remain in the body, with almost negligible amounts of plant sterols being retained. That specific molecular mechanisms are responsible for this behavior is supported by the identific ation of the genetic defect(s) in a rare disorder, beta -sitosterolemia (MI M 210250), where this process is disrupted. Such studies are now beginning to throw light on sterol absorption and excretion and elucidate the molecul ar mechanisms that govern these processes.