Low-Density Lipoproteins (LDL)
After VLDL has lost the triglycerides, the remaining particle is known as low-density lipoproteins (LDL). Both the VLDL and LDL bring triglycerides in the cells. These lipoproteins are now called low-density lipoproteins (LDL). About half of the LDL is made up of cholesterol. The LDL has the greatest amount of cholesterol than any other form of blood lipoprotein. It contains 45% cholesterol, 10% triglycerides, 22% phospholipid and 25% protein. An LDL is made mainly of cholesterol because more of the triglycerides were removed from the original VLDL. It is lower in lipid than the intermediate density lipoprotein (IDL) and therefore even more dense. For a cell to absorb an LDL particle, it needs a receptor on the cell to bind it. This receptor brings the particle inside the cell.
Cells with LDL receptors pick up the LDL particles and bring them inside the cell. They are then broken down, and the cholesterol and protein parts are transported throughout the cell to be used to support cell growth and development.
The progression of heart disease occurs when cholesterol builds up on the blood vessel walls. There can be an injury to the cell wall from cigarette smoking, drugs, alcohol and other things. To heal the injury site, scavenging white blood cells from the circulating blood deposit in the injury site and become buried in the blood vessels. When these cells see the LDL particles floating along in the blood, they grab them up. When blood cholesterol level is higher, it happens faster. The LDL molecule changes due to the oxidation by the scavenger cells, and it will stay buried in the blood vessel. Cholesterol then builds up in these scavenger cells. When a lot of cholesterol and other materials build up in blood vessels over time, this results in a narrowing of the vessel, and the blood vessel becomes hard. It loses its ability to expand and contract as needed. This, in turn, increases a person's blood pressure. High blood pressure is a risk factor for a heart attack or other health problems.
High-Density Lipoproteins (HDL)
There are other kinds of lipoproteins that help remove fat from the body cells and return them to the liver for recycling to use again or to get rid of them. These are known as high-density lipoproteins (HDL). HDL picks up unused cholesterol and returns it to the liver. Both the liver and intestine make small lipoproteins known as high-density lipoproteins (HDL). Fatty acids in the bloodstream are always bound or connected to a protein in blood called albumin while they are moved from storage in the adipose cells to the liver, muscles and other places in the body.
Play it again, Sam:
During digestion most fatty acids must be removed from the triglyceride molecules. Once dietary fat is digested and absorbed into the cells of the small intestine, triglycerides are reformed. They combine with phospholipids and cholesterol and are packaged into a chylomicron, which is a large droplet of fat surrounded by a thin shell of protein, cholesterol and phospholipid. This combination of lipid (fat) and protein is called a lipoprotein. Lipids (fats) cannot dissolve in water or liquid. Think of oil and vinegar and how they can't mix. Since blood is a liquid or watery, fat can't dissolve in it. In order for fat to travel in the bloodstream, the body surrounds a fat droplet with a layer of protein, phospholipid and cholesterol. You might think of a fat molecule similar to a M&M candy, with the fat being the chocolate center or inside and the protein, phospholipid and cholesterol being the hard outer shell of the candy.
Chylomicrons in the blood are acted on by the enzyme called lipoprotein lipase. This enzyme action is needed to get fats inside cells. Lipoprotein lipase breaks down the triglycerides in the chylomicrons into free fatty acids and glycerol. Most of the glycerol travels through the blood to cells in the liver or kidney. There it can be made into glucose. Muscle, fat and other cells in the surrounding area absorb most of the fatty acids. The absorbed fatty acids can immediately be used for energy or reformed into triglycerides.
Role of liver in fat and cholesterol production
We get triglycerides and cholesterol from two sources: from food and also from the liver, with the liver being the major lipid (fat) producing organ in the body. The liver supplies the body with triglycerides and cholesterol. When we eat more calories than we need, some of the proteins and carbohydrates are broken down by the liver. The resulting carbons and hydrogens are used to make triglycerides and cholesterol. The fat that is not needed in the body is then stored in adipose tissue. Liver is the primary organ that produces fat in the body, not adipose tissue. In thinking about the percentage of fat we have, it is important to think about both the recommended amount of fat we need each day and also the recommended number of calories we need. It is important to eat the recommended amount of fat as well as calories each day. Otherwise, the liver may turn the extra proteins, carbohydrates and alcohol, if consumed, into fat.
Cholesterol
Cholesterol is a fatty substance found only in foods that come from animals. Our body gets cholesterol from two sources - our body makes it, and the foods we eat that contain cholesterol. The liver makes about 800 milligrams of cholesterol each day. We eat about 300 to 500 milligrams of cholesterol. Our body produces cholesterol, but we also get it from food that comes from animal sources. Meats, egg yolks and milk products, such as butter and cheese, and organ meats have cholesterol. We make cholesterol whether we eat it or not. When our diets are very low in cholesterol, we make more.
Cholesterol has an important role in our body. It is a part of cell membranes. It is an essential part of each cell. Also, the liver uses cholesterol to make bile acids, which aid digestion. The body also uses cholesterol to produce certain hormones. Although it is important for us to get some cholesterol, too high of cholesterol levels in our blood increase the risk of heart disease.
Blood Levels of Cholesterol and Triglycerides
Cholesterol and triglycerides are two of the major fatty substances in the blood. Triglycerides may be used by cells for energy or they may be stored to use later. Doctors measure the amount of cholesterol and triglycerides in blood to help determine a person's health. High levels of triglycerides, especially if accompanied by high levels of cholesterol, increase the risk of heart disease. They also are often associated with obesity, diabetes, hypertension, low HDL and small, dense LDL particles. Thus, an increased triglycerides level may be a marker for the presence of other metabolic disturbances. Weight loss, increased physical activity and moderation of alcohol consumption are often effective for reducing the triglycerides level. Eating one to two fish meals per week markedly decreased triglycerides levels by about 20% to 52%.
Blood Cholesterol
Total blood cholesterol is made of three different parts:
- Low-density lipoprotein cholesterol or LDL-C (the bad one).
- Very-low-density lipoprotein cholesterol or VLDL-C.
- High-density lipoprotein cholesterol or HDL-C (the good or heart-healthy one).
Not only do you need to be concerned with your total blood cholesterol level, but you also need to be concerned with the good or HDL-C level as well. The good or heart-healthy component is HDL-C. This level needs to be high.
The LDL-C is the one that is dangerous. It is associated with the development of atherosclerosis. This level needs to be low.
Desirable total blood cholesterol is less than 200 mg/dL. This is the heart-healthy level.
Borderline-high total cholesterol is 200-230 mg/dl.
High total blood cholesterol is 240 or greater.
HDL-C
An elevated or high HDL-C of 60 mg/dL or more is heart healthy. An HDL-C of less than 35mg/dL is low. The HDL level needs to be high to be heart healthy.
LDL-C
Elevation of LDL-C is the most common cholesterol component to become abnormal. Since this is the heart unhealthy one, we need to especially be concerned about our LDL-C level. LDL-C level needs to be lowered from 190 or above to 130. A new study suggests that people with an LDL-C of just 150 might benefit from lowering that number to 115.
Lower LDL-C, the bad one, by limiting total fat intake to 30% or less of total calories and lose weight, if needed. Certain water-soluble dietary fibers that become thick or viscous lower LDL-C and total cholesterol when eaten in sufficient amounts. Changes that occur in the total cholesterol result from lowering the LDL component of cholesterol. Sources of water-soluble fiber include psyllium husk, beta-glucan from oat and barley products, guar gum and pectin. Adding six grams per day to 12 grams per day of soluble fiber to a heart-healthy diet produces additional LDL-C reductions of 5% to 15%.
VLDL-C
Seafood oils high in the omega-3 fatty acids lower blood levels of VLDL-C. Studies show that seafood oils help protect people from heart disease. People who eat seafood oils have fewer deaths from cardiovascular disease than those who don't.
Sardines in sardine oil are very rich in the omega-3 fatty acids. Other sources include mackerel, salmon, trout, tuna, soybean oil, margarine with soybean oil, and black walnuts.
Fatty acids in seafood oils help promote heart health by helping the heart maintain a regular heartbeat and not getting out of rhythm (cardiac arrhythmia). Cardiac arrhythmias are thought to cause many sudden cardiac deaths. Eating at least one fish meal per week by people who are high-risk may help protect them from developing a dangerous irregular heart beat.
Low High-Density Lipoprotein Cholesterol - the good or heart-healthy one
For high-density lipoprotein cholesterol to be considered low, it needs to be a concentration less than 35 mg/dL. A value of 60 mg/dL or more is considered to be heart healthy.
What lifestyle factors lower the heart-healthy HDL?
- Cigarette smoking
- Obesity
- Postmenopausal status ·
What is a lifestyle factor that raises the heart-healthy HDL?
What can you do if you have a low heart-healthy HDL level?
Take estrogen replacement therapy upon your doctor's orders, if you are postmenopausal.