CHolesterol
Cholesterol chemistry
Cholesterol is a waxy, 27 carbon compound that consists of a hydrocarbon tail (or side chain), a central sterol nucleus made of four hydrocarbon rings, and a hydroxyl group. Hydrocarbon is a carbon and a hydrogen atom bonded together and hydroxyl is an oxygen bonded to a hydrogen atom. Both the hydrocarbon tail and the steroid nucleus are nonpolar. This means the electrons are equally shared between atoms, making the net charge of the structure fairly neutral. This is unlike a polar substance, where there is a significant difference in charge within a structure. To learn more about the structure of the atom and bonding, see "Elements, Atoms & Ions". Water is polar, so it does not mix with cholesterol, which is nonpolar. This is what gives cholesterol characteristics of fat. Polar does not interact with nonpolar (why oil and water separate), but they will interact with their own kind. All this is why cholesterol (lipid) needs to be packaged with proteins to be carried through the blood, which contains a lot of water. Without the polarity of the protein, the cholesterol would separate from the blood and would be unable to circulate through it. This lipid plus protein is called a lipoprotein.
How does cholesterol affect the body?
There is a certain misconception that cholesterol is harmful in itself. However, it is needed to maintain cell structure and to create vitamins and hormones. Cholesterol comes from 2 sources. The primary source is your liver, which makes all the cholesterol that is necessary for your body. The rest (dietary cholesterol) can come from foods from animals.
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More than the dietary cholesterol, the types of fat you consume is what determines LDL and HDL levels. That's why experts agree that when looking at nutrition labels, focusing on trans, saturated, and unsaturated fat levels, rather than the cholesterol is more helpful. Studies have shown that for most people, the amount of cholesterol eaten has only a modest impact on the amount of cholesterol circulating in the blood. But for a few people, blood cholesterol levels rise and fall very strongly in relation to the amount of cholesterol eaten.
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When unsaturated fats are eaten instead of saturated and trans fats, it can lower LDL and even raise HDL. On the other hand, saturated fats actively raise LDL by inhibiting LDL receptor-mediated clearance. Even worse, trans fats raise LDL and lower HDL. To learn more about the different fats, see "Unsaturated Fats", "Saturated Fats", and "Trans Fats".
LDL is a low-density lipoprotein ("bad cholesterol") that carries cholesterol from the liver to the rest of the body through the bloodstream. Cells bind to LDL in order to extract necessary fat and cholesterol from them for the body's use. However, when the bloodstream carries too much LDL, it can form deposits on the walls of arteries, along with other fatty substances, creating plaque, which can narrow arteries and limit blood flow. When plaque breaks apart, it can clog arteries and cause a heart attack or stroke.
LDL
HDL
HDL is a high-density lipoprotein ("good cholesterol") that takes cholesterol from the bloodstream, LDL, and artery walls and brings it back to the liver.