Cholesterol is a white, waxy lipid (fat) that is present in the tissues of humans and other animals and, thus, in all foods from animal sources. Although cholesterol is essential for many bodily functions, it isn't an essential nutrient, meaning that the diet does not need to contain cholesterol to meet the body's requirements. The liver manufactures all the cholesterol that the body needs. Particles called lipoproteins, formed in the liver, transport cholesterol and other fats through the bloodstream. The three lipoproteins are named according to their density: very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). Most cholesterol is transported by LDL.
The liver secretes VLDL, which is converted to LDL in the bloodstream. The cholesterol on LDL is used to form membranes in cells throughout the body; deposits of LDL cholesterol in the arterial walls initiate the formation of plaques.
HDL also carries cholesterol in the blood; however, HDL has the beneficial capacity of picking up cholesterol from cells and atherosclerotic plaques and bringing it back to the liver for reprocessing or excretion. Therefore, HDL cholesterol is often referred to as "good" cholesterol, because it clears cholesterol from the arteries, while LDL cholesterol has been called "bad" because it deposits cholesterol in the arteries. Because elevated cholesterol levels contribute to the development of atherosclerosis, reducing cholesterol levels can help prevent coronary heart disease and heart attacks.
