Cholesterol in the body is thought of as originating solely from the diet through absorption from the gut. However, the reality is that most of the cholesterol is not sourced from food but rather manufactured within the body. Dietary cholesterol or exogenous cholesterol is absorbed from within the intestines. Endogenous cholesterol sourced within the body is synthesized in the liver. It is sometimes commonly referred to as liver cholesterol. Triglycerides on the other hand are primarily sourced from the diet, especially in saturated fats and also synthesized from excessive unused calories as is seen with high carbohydrate diets.
Production of Liver Cholesterol
Cholesterol is synthesized in the liver by combining several molecules of acetyl co-enzyme A (acetyl-CoA). This compound is sourced from breaking down fats like triglycerides. Therefore triglycerides contributes to cholesterol production in the liver. Triglycerides in turn are sourced from saturated fats as well as by converting excess carbohydrates and proteins.
Despite the often negative light in which cholesterol and triglycerides are portrayed in, the reality is that the body needs these lipids. It is used for energy production, waste elimination through bile, hormone production and also for structural needs like cell membranes. However, the problem arises when these lipids are in excess within the body and certain types like atherogenic LDL-cholesterol is able to clog arteries. Read more on Lipoproteins.
Liver Breaks Down Cholesterol
Although it has been highlighted that the liver synthesizes most of the cholesterol in the body (endogenous cholesterol), it also plays an important role in breaking down cholesterol. This is done through bile which is formed in the liver, stored in the gallbladder and passed into the gut in response to certain foods like fats. It is eventually passed out of the gut in the stool.
Despite the body’s efficienct mechanisms for maintaining homeostasis, not all cholesterol can be adequately eradicated. Therefore dietary management and the use of medication like statins are necessary to reduce and control the blood cholesterol. There are several other modifiable and unmodifiable factors that also play a role in high blood cholesterol beyond dietary intake.
Cholesterol in the Bile
Cholesterol in the bile exists in the form of bile acids, cholesterol and lecithin (a type of phospholipid which is another lipid). Through its chemical interaction with other bile constituents like bilirubin, the lipids are passed out in bile. However, when the quantity of cholesterol exceeds the solubilizing capacity of bile, it can lead to biliary sludge and gallstones. Once passed into the gut, it helps to emulsify fats and is eliminated in the stool. However, some degree of reabsorption can occur within the intestine meaning that the lipids passed out with bile can reenter the system before its removed from the body during defecation.
In this regards, the cycle can continue and this highlights the importance of dietary control and lifestyle factors in managing high blood cholesterol levels. Read more on :
Article reviewed by Dr. Greg. Last updated on April 21, 2011