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Cholesterol is a fat-like substance called a lipid that is essential for human life. A component of every body cell, it helps to maintain the stability and fluidity of cell membranes. Cholesterol is also used in the liver to produce cholic acid, a major constituent of the bile fluid necessary for the digestion of fat. In addition, cholesterol is the material used by the body to build hormones such as estrogen and testosterone.

In addition, cholesterol is used in the skin to synthesize Vitamin D and to help control water evaporation through the pores.

Where Does Cholesterol Come From?

The body's cholesterol supply comes from two sources: food (approximately 400 mg a day for non-vegetarian North Americans - the National Cholesterol Education Program recommends 200 mg/day) and the body's own synthesis (approximately 1000 mg/day). The vast majority of dietary cholesterol comes from animal products, especially eggs, red meat and dairy products. Although some sources don't agree, plant food is not entirely cholesterol-free, although the amount found in plants is relatively insignificant. In the body, cholesterol is mainly manufactured in the liver, and to a lesser extent in several other organs.

The "Gut-Liver" Cycle Of Cholesterol - An Opportunity To Eliminate Cholesterol

The behavior of cholesterol in the gut is quite interesting: the body excretes a large amount of cholesterol (approx 1500mg a day) with the bile fluid during food digestion, only to reabsorb approximately 50% of it within the lower parts of the small intestine. The process is called the entero-hepatic (gut-liver) cycle because the bile comes from the bile-bladder which is part of the liver. Cholesterol can travel repeatedly throughout the body from the liver to the gut and back to the liver. Cholesterol that is not recycled during absorption is eliminated with the stool. Therefore, it is believed that the main function of the entero-hepatic cycle is to eliminate excess cholesterol.

 

1. Dietary cholesterol enters the small intestine and is absorbed into the bloodstream
2. Cholesterol is moved from the bloodstream to the liver
3. The liver secretes cholesterol back into the small intestine with the bile fluid

The fact that the entero-hepatic cycle eliminates cholesterol is important for two reasons. First, the amount of cholesterol circulating between the gut and liver is quite significant at approximately 2000mg a day (400mg from food + 1500mg from bile). Second, if we can prevent the reabsorbtion of cholesterol in the gut, more cholesterol is excreted with the stool and less is absorbed by the body. Therefore, we can theoretically eliminate even more cholesterol (up to 2000mg a day) than we ingest with food (approx 400mg a day). Preventing the reuptake of cholesterol in the small intestines is an obvious goal for medical intervention for individuals with high cholesterol. In fact, this is the exact function of the prescription drug ezetimibe (Zetia®), as well as phytosterols found in supplements.

Cholesterol In Your Blood

Since it is a fat-like substance, cholesterol is not water-soluble. This means it can't flow freely through arteries and veins. Instead, cholesterol quickly starts to form fatty droplets similar to grease drops in soup. The body's solution is to transport all lipids such as cholesterol and triglycerides in specialized cargo vehicles called the lipoproteins. The most well-known lipoproteins are LDL (low-density lipoprotein) and HDL (high-density lipoprotein) which we will discuss in our next article.

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