Cholesterol is a chemical compound that is naturally produced by the body and is a combination of lipid (fat) and steroid. LDL cholesterol is also called "bad" cholesterol, because it is associated with an increased risk of coronary heart disease. LDL deposits on the artery walls, causing the formation of a hard, thick substance called cholesterol plaque. Over time, cholesterol plaque causes thickening of the artery walls and narrowing of the arteries. Diets that are high in saturated fats and cholesterol raise the levels of LDL cholesterol in the blood.