Experience the powerful benefits of Soy
by Patti Tveit Milligan, M.S., R.D.
The small soybean (about 1/4 inch) has been causing quite a stir in scientific circles
because of its potent phytochemicals and nutritional attributes.
The common soybean first became a food staple in ancient China
approximately 5,000 years ago. By the year 300 B.C., cultivation of
soybeans and their use as food spread to Korea, Japan, Southeast Asia,
and finally, about 1,000 years later, to Europe.
In the United States, health-conscious people have known for decades that soy foods are a delicious and healthful addition to the diet. Soybeans contain high amounts of protein, including all essential amino acids (the only such vegetable source). Soybeans are also a rich source of calcium, iron, zinc, phosphorus, magnesium, B vitamins, omega-3 fatty acids, and fiber. But what has most interested scientists in recent years is the discovery of non-nutritive phytochemicals in soy and their profound effect on human health.
Heart Health
Research on soy's benefits for the cardiovascular system started in 1909. For the past 20-plus years, the National Health Service in Italy has provided soy protein free of charge ot physicians who treat patients with high cholesterol.
Dr. James Anderson and his colleagues conducted a meta-analysis of soy protein on cholesterol reduction, published in The New England Journal of Medicine in 1995. Their research revealed several interesting findings. Out of 38 controlled clinical studies on soy protein consumption and serum lipids in humans, 34 demonstrated that cholesterol drops when soy is added or replaces animal protein. Including soy protein in the diet decreased cholesterol levels by an average of 13 percent, and LDL ("bad") cholesterol by 9.3 percent. This drop could mean as much as a 50 percent decrease in heart disease risk.
Soy protein was effective even in people who were already followig the American Heart Association's 30-percent fat diet. Soy protein appears to lower triglyceride levels while preserving HDL ("good") cholesterol.
The average consumption in these studies was 47 grams per day of soy protein, which is a considerable amount. One way to include this is to try a soy protein beverage or powder that adds 20 grams or so per serving.
The magnesium content in soybeans is important for the bones, arteries, and particularly the heart muscle.
Researchers Erdman and Potter in 1993 reported, in The American Journal of Clincial Nutrition, a 12 percent drop in cholesterol when 20 to 25 grams of soy protein and fiber were included in the diet. The solubel fiber in soybeans is known to block the absorption of cholesterol.
The accumulated evidence was enough to persuade the Food and Drug Administration (FDA) to allow heart-health benefits on soy labels (see sidebar below).
Soy supports cardiovascular health even beyond cholesterol control. Soybeans are a rich source of lecithin and vitamin E, natural antioxidants that protect against oxidation of LDL cholesterol. The magnesium content in soybeans is important for the bones, arteries, and particularly the heart muscle. Furthermore, genistein, a key isoflavone in soy, appears to reduce blood clotting. Blood clots may lead to heart attacks. Finally, genistein may prevent the multiplication of cells that make up artery plaque. While it may take two or more servings of soy per day to lower blood cholesterol levels, it may take only one serving a day to reduce blood clotting, plaque formation, and cholesterol oxidation.
FDA OK's heart health benefits on soy labels
The word is out: Soy food boost heart health. On October 26, 1999, the Food and Drug Administration (FDA) allowed food products containing soy protein to carry a label promoting soy's benefits for the cardiovascular system. Foods that contain at least 6.25 grams of soy protein per serving will be permitted to include information on their labels on soy's heart-protective properties. The effective amount of soy for this benefit is believed to be 25 grams a day.
Promising studies
In a University of Toronto study, middle-aged men and women ate modest amounts of soy foods over two one-month periods. Researchers found that soy reduced levels of LDL ("bad") cholesterol, while preserving HDL ("good") cholesterol. Cholesterol levels play a vital role in heart health.
In a second study, using the same subjects smaller amounts of the same soy foods prevented oxidation of LDL cholesterol. LDL oxidation damages the lining of the coronary arteries, which increases the risk of heart disease.
The FDA's rationale
The FDA states that its approval was based on evidence that soy protein - in a diet low in saturated fat and choelsterol - may help reduce the risk of heart disease. Foods eligible for the new labels include soy beverages, tofu, soybased meat alternatives, and some baked goods.
"Because soy protein can be added to a variety of foods, it is possible for consumers to eat foods containing soy protein at all three meals and for snacks," FDA officials noted. |
Protection against cancer
Excessive estrogen levels have been linked to breast, ovarian, uterine, and cervical cancers in women and prostate cancer in men. Estrogen levels may rise proportionately with the consumption of animal protein from livestock that were given hormones. Estrogen levels may also increase with the ingestion of pesticides, which have an estrogen base found in trace amounts of fruits and vegetables. Also, the increased incidence of obesity in Western culture plays a role in elevated estrogen.
Consumption of isoflavones may help prevent hormone-related cancers. It has been shown repeatedly that isoflavones can block the uptake of estrogen by estrogen-sensitive tissues, thereby acting as anti-estrogens. There is also evidence that they can inhibit the negative effects of androgens on the prostate gland.
Researchers have isolated two isoflavones, genistein and daidzein, adn are studying the cancer prevention and treatment properties of these compounds.
Genistein protects against breast cancer by blocking the more potent, cancer-causing human estrogen from entering breast cells. Genistein also prevents cancer-cell growth by inhibiting the activity of tyrosine protein kinase. This enzyme is created by oncogenes, genes that trigger the development of certain types of cancer.
Genistein sabotages other enzymes involved in cancer progression. In addition, it helps block angiogenesis - the spread of capillaries, stimulated by a malignant tumor, to nourish its cells and continue its growth. Angiogenesis is an essential step for the progression of cancer. If this step is successfully blocked, the tumor dies from starvation because its blood supply is cut off.
Clinical evidence
In one study, published in Nutrition and Cancer, researchers explored the effect of genistein on two different types of human lung cancer cells. They found that genistein blocked both types of cancer cells. Genistein activated certain genes that triggered the cancer cells' self-destruction.
One review points out that genistein has been proven to block the cell lines of several breast and prostate cancers. The author also states that soy exerts weak estrogen and anti-estrogen activity, and reduces elevated hormone levels. The reviewer concludes, "Collectively, these phytoestrogens, like genistein, have enough evidence to warrant their use in a number of clinical trials as a potential chemopreventive agent or adjunct to prostate cancer treatment."
One study investigated the relationship between soy milk and prostate cancer. This prospective trial focused on 225 cases of prostate cancer among 12,395 California Seventh-Day Adventist men. In 1976, they stated how often they drank soy milk. The researchers found that men who drank soy milk more than once a day had a 70 percent lower risk of prostate cancer than men who did not drink soymilk. The researchers concluded, "Our study suggests that men with high consumption of soy milk are at reduced risk of prostate cancer."
Genistein activated certain genes tha triggered the cancer cells' self-destruction.
In another study, researchers analyzed data from 60 women with breast cancer, and their individually matched controls. Overnight urine samples measured the women's excretion of daidzein, genistein, and other soy compounds. Researchers determined that the more soy the women consumed, the more soy constituents they excreted.
The women with breast cancer were found to have a lower excretion of soy compounds than the control group. The women who ate the most soy had about half the cancer risk as the women who ate the least amount of soy. The researchers concluded, "The results from this study support the hypothesis that a high intake of soy foods may reduce the risk of breast cancer."
In a study conducted at the University of Minnesota, genistein was used to combat BCP leukemia cells in mice. BCP leukemia is the most common form of cancer in children.
Daidzein has some of the same properties as genistein. These include antioxidant and chemopreventative activity, and the ability to make leukemia cells revert to normal cells.
Hormone-dependent cancers, such as breast, ovarian, and prostate, have responded especially well to a soy-rich diet or soy supplementation. While much promise exists with this important food source, more research is required to confirm the potential, far-reaching benefits in the treatment of all cancers.
Add more soy to your diet
Here are some soy foods you can easily add to your daily menu:
- Fresh green (immature) soybeans: They look like large pea pods; usually are salted and cooked until tender; called Edamame in Japanese restaurants or markets; make a delicious snack.
Tofu: Made from Soy milk to which a coagulating agent is added to separate the liquid into curds; many different textures, from firm to soft (for cooking) and silken (great for blending); many health food stores carry the low-fat version.
Tempeh: Made from whole-cooked soybeans and often with another grain such as barley; it has a dense, chewy texture; great for grilling or even in a sandwich or salad.
Soy milk: A combination of ground soybeans and water, used like diary milk; varies in protein and calcium content.
Textured vegetable protein: Made from soy flour that is compressed to change its texture to a dried, granular product; used as a meat extender and is the basis of many veggie burgers.
Soy flour: Basically has no starch because it contains no gluten; usually replaces only 15 to 25 percent of wheat flour in yeast-raised products.
Isolated soy protein: Made from defatted soy flour and is almost devoid of carbohydrates and fat; blends well with fruit shakes, muffins, pancakces, etc.
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Healthy bones
Osteoporosis is a worldwide disease. However, the United States has one of the highest rates of osteoporosis in the world, costing billions of dollars in health care and inestimable pain and debility. Osteoporosis is a disease in which bones become thin, brittle, and easily broken. Weight-bearing exercise and sufficient calcium and vitamin D help keep bones strong. Conversely, excess sodium and protein may have a negative effect on bone health, because they deplete calcium from the body.
Replacing animal foods with soy may help conserve the body's calcium stores and benefit the bones. Isoflavones in soy foods may actually slow the breakdown of bones and stimulate bone formation, although more research is needed to identify the exact mechanism.
Many soy foods are naturally high in calcium. Soy also contains magnesium and boron, which are important co-factors of calcium for bone health.
Daidzein is very similar to the drug ipriflavone, which is used throughout Europe and Asia to treat osteoporosis. In fact, Ipriflavone becomes most effective when it is metabolized. One of the byproducts of its metabolism is daidzein itself. (To learn more about ipriflavone and its benefits for bone health, read Build Bone Health: Prevent and Treat Osteoporosis, by Freedolph Anderson, M.D., with a forward by actress and women's health advocate Linda Evans. Green Bay: IMPAKT Communications, Inc., 1999.)
Recent studies have shown that genistein may have similar effects to estrogen in maintaining trabecular bone tissue. The spine has a high content of trabecular bone and is most sensitive to estrogen.
One compelling study, completed by Erdman, et al, focused on post-menopausal women who consumed 40 grams of isolated soy protein, containing 2.25 mg of isoflavones per gram of protein, every day for six months. Researchers found that these subjects significantly increased bone mineral density, as compared to the controls who were given 40 grams of casein/nonfat dry milk powder.
Daidzein is very similar to the drug ipriflavone, which is used throughout Europe and Asia to treat osteoporosis.
Easing menopausal symptoms
Symptoms that sometimes occur with menopause include night sweats and hot flashes. These are due to a loss of temperature control - one of the byproducts of a slowed production of estrogen. Because of their weak estrogen-like effects, soybean isoflavones may e an alternative way to control menopausal symptoms.
In Japan, where soy foods are commonly consumed daily, women are only one-third as likely to report menopausal symptoms as in the United States or Canada. In fact, there is no word in the Japanese language for "hot flashes." Even though their estrogen activity is weak, isoflavones may be potent enough to reduce menopausal symptoms. In fact, reasearch has shown that women who ate soy flour daily experienced about a 40 percent reduction in menopausal symptoms.
Powerful healing food
Keep in mind that isoflavones are present in all soy-containing foods, except for soy protein concentrates and isolates that have undergone alcohol extraction. In Japan, the average person consumes 20 to 100 mg of isoflavones per day from soy foods. It has been suggested that 50 mg daily or more of isoflavones would be prudent to consume through soy foods and/or a concentrated soy supplement.
The soybean may be small in size, but science is confirming that it packs a huge punch when it comes to protecting and enhancing your health. You can benefit in many ways to incorporating more soy and soy products into your diet.