Cholesterol, also called blood cholesterol, is a natural waxy sub- stance that occurs in all your body cells. It is one of several types
of fats (lipids) that circulate in your bloodstream. Your body uses it to form cell membranes and to make certain hormones, and therefore at healthy levels it is an essential component of cells and blood. Your liver makes as much cholesterol as your body needs—about 1,000 milligrams (mg) per day.
You consume cholesterol (dietary cholesterol) in the foods you eat, especially animal products such as meats, eggs, and dairy foods. If cho- lesterol levels are high, cholesterol can be deposited in the blood vessel walls as a major component of plaque (a fatty deposit). A buildup of plaque restricts the blood ?ow, a process called atherosclerosis, and puts you at greatly increased risk of heart disease.
Triglycerides are the true blood fat that exists in the body as well as in food. Triglycerides circulate in your blood along with cholesterol and are fuel for your body’s energy production. Together, cholesterol and triglycerides in the blood are called plasma lipids. Excess calories that you consume in foods are converted to triglycerides and are carried to fat cells for storage. In between meals, hormones control the release of triglycerides to meet your body’s need for energy. Like cholesterol, triglycerides can build up in the blood and contribute to atherosclerosis.

Because neither cholesterol nor triglycerides can dissolve in the blood, they have to be moved to and from cells by carriers called lipoproteins. The two most common types, the ones you hear the most about, are low-density lipoproteins (LDL), the “bad cholesterol,” and high-density lipoproteins (HDL), the “good cholesterol.” LDLs have a lower density of protein (about 25 percent) and more cholesterol. HDLs have a higher density of protein (about 50 percent) and less cholesterol.
If too much LDL accumulates in your blood, it causes fatty plaque to collect on your arterial walls, and the process of atherosclerosis begins. If the buildup reduces blood ?ow in the arteries that supply your heart, you may experience the chest pains known as angina. If a blood clot forms near the plaque and stops the blood ?ow, you have a heart attack. If a clot blocks blood ?ow to your brain, you have a stroke. Your LDL levels increase when you consume foods that contain lots of fat, choles- terol, or both. Foods rich in saturated fats and trans fats, such as butter fat, cheese, red meat, processed meats, and bakery goods, are the most harmful, along with tropical oils found in some products like crackers (see also pages 27–29).
High-density lipoproteins carry cholesterol back from your cells to your liver, where it can be passed out of the body. Most doctors think that HDL can actually slow down the development of plaque by remov- ing cholesterol from it. A high level of HDL seems to protect against heart attack, and a low level places you at greater risk of heart attack and stroke.

Cholesterol transport
5Your liver produces blood cholesterol, a waxy substance that your body uses to build cells and make hormones, and you consume additional cholesterol in foods. Cholesterol is trans- ported to cells through the bloodstream on carrier particles called lipoproteins. Low-density lipoprotein (LDL) consists of
less protein and more cholesterol, and it can be harmful at high levels when it builds up on the walls of your arteries as plaque. Very low-density lipoprotein (VLDL) is another form of choles- terol that can convert to LDL and cause problems. High-density lipoprotein (HDL; shown as smaller units), which consists of more protein and less cholesterol, can absorb some of the cho- lesterol in plaque and return it to the liver to be excreted. So you need to try to reach a high enough level for HDL in your bloodstream to help protect against heart attack and stroke.