If your health professional says you have hyperlipidemia, this simply means the amount of fat in your blood is higher than it should be. ("Hyper" means high; "lipid" is another word for fat or fat-like substance; "emia" refers to the blood.) Although high cholesterol is the most famous form of hyperlipidemia, blood fats include more than just cholesterol. Triglycerides, phospholipids, and other fatty substances circulate continuously through the bloodstream on their way to and from organs and tissues.

High blood cholesterol gets the most attention because of the link between cholesterol and heart disease. Cholesterol has received a great deal of press, and medical experts agree that high blood cholesterol is a risk factor for heart disease. But cholesterol is not an enemy. The body needs cholesterol and manufactures its own supply. Essential for life, cholesterol plays many important roles. Cholesterol, along with other fats, is a key component of cells membranes. The body uses cholesterol as the building material for hormones such as estrogen and testosterone. Bile salts, which break the fat we eat into small particles that can be digested, are composed largely of cholesterol. Cholesterol is our friend, something the body requires, in the right places and amounts.

Abnormally high levels of cholesterol in the blood can lead to coronary heart disease and other serious conditions, due to build-up of cholesterol-filled plaque in the arteries. But cholesterol by itself is not the problem. Research has shown that abnormalities in the way cholesterol is transported in the blood are the culprits in setting the stage for arteries to become damaged and clogged with plaque. (This is the condition known as "atherosclerosis.")

Blood is a watery fluid. Since oil and water do not mix, fats do not travel in the blood in their free form. Instead, they are bundled together with other substances for transport through the blood vessels and delivery to destinations where they are needed in the body. Cholesterol and other fats are shipped in the form of fat-protein packages called "lipoproteins." Four groups of lipoproteins use the bloodstream as an aqueduct: LDL, VLDL, HDL, and chylomicrons. The protein portion of a lipoprotein forms a sort of shell around the fat and also directs the lipoprotein to its appointed delivery site in tissues and organs.

Chylomicrons, a major transport container for triglycerides, are large particles that carry digested fat from the intestines to the liver. (Fats are broken down into fatty acids in the digestive tract, and then packaged together in groups of three. A triglyceride contains three fatty acids attached to glycerol.) Rich in triglycerides, chylomicrons also ferry cholesterol absorbed from food to the liver. Fat-digesting enzymes break down chylomicrons fairly quickly, so most are gone from the blood after a 12 to 14 hour fast.

VLDL, or "very low-density lipoproteins" also transport triglycerides and cholesterol. Formed in the liver and intestines, VLDL carry about 10 to 15 percent of the cholesterol found in blood. VLDL delivers cholesterol and triglycerides to cells, which in turn put these lipid products to use.

Through the action of fat-digesting enzymes, VLDL becomes progressively smaller as it circulates through the bloodstream. Remnants of VLDL can contribute to plaque-formation in the arteries. VLDL also converts to LDL, which is the chief culprit in atherosclerosis.

LDL, or "low-density lipoprotein," is the blood lipid that cause the most concern. Compared to other lipoproteins, LDL has a much greater tendency to deposit cholesterol in the walls of blood vessels. Because LDL is the most plaque-forming form of cholesterol, the likelihood of developing atherosclerosis is directly related to the concentration of LDL in the blood. Lowering LDL is the primary goal in treating hyperlipidemia.

HDL, or<