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It's Your Heart -- Keep It Ticking
YOU GO TO THE DOCTOR for a physical. You're feeling great. You're not too heavy -- well, just a few pounds; a bit soft and blubbery around the middle. But you've never felt better. You get a little breathless walking up steps, but other than that, you feel like a twenty-year old. Your doctor sits you down. His expression is serious. "You are in good physical condition," he tells you, "but your blood cholesterol is 245." "So" you ask. "So," he answers, "you're a good candidate for a heart attack. The higher your blood cholesterol, the higher your risk of heart disease."
You feel a queasy sensation in your stomach. Your head begins to spin. "What is blood cholesterol' you ask. "How does it affect my heart? You've read about cholesterol in the newspapers. You remember something about HDL, or good cholesterol, and triglycerides, but it never really sank in. Now you're ready to listen. You need to understand it. It's your heart. It's your life.
THE HEART AND HEART DISEASE
The heart is a muscle that pumps blood throughout the body to deliver nutrients to all the body's cells and to remove waste materials. Just how much work the heart does is mind-boggling. Even while you rest or sleep, the heart beats between 70 and 80 times each minute and pumps nearly 5 quarts of blood. That adds up to about 100,000 beats and about 1800 gallons of blood pumped each day.
During vigorous exercise, the heart can increase its output nearly fivefold. Blood is kept moving through the extensive network of arteries, capillaries, and veins by the pumping heart at such a rate that blood can make the trip from the heart to the big toe and back in less than one minute.
In order to do all this work, the heart muscle needs a constant supply of nutrient-rich, oxygenated blood. This is supplied by the coronary arteries that branch off from the aorta (see Figure 2*).
What Is Atherosclerosis? The underlying cause of coronary heart disease is a process called atherosclerosis. Atherosclerosis is the clogging of the coronary arteries with fatty, fibrous, cholesterol-laden deposits (called atheromata or plaques). These deposits thicken the artery wall, thus narrowing the channel through which the blood flows. Plaques are caused by an excess of cholesterol in the blood (see Figure 3*).
When Does Atherosclerosis Begin? In countries where people eat foods high in saturated fat, plaque begins to develop in childhood (see page 152). Plaque formation progresses at different rates in different people, depending on their ability to metabolize fat. (Both high blood pressure and smoking speed up the rate of atherosclerosis.) Over the course of the first three to four decades of life, plaque deposits gradually increase and the openings of the coronary arteries gradually narrow (see Figure 4*).
During this time there are usually no symptoms. You feel good. You are active, in your prime, enjoying the good life. Then suddenly, or so it seems, the inevitable occurs. An artery that feeds blood to the heart muscle becomes 75 percent or more blocked with plaque.
What Is Angina? If you are lucky, the first symptom of coronary heart disease may be angina pectoris. This mildest and earliest symptom is brief chest pain, usually experienced upon exertion. Angina occurs because not enough blood can get through the blocked arteries to supply oxygen to the heart muscle cells. Cells deprived of oxygen for only a few minutes can recover if you rest, thereby reducing the demand on the heart. If the oxygen supply is cut off for longer periods, permanent damage to the heart may result.
The First Symptom May Be Your Last. If you are not so lucky, a small blood clot may become lodged in the narrowed artery and completely block the flow of blood to part of the heart. This part of the heart muscle dies. Result: heart attack or sudden death (see Figure 5*).
WHAT IS CHOLESTEROL AND WHY DO WE HAVE IT?
Let's backtrack. The doctor says your blood cholesterol is too high. What does heart disease have to do with cholesterol?
Cholesterol is an odorless, white, powdery substance (see Figure 6*). It is like a fat in that it does not mix with water. We are concerned with cholesterol because in excess it forms plaque, which clogs the coronary arteries and causes heart disease.
Cholesterol also has many beneficial and vital functions. It is a necessary ingredient of the cell walls of all animals, including humans. Cholesterol in the cell wall helps make your skin waterproof and also slows down water loss by evaporation from the body. Cholesterol is also used in the formation of the steroid and sex hormones. Cholesterol acts as an insulator in the myelin sheath that surrounds nerves and allows normal transmission of nerve impulses.
Cholesterol is transported in the blood stream together with fats. It is in this capacity that cholesterol becomes implicated in heart disease.
In your blood right now are various kinds of particles carrying fat around to do useful work or get stored for later use. Everyone has his or her own balance of the various kinds of particles, depending on diet, heredity, and physical activity. Because we now know one kind of particle is good and another bad, it is worth knowing which is which.Lipoproteins
Fats in your body (and in foods) generally occur as triglycerides. They are transported in blood, which consists mainly of water. They are broken down and their energy released by enzymes, which function in a water medium. However, fats do not mix with water. So fats are packaged into particles to keep them from separating out from the water in the blood. These particles, which also contain proteins and cholesterol, are called lipoproteins (lipo means fat). Four of the major types of lipoproteins are very low density lipoproteins (VLDL), low density lipoproteins (LDL), high density lipoproteins (HDL), and chylomicrons.
VLDL Lipoproteins. The liver uses excess carbohydrates and fats from the foods you eat to make triglycerides (fats). These triglycerides are packaged into VLDL (very low density lipoprotein) particles for distribution from the liver to the rest of the body. VLDL particles contain large amounts of triglycerides and lesser amounts of cholesterol, protein, and other fats. VLDL particles are produced and released into the blood stream in large quantities after meals.
LDL Lipoproteins: The Bad Cholesterol. As the VLDL particles circulate through the blood stream, triglycerides are removed from the particles and enter cells, where they are used as a source of energy. The fat-depleted VLDL particles are called LDL (low density lipoprotein) particles. The cholesterol and protein that remain constitute a large part of the LDL particles.
LDL particles remain in the blood stream for different periods of time in different people. The longer the LDL particles remain in the blood stream, the greater the chance they will become oxidized and taken up by cells called monocytes. Monocytes that have become engorged with LDL-cholesterol lodge in the coronary artery wall. As more and more LDL is oxidized, taken up by monocytes, and lodged in the artery walls, the artery channel becomes more and more narrow. You know the result. When blood can no longer flow through a coronary artery, the part of the heart supplied by that artery dies. Result: heart attack.
Thus, the higher the LDL level in the blood, the more cholesterol is available to clog the coronary arteries and the higher is the risk of developing atherosclerosis and coronary heart disease. The cholesterol in LDL deserves its name of "bad cholesterol." In some people, LDL particles are quickly removed from the blood stream by special LDL receptors on cell surfaces. Once inside the cells, cholesterol from the LDL particles is broken down. When these fortunate people with a normal or high number of LDL receptors have their blood cholesterol measured, their LDL is very low.
Other people have reduced numbers of fully functioning LDL receptors (the genetic constitution and diet of the individual determines the number and activity of the LDL receptors). In these people, LDL particles remain in the blood stream longer, producing a higher LDL level in the blood. Since LDL particles are so rich in cholesterol, a high LDL level results in a high blood cholesterol level.
HDL Lipoproteins: The Good Cholesterol. HDL (high density lipoprotein) particles are the smallest of the lipoprotein particles. HDL removes cholesterol from LDL particles and cells and transports it to the liver. Here most of the cholesterol is broken down into bile acids and excreted into the small intestine. Some of the cholesterol is reprocessed into new VLDL particles.
By removing cholesterol from LDL, HDL prevents cholesterol from accumulating in the coronary arteries and thus protects against the development of heart disease. The higher the HDL level, the more cholesterol is removed from the blood stream and the lower is the risk of heart attack. The lower the HDL level, the less cholesterol is removed from the blood stream, and the greater is the risk of heart disease.
Cholesterol. While cholesterol is not a lipoprotein, it is contained in all the lipoproteins. It is of particular interest because it is a major culprit in the formation of plaque. Cholesterol in the blood is derived partly from cholesterol in the foods you eat and partly from cholesterol made in the liver and the intestine. Because cholesterol is so vital to the normal functioning of the body, all of the body's cholesterol needs can be met by cholesterol made in the liver. In addition, each cell in the body can make cholesterol. Even if you consumed no cholesterol at all (i.e, if you were a strict vegetarian), your body would manufacture enough cholesterol for proper growth and development. However, consumption of too much cholesterol can overload your system and end up as plaque in your coronary arteries.
Note: Cholesterol in foods is not the only, or even the most important, nutrient that affects your blood cholesterol level. The amount of saturated fat in foods is a more important factor in raising blood cholesterol levels, as we will see in Chapter 5.
What Your Cholesterol and Lipoprotein Values Mean
All this talk about lipoproteins and cholesterol is very abstract. You want to know about your lipoproteins and your cholesterol. What do the numbers that you receive from your doctor or from a blood cholesterol screening mean' Do your levels put you at increased risk for heart disease!
First, the total blood cholesterol reading is the sum of the cholesterol in your VLDL, LDL, and HDL particles. Thus, if your total blood cholesterol level is 250, the breakdown may look like this: 45 mg/dL of HDL-cholesterol + 20 mg/dL of VLDL-cholesterol + 185 mg/dL of LDL-cholesterol = 250 mg/dL of total cholesterol.
HDL. Average HDL-cholesterol levels for adult males are about 45 mg/dL and about 55 mg/dL for adult females. Levels lower than average place you at increased risk. The lower they are, the greater your risk. Levels below 35 mg/dL should be a cause for concern. Levels above the average decrease your risk. The higher they are, the lower your risk.
If your HDL is low, you can raise it, but only within narrow limits. Regular aerobic exercise and losing weight if you are overweight will increase your HDL levels. On average, nonsmokers have higher HDL levels than smokers.
A low HDL-cholesterol level coupled with other heart disease risk factors, such as high blood pressure, smoking, or a family history of heart disease, significantly increases risk. You should see your physician and take vigorous steps to reduce these risk factors. You should lower your blood pressure, stop smoking, exercise regularly, and lose weight if you are overweight.
If your HDL-cholesterol is low, you should make a determined effort to lower your LDL-cholesterol. Give your HDL a break. If you eat too much saturated fat, you have an abundance of LDL particles circulating in your blood. To remove the cholesterol from the LDL in your blood, you need a lot of HDL particles. But you don't have a lot of HDL particles. So, the cholesterol in the LDL that the HDL cannot handle remains in the blood and is eventually deposited in your artery walls. However, if you eat less saturated fat, fewer LDL particles circulate in your blood. This gives your HDL a fighting chance. Your HDL particles, although limited in number, are able to remove cholesterol from the smaller amount of LDL particles in your blood so the LDL-cholesterol won't end up clogging your arteries.
Because of their sex hormones, most premenopausal women have higher levels of HDL than do men of the same age. During the thirty or so years that women are protected from developing atherosclerosis by high levels of HDL, many men are accumulating plaque at a fast rate. As a result, many men begin to experience heart disease at early ages (as early as their forties). This is not to imply that women are immune to heart disease. Once women reach menopause and lose their protective hormones, they too begin to develop plaque at a fast rate. Women's risk may rise as much as a thousandfold after menopause. In fact, heart disease is the leading cause of death in women, occurring fifteen to twenty years later than in men.
VLDL and Triglycerides. VLDL is not measured directly. It is calculated from your triglyceride level as follows: VLDL = triglycerides ÷ 5. Triglycerides can be measured only after a twelve-hour fast.
Average values of triglycerides are about 140-150 mg/dL for men and about 100-120 mg/dL for women. Triglycerides are considered a risk factor for heart disease at levels above 150 mg/dL, especially when coupled with an HDL level below 40 mg/dL. If your triglycerides are too high, restrict your intake of simple sugars (sweets) and alcohol (an important factor in raising triglycerides), exercise regularly, and lose weight if you are overweight. Eating less fat and more complex carbohydrates (whole grains, vegetables, and fruits) and regular aerobic exercise will help you lose weight and lower your triglycerides.
LDL. Average levels of LDL-cholesterol are about 135-145 mg/dL for men and about 120-135 mg/dL for women. About half of American adults have levels higher than these. Such levels are too high for long-term health and are the major reason heart disease is the leading cause of death in this country.
You can lower your LDL-cholesterol levels by changing the you eat. Specifically, eating foods low in saturated fats and cholesterol lowers your LDL. Eating less saturated fat increases the number LDL receptors, thus allowing for increased removal of LDL (bad) cholesterol from the blood. Eating less cholesterol reduces the amount of cholesterol available to be made into lipoproteins in the liver and released into the blood.
The majority of total blood cholesterol is carried in the LDL. Since the total blood cholesterol level is a reflection of the LDL level, it is sufficient to monitor only total blood cholesterol. In the rest of is book, we will refer only to total blood cholesterol. But you should now that when you reduce your total blood cholesterol by changing foods you eat, you are primarily lowering your LDL level and thus your risk of heart disease.
Your doctor, health professional, or lab report may have expressed your cholesterol numbers in the form of a ratio. The ratio of total cholesterol to HDL-cholesterol, or the ratio of LDL-cholesterol to HDL-cholesterol, is a shorthand measure of heart disease risk which has been reduced to one number. Ratios take into account the fact that total cholesterol by itself does not tell the full story of your risk. Remember, the higher your LDL level, the higher your risk of coronary heart disease. The higher your HDL level, the lower your risk.
The Two Ratios. Two different ratios are commonly used. Be sure you know which is being used to describe your risk because the actual numerical values of the ratios are quite different.
Ratios as Predictors. With total cholesterol levels between 200 and 240 mg/dL, the ratios are better predictors of your risk than either LDL or total cholesterol alone. However, if your total cholesterol is over 240 mg/dL, LDL alone is the best predictor of risk. Even if your HDL is high, making your ratio look good, it can never be high enough to protect you from such high LDL levels.
Likewise, if your total cholesterol level is very low, your ratio not be a useful predictor of risk. Persons with very low total cholesterol levels, and thus low LDL levels, do not need high HDL levels to protect them. For example, HDL levels are low among rural Japanese, but so are LDL levels. Despite the resulting ratio, heart disease is rare in these people.
YOU CAN CHOOSE TO LOWER YOUR RISKS
Chylomicrons: Yet Another Lipoprotein
If you are sitting there chuckling because you gobble up Quarter Pounders and stuff Wendy's cheese potatoes down your gullet with abandon and still maintain a low total and LDL-cholesterol level, wipe the smile from your lips. New scientific studies show that even with low LDL-cholesterol levels, eating a diet high in fat and saturated fat puts you at risk for heart disease. Eating a low-fat, low-sat-fat diet is still the healthiest route for everyone.
Here's why. In addition to getting fat from the liver, cells get fat directly from the fat in the foods you eat. The fat that you eat is transported from the intestine to the rest of the body in chylomicron particles produced in the intestine. As the chylomicrons circulate through the blood stream, fat is removed and almost all -- 97 percent -- goes directly into your fat stores, those plump places around your waist, hips, and thighs. The fat-depleted chylomicrons become chylomicron remnants. Under normal conditions, chylomicron remnants are rapidly removed from the blood stream and broken down in the liver (good news). However, studies have shown that animals fed diets high in fat and saturated fat accumulate large amounts of chylomicron remnants in their blood. Because there are too many remnants for the body to dispose of quickly, they remain circulating in the blood for a period of time. Eventually they are oxidized and taken up by cells called monocytes, which lodge in the artery wall, causing atherosclerosis, or narrowing of the coronary arteries (bad news). So even if your total or LDL-cholesterol levels always read low, eating a diet high in fat and saturated fat can clog your arteries and put you at high risk for heart disease.
As if this isn't enough reason to eat a low-fat, low-saturated-fat diet, a study of healthy men and women with normal cholesterol levels who were fed high-fat and nonfat meals showed the harmful effect of a high-fat meal on artery function. The high-fat meal (450 calories of fat, 126 calories of saturated fat) used in the study consisted of an Egg McMuffin, Sausage McMuffin, and two McDonald's hash-brown patties. The oxidized triglyceride-rich lipoproteins formed as a result of eating so much fat prevented the arteries from relaxing or opening up normally following the meal. The effect lasted up to four hours and was not seen in people fed a low-fat meal. The effect on the artery wall is similar to that caused by high blood cholesterol or by smoking and is considered to be a precursor of atherosclerosis.
The bottom line is that a diet low in fat and saturated fat is heart-healthy, no matter if your cholesterol is sky-high or 170 mg/dL. And that's what this book is all about. Eater's Choice gives you the most effective, inexpensive, safe, and palatable way to lower your risk: change the foods you eat. YOU can stop clogging your arteries simply by eating a low-fat and low-sat-fat diet. YOU can make a difference in your heart's destiny.
By the time you finish this book, you should be convinced that it really does matter what foods you pour into your body. If you bought a new car and wanted to keep it in tiptop operating condition, you would never fill it with dirty gas oozing big globs of grease that could collect in the pipelines and clog the fuel line. You would make sure you fed it the best gas available. Why not treat yourself as well as you treat your car?
*This excerpt does not include figures and tables from Eater's Choice.