A 65-year-old man has been taking low-dose aspirin to reduce his risk of heart disease. He adds phytosterols to his daily regime for which of the following?
A. To reduce circulating triglyceride levels
B. To reduce circulating cholesterol levels
C. To reduce endogenous cholesterol synthesis
D. To decrease insulin secretion
E. To reduce fatty acid biosynthesis
The answer is B: To reduce circulating cholesterol levels. Phytosterols interfere with cholesterol absorption in the intestine (through blockage of cholesterol incorporation into the mixed micelles, which are necessary for intestinal epithelial cells to absorb dietary cholesterol), (figure-1), thereby leading to a reduction in circulating cholesterol levels.
Figure-1- Mechanism of cholesterol absorption.
Plant sterols and plant stanols are collectively known as phytosterols. Plant sterols are plant compounds with chemical structures similar to that of cholesterol. Especially high sterol levels are found in rice bran, wheat germ, corn oils, and soybeans.
Interestingly, phytosterols so closely resemble cholesterol that they can actually block food-based cholesterol from being absorbed into the bloodstream (Figure-2).
Figure-2- Role of phytosterols in the inhibition of cholesterol absorption. Sterols are structurally similar to cholesterol, hence inhibit their absorption.
The result is that both phytosterols and dietary cholesterol end up excreted in waste matter. The phytosterols do not interfere with the biosynthesis of cholesterol, nor do they alter the secretion of insulin. Phytosterols are also not capable of altering the rate of fatty acid biosynthesis, nor do they affect circulating triglyceride levels.
Studies have shown that daily phytosterols can lower these cholesterol measurements by an average of 10% to 14%. Because of these strong findings, the National Cholesterol Education Panel issued a new recommendation in 2001 that plant stanols and sterols be added to cholesterol-lowering regimens, along with the more traditional cholesterol-fighting tools, such as regular exercise, weight loss, and a low-fat diet.Please help Biochemistry for Medics by "CLICKING ON THE ADVERTISEMENTS" every time you visit us. Thank you!