Cholesterol is a lipidic, waxy steroid found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and fluidity. Cholesterol is the principal sterol synthesized by animals, but small quantities are synthesized in other eukaryotes, such as plants and fungi. It is almost completely absent among prokaryotes, which include bacteria. Cholesterol is classified as a sterol (a portmanteau of steroid and alcohol).
Total fat intake, especially saturated fat and trans fat, plays a larger role in blood cholesterol than intake of cholesterol itself. Saturated fat is present in full fat dairy products, animal fats, several types of oil and chocolate. Trans fats are derived from the partial hydrogenation of unsaturated fats, and in contrast to other types of fat, they are not essential for life. It is recommended that trans fats be consumed extremely rarely or not at all as they are said to be more harmful than naturally occurring oils. Trans fat can be found in the commercial food supply including fast food, snack foods, fried food and baked goods.
A change in diet may help reduce blood cholesterol in addition to other lifestyle modifications. Avoiding animal products may decrease the cholesterol levels in the body not through dietary cholesterol reduction alone, but primarily through a reduced saturated fat intake. Those wishing to reduce their cholesterol through a change in diet should aim to consume less than 7% of their daily calories from saturated fat and less than 200 mg of cholesterol per day.
The view that a change in diet (specifically, a reduction in dietary fat and cholesterol) can lower blood cholesterol levels, and thus reduce the likelihood of development of, amongst others, coronary artery disease (CHD) has been challenged. An alternative view is that any reductions to dietary cholesterol intake are counteracted by the organs such as the liver, which will increase or decrease production of cholesterol to keep blood cholesterol levels constant.
It is recommended by the American Heart Association to test cholesterol every 5 years for people aged 20 years or older.
A blood sample taken after fasting is taken by a doctor or a home cholesterol monitoring device to determine a lipoprotein profile. This measures total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol and triglycerides. It is recommended to have cholesterol tested more frequently than 5 years if a person: has total cholesterol of 200 mg/dL or more, if a man over age 45 or a woman over age 50, has HDL (good) cholesterol less than 40 mg/dL, or other risk factors for heart disease and stroke.
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