Internal Synthesis
The body has the ability to make cholesterol on its own, via chemical synthesis. Cholesterol synthesis is primarily carried out by the liver and intestines. The synthesis of cholesterol begins with a compound called Acetyl CoA, which is made from the breakdown of any source of energy, including carbohydrates, fats, and sugars. Acetyl CoA then goes through a series of carefully controlled chemical reactions involving a number of enzymes (proteins that speed up chemical reactions) to be turned into cholesterol. One important step in this synthesis is the conversion of an intermediary, HMG CoA into another compound, called mevalonate. It is this reaction that is targeted by a type of cholesterol lowering drug called statins (such as Lipitor), which block the enzyme that makes this reaction possible.
Dietary Sources
Cholesterol can also be taken in via eating, where it can be absorbed by the intestines. The most abundant source of cholesterol in the diet is animal fat, which contains a mix of oils and lipids, including cholesterol. Beef, pork, poultry and shrimp are all major dietary sources of cholesterol, as well as cheese and egg yolks. Human breast milk also contains large amounts of cholesterol to help supplement the levels in infants. Almost all plant-based foods contain no cholesterol, unless they have been supplemented with cholesterol or cholesterol-containing compounds (such as animal fats).
Cholesterol Storage and Transport
Cholesterol is necessary for the body because it is an important part of the membrane that surrounds all cells. Cholesterol is also an important component of bile acids, which are excreted from the liver and are used to help digest fats and oils. Cholesterol is a lipid, which means that it cannot travel around in the blood on its own. Instead it is packaged inside of special proteins called lipoproteins. There are a number of different lipoproteins, but the most commonly known ones are low-density lipoprotein (LDL) and high-density lipoprotein (HDL). High levels of LDL have been implicated in an increased risk of cardiovascular disease, whereas high levels of HDL are thought to protect the body from cardiovascular disease.
