"Eat a low-fat, low-cholesterol diet." Most of us have heard this simple recommendation so often over the past two decades that we can recite it in our sleep. Touted as a way to lose weight and prevent cancer and heart disease, it's no wonder much of the nation - and food producers - hopped on board.

Unfortunately, this simple message is now largely out of date. Detailed research -much of it done at Harvard - shows that the total amount of fat in the diet, whether high or low, isn't really linked with disease. What really matters is the type of fat in the diet. New results from the large and long Women's Health Initiative Dietary Modification Trial showed that eating a low-fat diet for 8 years did not prevent heart disease, breast cancer, or colon cancer, and didn't do much for weight loss, either.

What is becoming clearer and clearer is that bad fats, meaning saturated and trans fats, increase the risk for certain diseases while good fats, meaning monounsaturated and polyunsaturated fats, lower the risk. The key is to substitute good fats for bad fats.

And cholesterol in food? Although it is still important to limit the amount of cholesterol you eat, especially if you have diabetes, dietary cholesterol isn't nearly the villain it's been portrayed to be. Cholesterol in the bloodstream is what's most important. High blood cholesterol levels greatly increase the risk for heart disease. But the average person makes about 75% of blood cholesterol in his or her liver, while only about 25% is absorbed from food. The biggest influence on blood cholesterol level is the mix of fats in the diet.

Cholesterol is a wax-like substance. The liver makes it and links it to carrier proteins called lipoproteins that let it dissolve in blood and be transported to all parts of the body. Why? Cholesterol plays essential roles in the formation of cell membranes, some hormones, and vitamin D.

Too much cholesterol in the blood, though, can lead to problems. In the 1960s and 70s, scientists established a link between high blood cholesterol levels and heart disease. Deposits of cholesterol can build up inside arteries. These deposits, called plaque, can narrow an artery enough to slow or block blood flow. This narrowing process, called atherosclerosis, commonly occurs in arteries that nourish the heart (the coronary arteries). When one or more sections of heart muscle fail to get enough blood, and thus the oxygen and nutrients they need, the result may be the chest pain known as angina. In addition, plaque can rupture, causing blood clots that may lead to heart attack, stroke, or sudden death. Fortunately, the buildup of cholesterol can be slowed, stopped, and even reversed.

Cholesterol-carrying lipoproteins play central roles in the development of atherosclerotic plaque and cardiovascular disease. The two main types of lipoproteins basically work in opposite directions.

Low-density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body. When there is too much LDL cholesterol in the blood, it can be deposited on the walls of the coronary arteries. Because of this, LDL cholesterol is often referred to as the "bad" cholesterol.

High-density lipoproteins (HDL) carry cholesterol from the blood back to the liver, which processes the cholesterol for elimination from the body. HDL makes it less likely that excess cholesterol in the blood will be deposited in the coronary arteries, which is why HDL cholesterol is often referred to as the "good" cholesterol.

In general, the higher your LDL and the lower your HDL, the greater your risk for atherosclerosis and heart disease.

Learn more at: http://www.hsph.harvard.edu/nutritionsource/fats.html