Dietary cholesterol - Definition, Description, Functions, Benefits, Precautions, Risks

Definition :

Cholesterol is a soft, white, waxy substance found in the lipids of the bloodstream and in the cells of the body. There are two sources of cholesterol. The first is the body, mainly the liver, which produces typically about 1g per day. The second are cholesterol-containing foods from animal sources, especially egg yolks, meat, poultry, fish, seafood and whole-milk dairy products. This is the cholesterol called dietary cholesterol, because it is obtained from the diet.

Purpose :

Cholesterol is found in every cell of the body and it has several important functions in maintaining health such as:

•  keeping cell membranes intact
•  boosting mental performance
•  helping digestion
•  building strong bones
•  building muscle
•  maintaining energy, vitality, and fertility
•  regulating blood sugar levels
•  repairing damaged tissue
•  protecting against infectious diseases

However, excess cholesterol has been shown to accumulate in the bloodstream and on the walls of arteries, forming ‘‘plaques’’ that can clog the blood vessels (atherosclerosis) and lead to heart attacks and strokes. Because high blood cholesterol is one of the major risk factors for heart disease, dietary cholesterol has been the focus of much debate over what represents healthy or unhealthy levels of cholesterol in the blood and how to lower cholesterol in the diet.

Description :

Dietary cholesterol is found in animal food sources such as meat, poultry, seafood and dairy products. Foods from plants, such as fruits, vegetables, vegetable oils, grains, cereals, nuts and seeds, do not contain cholesterol. Major sources of dietary cholesterol include:

•  beef liver, 3 ounces cooked (331mg)
•  beef sweetbreads, 3 ounces cooked (250mg)
•  squid, 3 ounces cooked (227mg)
•  egg, whole, large (212mg)
•  shrimp, 3 ounces cooked (166mg)
•  scallops, 3 ounces cooked (27mg)
•  milk, whole, 1 cup (33mg)
•  cheese, regular cheddar, 1 ounce (30mg)
•  cheese, reduced fat, 1 ounce (6mg)
•  ice cream, gourmet, 1 cup (90mg)
•  ice cream, light, 1 cup (31mg)
•  beef, sirloin, 3 ounces cooked (71mg)
•  beef, round, 3 ounces cooked (71mg)
•  beef, rib eye, 3 ounces cooked (65mg)
•  pork chop, 3 ounces cooked (71mg)
•  ham, regular, 3 ounces cooked (50mg)
•  lamb chop, 3 ounces cooked (75mg)
•  chicken breast, 3 ounces cooked (72mg)
•  chicken, dark, 3 ounces cooked (70mg)

Cholesterol does not dissolve in blood. It has to be transported to and from the cells by special carriers called lipoproteins. These are present in blood plasma and the most important are:

•  Very high-density lipoprotein (VHDL). VHDL consists of proteins and a high concentration of free fatty acids.
•  High-density lipoprotein (HDL). HDL helps remove fat from the body by binding with it in the bloodstream and carrying it back to the liver for excretion in the bile and disposal. A high level of HDL may lower chances of developing heart disease or stroke.
•  Intermediate-density lipoprotein (IDL). IDLs are formed during the degradation of very-low-density lipoproteins; some are cleared rapidly into the liver and some are broken down to low-density lipoproteins.
•  Low-density lipoproteins (LDL). LDL transports cholesterol from the liver and small intestine to tissues outside the liver (extrahepatic) and other parts of the body. A high LDL level may increase chances of developing heart disease.
•  Very low-density lipoprotein (VLDL). VLDLs carry triglycerides from the intestine and liver to fatty (adipose) and muscle tissues; they contain primarily triglycerides. A high VLDL level can cause the buildup of cholesterol in arteries and increase the risk of heart disease and stroke.
•  Chylomicrons. Proteins that transport cholesterol and triglycerides from the small intestine to tissues after meals.

Generally speaking, LDL levels should be low, because LDL deposits cholesterol in the arteries and causes them to become clogged, and HDL levels should be high, because HDL helps clean fat and cholesterol from arteries, carrying it to the liver for removal from the body. This is why HDL is often called the ‘‘good cholesterol’’ and LDL the ‘‘bad cholesterol’’.

Precautions :

The National Heart, Lung and Blood Institute (NHLBI), through its National Cholesterol Education Program (NCEP), recommends that adults begin cholesterol screening at age 20 and repeat the screening every five years. Persons who have one or more risk factors for developing heart disease (for example diabetes, kidney disease, high blood pressure, vascular disease, a history of elevated cholesterol levels) should have their cholesterol levels checked more often.

Simple blood tests are done to check blood cholesterol levels. A lipoprotein test, also called a fasting lipid test, is commonly performed as part of a routine medical examination. A cholesterol test measures lipid levels and usually reports on four groups:

•  Total cholesterol (normal: 100–199 mg/dL)
•  LDL (normal: less than 100 mg/dL)
•  HDL (normal: 40–59 mg/dL)
•  Triglycerides (normal: less than 150 mg/dL)

Interactions :

Dietary fats are known to interact with cholesterol as follows:

•  monounsaturated fats (olives, olive oil, canola oil, nuts, avocados) lower LDL, raise HDL
•  polyunsaturated fats (corn, soybean, safflower, cottonseed oils, fish) lower LDL, raise HDL;
•  saturated fats (whole milk, butter, cheese, ice cream, red meat; chocolate, coconuts) raise both LDL and HDL;
•  trans fats (most margarines, vegetable shortening, partially hydrogenated vegetable oil, deep- fried chips, many fast foods, most commercial baked goods) raise LDL

Aftercare :

The American Heart Association (AHA) endorses the following dietary recommendations for people with high blood cholesterol:

•  total fat: 25% of total calories
•  saturated fat: less than 7% total calories
•  polyunsaturated fat: up to 10% total calories
•  monounsaturated fat: up to 20% total calories
•  carbohydrates: 50–60% total calories
•  protein: about 15% total calories
•  cholesterol: less than 200 mg/dL
•  plant sterols: 2g
•  soluble fiber such as psyllium: 10– 25g

Categories of appropriate foods include:

•  lean meat/fish: less than 5oz/day
•  eggs: less than 2 yolks per week (whites unlimited)
•  low-fat dairy products (<1% fat): 2–3 servings/day
•  grains, especially whole grains: 6–8 tsp/day
•  vegetables: less than 6 servings per day
•  fruits: 2–5 servings per day

Complications :

If dietary cholesterol intake is excessive, it can lead to an elevation of lipid levels in the bloodstream (hyperlipidemia). These lipids include cholesterol, phospholipids and triglycerides (fats). Hypercholesterolemia is the term for high cholesterol levels, and hypertriglyceridemia is the term for high triglyceride levels. Because cholesterol-rich foods are also usually high in saturated fat, hypercholesterolemia is often combined to hypertriglyceridemia. Hyperlipidemias have been shown to represent a major risk factor for heart disease, the leading cause of death in the United States.

Parental concerns :

Parents can make dietary choices that can prevent cholesterol levels from being too high. For instance, they can follow these guidelines:

•  Select only the leanest meats, poultry, fish and shellfish. Choose chicken and turkey without skin or remove skin before eating. Some fish, like cod, have less saturated fat than either chicken or meat.
•  Limit goose and duck. They are high in saturated fat, even with the skin removed.
•  Some chicken and turkey hot dogs are lower in saturated fat and total fat than pork and beef hot dogs. There are also lean beef hot dogs and vegetarian sausages that are low in fat and saturated fat.
•  Dry peas, beans and tofu can be used instead of meat because they are low in saturated fat and cholesterol. Dry peas and beans also have a lot of fiber, which can help to lower blood cholesterol.
•  Egg yolks are high in dietary cholesterol. A yolk contains about 213 mg. They should be limited to no more than 2 per week, including the egg yolks in baked goods and processed foods. Egg whites have no cholesterol, and can be substituted for whole eggs when baking.
•  Regular dairy foods that contain fat, such as whole milk, cheese, and ice cream, are also high in saturated fat and cholesterol. But dairy products are an important source of important nutrients such as calcium and the diet should include 2 to 3 servings per day of low- fat or nonfat dairy products.
•  When shopping for hard cheeses, select them fat-free, reduced fat, or part skim.
•  Select frozen desserts that are lower in saturated fat, such as ice milk, low- fat frozen yogurt, low-fat frozen dairy desserts, sorbets, and popsicles.
•  Saturated fats should be replaced with unsaturated fats. Select liquid vegetable oils that are high in unsaturated fats, such as canola, corn, olive, peanut, safflower, sesame, soybean, and sunflower oils.
•  Limit butter, lard, and solid shortenings. They are high in saturated fat and cholesterol.
•  Select light or nonfat mayonnaise and salad dressings.
•  Fruits and vegetables are very low in saturated fat and total fat, and have no cholesterol. Fruits and vegetables should be eaten as snacks, desserts, salads, side dishes, and main dishes.
•  Breads, cereals, rice, pasta, grains, dry beans, and peas are high in starch and fiber and low in saturated fat and calories. They also have no dietary cholesterol, except for some bakery breads and sweet bread products made with high fat, high cholesterol milk, butter and eggs.
•  Select whole grain breads and rolls whenever possible. They have more fiber than white breads.
•  Most dry cereals are low in fat. Limit high-fat granola, and cereal products made with coconut oil and nuts, which increases the saturated fat content.
•  Restrict sweet baked goods that are made with saturated fat from butter, eggs, and whole milk such as croissants, pastries, muffins, biscuits, butter rolls, and doughnuts.
•  Snacks such as cheese crackers, and some chips are often high in saturated fat and cholesterol. They can be replaced by low-fat snacks such as bagels, bread sticks, cereals without sugar, frozen grapes or banana slices, dried fruit, non-oil baked tortilla chips, popcorn or pretzels.