The Healthy Diet »

Cholesterol is a waxy white substance that humans and animals make from fat. Plants do not make cholesterol and therefore no cholesterol is present in vegetarian foods. All meat, poultry, shellfish, dairy prod­ucts and egg yolks contain cholesterol.

In your body, cholesterol helps form the outer membrane of cells and provide an insulated sheath around nerve fibers. Although cholesterol is needed throughout the body, you do not have to eat foods containing cholesterol in order to be healthy. Your liver can easily produce all the cholesterol your body needs if you consume the recommended amount of fat (no more than 30 percent of your daily calories). Besides its normal healthy functions, cholesterol can also form de­posits on blood vessel walls — a condition known as arteriosclerosis, which, in its advanced stages, is the most common cause of heart disease. When these deposits build up so that they severely limit blood flow through an artery or cut off the flow entirely, the result can be a fatal heart attack or stroke.

Numerous studies have shown that diets high in saturated fat and cholesterol result in high levels of cholesterol in the bloodstream, while diets that contain a great deal of unsaturated fat tend to reduce blood cholesterol. Medical researchers have also identified cholesterol carriers in the blood that can more accurately reveal the condition of the cardiovascular system. Known as lipoproteins, these substances transport cholesterol through the bloodstream. There are two main types of lipoproteins: high-density lipoproteins, or HDL's, and low-density lipoproteins, or LDL's. By mechanisms that researchers do not entirely understand, LDL's deliver cholesterol to the body's cells, and in the process deposit some of it on the arterial walls; HDL's, however, appear to take cholesterol out of the bloodstream to the liver, where it can be broken down and eliminated. So although a person's overall cholesterol level is important as an indication of cardiovascular health, studies have established that a high le el of LDL's is particularly associated with coronary heart disease.

Research indicates that diets high in unsaturated fat lower not only total blood cholesterol, compared to diets containing large amounts of saturated fat, but they also lower the level of harmful LDL's. (Diet appears to have little effect on HDL levels.) For instance, studies Cholesterol and Heart Disease comparing Japanese and American diets show that the Japanese, who consume very little saturated fat, have much lower levels of total cholesterol and LDL's than Americans, whose diet is high in saturated fat. And Japanese who move to North America and switch to a typical high-fat American diet experience a rise in blood cholesterol.