Soy and The Heart: Atherosclerosis May Be a Self-Inflicted Disease

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Soy and The Heart: Atherosclerosis May Be a Self-Inflicted Disease

In Japan, only 238 men and 121 women per 100,000 succumb to heart disease, roughly half the number in the United States.

Japan has the lowest rate of death from heart disease in the world for men and the second lowest for women. (The mortality rate is slightly lower for women in France.) The traditional Japanese low-fat, soy-based diet appears to be a major factor. Recent studies show that soy may have some unique properties that make it a potent "heart protector."

Atherosclerosis

Atherosclerosis is a progressive disease that often begins in childhood and can lead to coronary artery disease, the cause of most heart attacks. The arteries delivering blood and oxygen to the heart become clogged with plaque, a yellowish, waxy substance.

Plaque starts off as fatty streaks in the arteries -- in the United States these fatty streaks can appear in children as young as 10 years old! Eventually plaque deposits can become big enough to close off the artery. A reduction in the flow of oxygen and blood to the heart can cause angina, or chest pain.

A heart attack occurs when the heart muscle dies or is damaged owing to a lack of nourishment. In some cases, severe atherosclerosis can weaken the artery, resulting in a stretched-out portion called an aneurysm, which can cause a rupture in the wall.

Another theory is that plaque is similar to a cancerous tumor that grows out of control. Some people believe that a chemical or virus may trigger this in uncontrolled growth. However, there is strong evidence that atherosclerosis is directly related to the balance between particular types of lipids or fat in the blood.

Blood Lipids

Lipids are a form of fat found in the blood. Fat has become a dirty world of late, yet it is essential for life. In fact, a woman's body may be composed of from 25 to 35 per cent fatty tissue; a man's body has only about 10 per cent less. Fat is an important source of energy. Body fat protects and insulates body organs; it carries fat-soluble vitamins through the body; and it is essential for the production of sex organs. Blood is basically water, and since oil and water don't mix, fat travels through the bloodstream on molecules called lipoproteins.

Cholesterol

Cholesterol is a lipid that is produced by the liver and is present in foods of animal origin, such as meat and full-fat dairy products. Since cholesterol is basically a fat, it is carried through the body as a lipoprotein. Cholesterol is used by the cells for energy, cell repair, manufacture of sex hormones and other important jobs.

High-density lipoprotein (HDL) is often called "good cholesterol" because it helps rid the body of excess cholesterol. Low-density lipoprotein (LDL), the body's major carrier of cholesterol, is often called "bad cholesterol" because it is believed to be responsible for the formation of plaque.

Cells have special binders or receptors that latch on to LDL as they need it. When the cells have enough cholesterol, they stop producing receptors, allowing the LDL to circulate in the bloodstream. Many researchers believe that too much LDL in the blood can cause injury to the artery wall, triggering the formation of plaque.

Soy also appears to reduce levels in patients with normal cholesterol, although not as dramatically as in patients with high cholesterol. Under the direction of K.K. Carroll of the University of Western Ontario, researchers examined the effect of soy protein on women with normal blood cholesterol. Female students were put on two different dietary protocols. The first consisted of a normal, well-balanced diet in which protein came from both animals and plants; the second was a standard diet with an exception: the protein portion was derived from soy products. Meat was replaced with soy analogues and milk was replaced with soy milk. The fat composition of the diet (roughly 40 per cent of the total daily calories) remained the same on both regimens. While on soy protein, the students' average cholesterol levels dropped by about five per cent. It was noted that although soy protein appears to work more dramatically in people with elevated cholesterol levels, it also worked well in people with normal blood lipid levels.

The Diet Connection

After World War II, when the rate of heart disease continued to soar in Western countries, researchers began to wonder why certain nationalities appeared to be immune to this problem.

They began to seriously consider possible factors for the difference. Diet appeared as the most striking and consistent. In countries where the intake of fat was high -- particularly in the form of saturated fat from meat or dairy products -- deaths from heart disease soared. However, in countries where the fat intake was low and the diet was high in vegetables and grain, the rate of heart disease was also low.

Some researchers clung to the belief that lucky people must be genetically predisposed to low cholesterol levels and low risk of heart disease. However the ongoing Ni-Hon-San study, which began in 1965, showed that the problem was not in genetics but in what the group was eating.

Researchers observed the diets of three groups of Japanese men. The first group lived in Japan and ate the traditional Japanese diet consisting of seven per cent saturated fat daily. The second group were men who had moved to Honolulu, where their eating habits became more Americanized (consuming about 12 per cent saturated fat daily). The third group were men who moved to San Francisco and whose diets contained 14 per cent saturated fat per day.

Ten years later the men who stayed in Japan had the lowest cholesterol levels and the healthiest hearts. Those Japanese who moved to Honolulu had cholesterol levels that were 12 per cent higher than the men in Japan and had a higher rate of heart disease.

The Japanese in San Francisco fared the worst with a 21 per cent higher heart disease rate than those in Japan. There is no doubt that some foods can promote high blood cholesterol and that other foods can lower it.

Many studies have shown that soy is a potent cholesterol buster. Most have shown that soy can play a significant role in lowering cholesterol levels. In one experiment, patients with high cholesterol were given soy protein instead of animal protein along with an additional 500 mg of cholesterol daily in the form of egg powder. Interestingly, despite the added cholesterol, the group showed a dramatic decline in total cholesterol levels. The addition of cholesterol to the diet did not appear to interfere with the ability of soy to cut cholesterol levels.

Children at Risk

Soy can also reduce cholesterol in children. In rare cases children are born with a genetic tendency to develop extremely high cholesterol. In a recent study involving 11 children with very high cholesterol, researchers found that isolated soy protein could reduce blood cholesterol and LDL, or "bad cholesterol," levels more effectively than a standard low-fat diet.

For two months the children ate a standard diet, resulting in a 14 per cent drop in total cholesterol and a 17 per cent drop in LDL cholesterol. When isolated soy protein replaced animal protein in their diets, the cholesterol levels dropped even further (32 per cent from the start of the diet) and LDL cholesterol fell an additional 20 per cent to a 37 per cent total reduction.

This study is extremely important because if their cholesterol levels went unchecked, these children could be at an extremely high risk of developing heart disease.

Genistein, an isoflavone found in soy, is believed to inhibit the action of enzymes that may promote cell growth and migration. Some researchers speculate that by blocking the action of these enzymes, genistein may also prevent the growth of cells that form plaque deposits in arteries, much the same way that genistein may prevent the growth of tumors.

Researchers suggests that the combination of amino acids found in soy may alter a step in the manufacture of cholesterol. Some studies have shown that after eating soy protein, blood glucagon levels may alter the activity of coenzyme A, which is necessary for the synthesis of cholesterol.

Estrogenic Effect

There is speculation that the phyto-estrogens in soy may exert an estrogenic effect on the body that lowers cholesterol. Estrogen plays a major role in the way lipids are produced, handled, broken down and eliminated from the body. Studies show that after menopause, when a woman's estrogen levels drop, cholesterol levels typically rise, along with risk of developing coronary artery disease. However, women who have estrogen-replacement therapy experience a dramatic drop in LDL and a rise in HDL.

Other studies have shown that estrogen increases the number of LDL receptor in cells, which means that less cholesterol is left circulating in the blood. All of these factors lead researchers to wonder whether soy's ability to lower LDL and cholesterol is related to its estrogenic activity.

Thyroid Connection

Studies have also found that soy can raise blood plasma levels of thyrioxine, a hormone produced by the thyroid gland, while at the same time lowering blood cholesterol. These studies show that an increase in thyroxine always precedes the drop in cholesterol.

People who have underactive thyroid glands (hypothyroidism) tend to have high levels of blood cholesterol. Therefore, researchers hypothesize that soy may somehow stimulate the thyroid gland to produce more hormone.

Researchers also suggest that soy somehow binds with bile in the intestine and is excreted in the feces. The liver compensates by producing more bile salts, which requires cholesterol, reducing the amount of circulating cholesterol.

Soy protein has lower levels of certain essential amino acids than animal protein, such as lysine and methionine. When lysine is added to a soy diet, the level of LDL rises. The mix of amino acids in soy may prevent the formation of plaque.

Soy Protection

- Researchers have isolated compounds in soy that may prevent heart disease by altering blood lipid levels.

- A soy-based diet may indirectly protect against heart disease because it tends to be lower in fat than food from animal sources. (Studies show that a high-fat diet is a major risk factor for heart disease.)

Recommended Reading:

Soy City Foods Vegetarian Cookbook

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by The Vegetarian Restaurant 144 pp (sc) $21.95

Reversing Heart Disease

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by J Whitaker, MD 371 pp (sc) $14.99

Earl Mindell's Soy Miracle

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by E Mindell 256 pp (sc) $16.00

Canadian Health Reform Products Ltd.

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By Earl Mindell

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