Lipids: Cholesterol and Triglyceride
The fat and fat-like substances in the blood are called lipids and include both cholesterol and triglycerides. Cholesterol is present in every cell of your body. It is used to form cell membranes and part of some hormones. The body manufactures the majority of required cholesterol, mostly in the liver; therefore, excessive dietary cholesterol intake is unnecessary and may be harmful.
Animal foods such as meats, poultry, fish, seafood, egg yolks, and dairy products are rich in cholesterol. Plant foods such as fruits, nuts, seeds, vegetables and grains do not contain cholesterol.
Cholesterol will not dissolve in the bloodstream; it is transported to and from cells by special carriers called lipoproteins. The low density lipoprotein (LDL) is the major cholesterol carrier in the blood and contributes to plaque formation in the arteries. When clots form at the site of plaques, blood flow is interrupted, leading to heart attacks or strokes. Thus LDL cholesterol is known as the bad cholesterol.
The high density lipoprotein (HDL) is mostly made by the liver. It is thought to carry cholesterol away from the arteries and away from plaques back to the liver where it is eliminated. Thus high levels of HDL cholesterol are good; likewise, low levels increase the risk of heart attacks. HDL levels are difficult to raise.