By Jack Challem
Copyright © 1997 by Jack Challem, The Nutrition Reporter™.
All rights reserved.
Soybeans, used as a food for thousands of years in Asia, may turn out to be the ultimate women's health "supplement" of the 21st century.
Researchers have known that Asian women who eat traditional high-soy diets have a relatively low incidence of reproductive and hormone-related disorders, including menopausal hot flashes, osteoporosis, and breast cancer. They are also less likely than American and European women to develop coronary heart disease.
In fact, soy-eating Japanese women so rarely experience menopausal hot flashes, a sign of volatile estrogen levels during menopause, that there is no traditional Japanese word to describe the sensation, according to Marcus Laux, N.D., coauthor of Natural Woman, Natural Menopause (HarperCollins, 1997).
Although genetics might account for some of the differences between Asian and American women, scientists have pointed out that Asian women's risk of "female" disorders increase when they move to the United States and adopt low-soy diets.
"The American diet's much higher fat content compared to the Asian diet was initially considered the most important factor leading to increased cancer risk in Americans, that is, suggesting that fat is cancer-causing," explained Stephen Barnes, Ph.D., who researches soy at the University of Alabama at Birmingham. But, added Barnes, "A new hypothesis is being examined to determine whether one or more components of the Southeast Asian diet are cancer-preventing."1
Isoflavones May Reduce Breast Cancer Risk
What nutritional secrets do ancient soybeans hold for women today?
Many researchers believe their most beneficial components are a group of nutrients called isoflavones, related to the more common flavonoids found universally in plants. Flavonoids help regulate the growth of plants and protect them from stress and the damaging effects of ultraviolet radiation.
Earlier this year, Catherine Rice-Evans, Ph.D., of the International Antioxidant Research Centre at Guy's Hospital, London, reported that genistein, the most studied isoflavone, had the greatest antioxidant activity of these compounds. Daidzein was the second most powerful antioxidant isoflavone.2 Antioxidants, of course, protect the body from cell-damaging molecules known as free radicals, which accelerate the aging process, initiate many cancers, and exacerbate diseases in general.
As an antioxidant, genistein plays multiple roles. It boosts the body's production of superoxide dismutase (SOD), another powerful antioxidant.3 Genistein also functions a lot like SOD, preventing cancer-causing mutations to deoxyribonucleic acid (DNA), according to research conducted at the Mount Sinai School of Medicine, New York.4
But genistein and the other isoflavones protect against breast cancer in other ways as well.
"The isoflavones contained within soy are among the most versatile biopharmaceuticals known to man," Stephen Holt, M.D., of Fairfield, N.J., told Let's Live. Holt, author of Soya for Health: The Definitive Medical Guide (Mary Ann Liebert Publishers, 1996), added, "These are safe foods that have been used for thousands of years in Asia. Isoflavones account, in part, for the major differences in disease between East and West."
Very Weak Plant Estrogens
In addition to being antioxidants, all of the isoflavones are very weak plant versions of estrogen, the hormone that "feminizes" women. (Men also produce of estrogen, though in smaller quantities - see box.) For example, genistein has 1/1,000th the estrogenic activity of the actual female hormone.
This estrogenic activity may be the principal reason why genistein and the other isoflavones protect against breast cancer, according to David T. Zava, Ph.D., of the Cancer Research Division of the California Public Health Foundation, Berkeley. The hormone estrogen is known to trigger cell growth, which is needed for reproduction, growth, and healing. But too much estrogen can also cause abnormal cell proliferation and increase a woman's risk of breast and endometrial cancers.
As very mild estrogens, genistein and the other isoflavones strike a biological balance. They readily attach to the estrogen receptors of cells, kind of like a key entering a lock. Isoflavones seem to promote some of the beneficial effects of estrogen, such as increasing bone density and, the evidence suggests, preventing osteoporosis.
However, when isoflavones attach to cell receptors, they form an obstacle to other estrogens, much the way only one key can enter a lock at any given time. In doing so, isoflavones block more potent hormonal estrogen from attaching to cells and signaling them to to initiate cancerous cell behavior, according to a recent article by Zava in the journal Nutrition and Cancer. Genistein could be used to "prevent symptoms and diseases associated with estrogen deficiency, and as a growth regulator, to prevent and inhibit the growth of estrogen-sensitive and estrogen-independent cancers," he explained 5
"Genistein is the most beneficial thing in soy - there's no question about that," Zava said in an interview.
Genistein may also provide similar protection against synthetic estrogen-like compounds, such as those found in pesticides, according to Devra Lee Davis, Ph.D., of the World Resources Institute, Washington, D.C. Several years ago, Davis theorized that many breast cancers are the result of estrogen-mimicking pesticides, which amplify the negative effects of hormones. In a recent issue of Science & Medicine, she pointed out that genistein helps the body dispose of these pesticide byproducts.6
And not all of genistein's effects are related to its antioxidant and mild estrogenic properties. Zava pointed out that genistein's anticancer action may be because it inhibits tyrosine kinase, an enzyme involved in cancer proliferation, and in blocking angiogenesis, the tumor-dependent growth of blood vessels.
Isoflavones Ease Menopausal Symptoms
Several studies, presented last September at the Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, in Brussels, Belgium, noted that isoflavones might be a safe alternative to estrogen-replacement therapy, which can increase a woman's risk of breast and endometrial cancer.
Gregory L. Burke, M.D., of the Bowman Gray School of Medicine, Winston-Salem, N.C., described a study of menopausal women who were given soy protein supplements rich in isoflavones for six weeks. While the women continued to have menopausal symptoms, the intensity of their hot flashes and night sweats decreased significantly.7,8
In another presentation, John A. Eden, M.D., of the Royal Hospital for Women, Paddington, Australia, reported the dramatic reduction in menopausal hot flashes among nine women given 160 mg of isoflavones daily. When they began the study, the women had an average of 6.7 hot flashes daily. But the time the study ended, 12 weeks later, the average number of hot flashes had dropped by about half, to 3.4 daily.9
The isoflavones also forestall osteoporosis, which physicians believe is caused, at least in part, by low postmenopausal levels of estrogen. In a recent animal experiment, Bahram H. Arjmandi, Ph.D., of the University of Illinois, Chicago, stopped estrogen production in a group of laboratory rats by removing their ovaries (the glands that produce the hormone). The lack of estrogen prompted a decrease in bone density in the animals, according to an article by Arjmandi in the Journal of Nutrition. However, animals fed soy protein, rich in isoflavones, maintained their bone density.10
The benefits seem to translate to people. In a study at La Sapienza University, Rome, Italy, physicians and researchers gave 40 postmenopausal women either calcium supplements or calcium supplements combined with ipriflavone (a synthetic isoflavone). After 12 months, spine and forearm bone density decreased among the women taking only calcium. However, bone density increased among the women taking the calcium/ipriflavone combination, according to an article in the journal Calcified Tissue International.11
"Soy isoflavones act like weak estrogens in respect to bone metabolism," explained Susan M. Potter, a nutrition professor at the University of Illinois, Urbana. "Maybe postmenopausal women can use soy products instead of estrogen replacement. Maybe women at risk for breast cancer can tolerate this better than other estrogens."
In a more recent report, presented at the soy conference In Brussels, John W. Erdman, Ph.D., of the University of Illinois, Urbana, described another study on isoflavones in the treatment of osteoporosis. Sixty postmenopausal women were given supplements containing either 55.6 or 90 of isoflavone-rich soy protein or a placebo daily for six months. Women consuming the higher amount of isoflavones benefited from significant increases in bone mineral content and density in their lumber spines.12
Lowers Heart Disease Risk
A number of studies have shown that soy isoflavones (and possibly other components of soy, e.g. proteins, saponins, and lignans) can reduce a woman's risk of coronary heart disease. Heart disease, not breast cancer, is the leading cause of death among American women.
The University of Illinois' Potter has pointed out that soy foods can lower cholesterol levels. How it accomplishes this is still uncertain, though she has suggested that may work through a number of mechanisms. For example, soy increases the excretion of bile. "The physiological result of this creates an environment in which cholesterol is being 'pulled' from the body," Potter explained.13
Soy also affects hormone production in the body. Potter cited research suggested that soy feeding in animals often creates metabolic effects similar to those of hyperthyroidism, including weight loss. In addition, soy seems to lower levels of insulin, high levels of which are strongly associated with risk of heart disease.
Two recent studies further elaborated on the role of soy isoflavones in the prevention of heart disease. In one, Michael G. Kinsella, Ph.D., of the University of Washington, Seattle, found that genistein selectively inhibited the growth of smooth muscle cells in arteries. Smooth muscle cell proliferation is strongly linked to heart disease.14
In the other study, J. Koudy Williams, D.V.M., of the Bowman Gray School of Medicine, fed 22 rhesus monkeys diets with two kinds of soy protein, one rich in isoflavones and the other devoid of these nutrients. The monkeys eating an isoflavone-rich diet maintained normal heart function when Williams gave them a stimulant, whereas the monkeys eating the isoflavone-deficient diet developed heart irregularities. The effect was so dramatic that Williams and his colleagues observed that "a dietary supplement [of soy] potentially may provide a viable alternative to traditional [estrogen] hormone replacement therapy."15
Furthermore, there's intriguing evidence from animal experiments hinting that early consumption of genistein can reduce the risk of cancer later in life. Coral A. Lamartiniere, Ph.D., of the University of Alabama, Birmingham, fed genistein to rats before they entered puberty and were exposed to a known cancer-causing chemical. According to Lamartiniere's article in the journal Carcinogenesis, rats receiving genistein developed half the tumors compared with rats given a placebo.16 Other studies have shown that Asians' life-long consumption of soy mght keep their cancer risk low.
Overall, research on the health benefits of soy isoflavones has excited research by the simplicity of its message: a single food may prevent many of the diseases, from menopausal problems to breast cancer, associated with high or erratic estrogen levels. That raises the possibility that the American diet is fundamentally unbalanced and that adding soy foods may restore many beneficial nutrients, including the isoflavones.
"Adding soy to the diet can do only good things," Gregory L. Burke, M.D., said. "It is a reasonable and prudent addition to the diet."
A related article...
Men Also Benefit from Soy
Women aren't the only beneficiaries of soy isoflavones. These remarkable nutrients may also reduce the risk of prostate cancer in men.
Japanese men consume substantially more soy products than do Western men, and their blood levels of isoflavones are up to 110 times richer in these nutrients. A number of studies have found that genistein inhibits the growth of tumors dependent on male hormones. According to Herman Adlercreutz, M.D., of the University of Helsinki, the high life-long isoflavone levels found in Japanese men may account for their relatively low risk of death from prostate cancer.
How would isoflavones help men? According to Wing-Ming Keung, Ph.D., of the Harvard Medical School, these nutrients inhibit the activity of enzymes involved in the breakdown of steroid hormones, including testosterone.
A related article...
Soy Foods Taste Better Than They Used To
If you haven't tried any soy foods in a while, you're in for a pleasant surprise.
Years ago, soy burgers conjured up images of emaciated vegetarians eating tasteless tofu. Today, the selection and taste of soy foods is nothing less than titillating to the senses - even to die-hard meat eaters.
Many health food stores carry several brands of soy burgers and soy hot dogs. Cook one up, add some mustard and onions, and throw it on a bun - and you'll be amazed at how "real" they taste. Likewise, several companies offer chicken look-alike products made from textured soy protein. You can wash them down with various flavors of soy "milk." Consider a thick vanilla type - it's reminiscent of a rich milk shake.
According to some experts, such as David T. Zava, Ph.D., fermented soy foods, such as miso and tempeh, may be the most healthful soy foods. That's because beneficial bacteria help break down large carbohydrate molecules and release more that contain genistein. But if you have a healthy digestive tract, your body's own bacteria can do the same thing. - JC
1 Barnes S, et al., "Rationale for the use of genistein-containing soy matrices in chemoprevention trials for breast and prostate cancer," Journal of Cellular Biochemistry, 1995; Suppl 22:181-187.
2 Ruiz-Larrea MB, et al., "Antioxidant activity of phytoestrogenic isoflavones," Free Radical Research, 1997;26:63-70.
3 Cai Q and Wei H, "Effect of dietary genistein on antioxidant enzyme activities in SENCAR mice," Nutrition and Cancer, 1996;25:1-7.
4 Wei H, et al., "Inhibition of UV light- and Fenton reaction-induced oxidative DNA damage by the soybean isoflavone genistein," Carcinogenesis, 1996;17:73-77.
5 Zava DT and Duwe G, "Estrogenic and antiproliferative properties of genistein and other flavonoids in human breast cancer cells in vitro," Nutrition and Cancer, 1997;27:31-40.
6 Davis DL, et al., "Environmental influences on breast cancer risk," Science & Medicine, May/June 1997:56-63.
7 Burke GL, "The potential use of a dietary soy supplement as a post-menopausal hormone replacement therapy," Program & Abstract Book, Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Sept 15-18, 1996, Brussels, Belgium: 40-41.
8 Haney DQ, "Study: Tofu may ease menopause," Associated Press, Nov. 10, 1996.
9 Eden J, et al., "Hormonal effect of isoflavones," Program & Abstract Book, Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Sept 15-18, 1996, Brussels, Belgium: 41-42.
10 Arjmandi BH, et al., "Dietary soybean protein prevents bone loss in an ovariectomized rat model of osteoporosis," Journal of Nutrition, 1996;126:161-167
11 Valente M, et al., "Effect of 1-year treatment with ipriflavone on bone in postmenopasual women with low bone mass," Calcified Tissued International, 1994, 54:377-380.
12 Erdman JW, Stillman RJ, Lee KF, Potter SM, "Short-term effects of soybean isoflavones on bone in postmenopausal women," Program & Abstract Book, Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, Sept 15-18, 1996, Brussels, Belgium: 21.
13 Potter SM, "Overview of proposed mechanisms for the hypocholesterolemic effect of soy," Journal of Nutrition, 1995;125:606S-611S.
14 Schönherr E, et al., "Genistein selectively inhibits platelet-derived growth factor-stimulated versican biosynthesis in monkey arterial smooth muscle cells," Archives of Biochemistry and Biophysics, 1997;339:353-361.
15 Honoré EK, et al., "Soy isoflavones enhance coronary vascular reactivity in atherosclerotic female macaques," Fertility and Sterility, 1997;67:148-154.
16 Murrill WB, et al., "Prepubertal genistein exposure suppresses mammary cancer and enhances gland differentiation in rats," Carcinogenesis, 1996;17:1451-1457.
This article originally appeared in The Nutrition Reporter™ newsletter. The information provided by Jack Challem and The Nutrition Reporter™ newsletter is strictly educational and not intended as medical advice. For diagnosis and treatment, consult your physician.