Cholesterol is involved in cell membrane structure and is a precursor for synthesis of bile acids and steroid hormones. Over-production, or stockpiling of cholesterol in the body, can occur if regulating processes fail or are unable to balance the combination of dietary cholesterol and cholesterol manufactured by the body. Excess cholesterol is deposited, among other places, in the coronary arteries, and the resulting atherosclerosis can lead to cardiovascular disease.
Dietary Cholesterol
Dietary cholesterol raises total cholesterol and low density lipoprotein (LDL, or "bad" cholesterol), but less than the effect of saturated fatty acids. Foods high in cholesterol include egg yolks, meat, milk and milk products such as butter and cheese.
Cholesterol Made by the Body
Cholesterol is often demonized as a bad thing in bad food, but it is actually a compound the body makes and uses for important functions. The liver makes cholesterol from fragments of carbohydrates, protein and fat.
Regulating Cholesterol Synthesis
The liver can make 800mg to 1,500mg of cholesterol per day, but more than enough cholesterol is provided in the diets of most people. The extent to which dietary intake of cholesterol modifies blood cholesterol level varies based on genetic tendencies. If the body is unable to regulate the total amount of cholesterol by compensating for dietary intake, harmful deposits in the artery walls may take place and lead to atherosclerosis.
Enterohepatic Circulation of Cholesterol
Bile is made in the liver, stored in the gallbladder and released into the small intestine when needed to aid digestion by emulsifying fat. Most of the bile released into the small intestine is reabsorbed and recycled back to the liver to be reused by the body. This cycle is called enterohepatic circulation of bile.
Bile Acids and Cholesterol
Some bile escapes enterohepatic circulation and is trapped by dietary fibers in the colon and excreted as waste. Thus, bile acids made by the liver are a way for the body to get rid of cholesterol. However, bile acids cannot compensate for an excess intake of cholesterol in the diet.
Treatment of High Cholesterol (Hypercholesterolemia)
The first steps to reduce risks associated with high levels of cholesterol are to modify the diet and increase physical activity. High intake of saturated fat contributes the most to high LDL. Therapeutic lifestyle changes to lower cholesterol include reducing saturated fat to less than 7 percent of total calories, reducing dietary cholesterol to less than 200mg per day, adding 2g per day of plant stanols/sterols and 10g to 20g of soluble fiber per day, increasing physical activity and managing weight.
If diet and exercise fail to lower cholesterol sufficiently, lipid-lowering drugs may be prescribed. Medications to reduce cholesterol include statin drugs, which work by blocking the action of the enzyme HMG-CoA, a key step in the body's process of synthesizing cholesterol. Other lipid-lowering drugs include bile acid sequestrants, nicotinic acid and fibric acids. An alternative dietary supplement, red yeast rice, is a statin-like compound.
References
- "Nutrition Through the Life Cycle"; Judith E. Brown; 2008
- "Understanding Nutrition"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2002
- Medical Biochemistry Page: Introduction to Cholesterol Metabolism
