The Soy Renaissance
In my best-selling book the Soy Revolution (www.amazon.com), I revered the general health value of the inclusion of soy in many Western diets. There has been a number of issues raised about the health benefits of soy, but I have an opinion that much of this “back chat” that denies the health benefit of soy comes from lobbying for the meat and dairy industry. That said, I am not a “soy nut” and traditional diets which contain meat, dairy or fish protein can be healthy. Much of the health value of soy beans are to be found in an interesting medicinal series of components called isoflavones.
Phytoestrogens from Several Sources (“Plant Hormones”)
Isoflavones are an example of a category of natural substances that have been called phytoestrogens (phyto = plant). These plant compounds are considered to have estrogen hormone-like effects, but this is a naïve viewpoint concerning the actions of these potent and versatile natural substances. Phytoestrogens have many biological effects and they are best viewed as adaptogens or biological-response modifiers, rather than “simple estrogens.”
The most abundant and common source of isoflavones are soybeans which contain the isoflavones named genistein, daidzein and glycetein. Other examples of phytoestrogens are found in red clover (isoflavones), lignans, or fruit or grain fibers and phytosterols. Phytosterols are present in several beans, cereals or grass sprouts. Some grain fibers contain hormone-like substances that are converted to enterolactones, yet another a form of phytoestrogens.
Active occurring phytoestrogens are transformed by bacteria in the colon or body enzyme systems into isoflavones or related compounds with estrogen-balancing effects. These isoflavones include compounds, such as genistein, daidzein and equol which themselves have active metabolites (chemically converted substances), e.g. daidzein sulphate. I do not wish the reader to get bogged down in scientific terms, but knowing simple things about isoflavone chemistry can aid in understanding the benefits of these natural substances for menopause and common menstrual problems. The subject of phytoestrogens has been somewhat oversimplified by the dietary supplement industry and somewhat misunderstood by some physicians and patients.
Population studies of women with menopausal symptoms provide convincing evidence that soy foods containing isoflavones (phytoestrogens) may reduce the occurrence or severity of hot flashes and other symptoms of menopause. Women on traditional soy-enriched diets in Japan have generally much higher levels of measurable phytoestrogens in their urine than women in Western societies who eat a Standard American Diet (SAD). Coincidental with this finding of high isoflavone intake in the diet are reports of significantly less symptoms of menopause, especially a low occurrence of hot flashes in these Oriental women. This beneficial effect of soy has been attributed to the presence of the isoflavones genistein and daidzein in soybean foods; and these isoflavones have been concentrated from soybeans and placed in many dietary supplements that are used for menopause and PMS management. I developed one of the first soy isoflavone concentrates that was sold as a dietary supplement in the U.S. in 199 (www.naturalclinician.com).
Isoflavones Combat Hot Flashes
There are more than twenty recent clinical trials that have tested the ability of soy isoflavones, taken in concentrated formats (in pills or in soy protein isolates), to reduce hot flashes in women during the climacteric. While results have been mixed, about one-half of the subjects in these trials reported improvements in hot flashes over a relatively short term of study (a few weeks in most cases).
There has been much variation in the dosage of isoflavones used in these studies, together with variations in the characteristics of the women studied. I believe that the beneficial effects of soy isoflavones are somewhat dose-dependent in many women (how much is taken on a daily basis). In other words, in studies where soy isoflavones failed to reduce symptoms of menopause or PMS, there may have been an inadequate amount of isoflavones used in the studies. In my opinion, total daily intakes of more than a range of 80-100 mg. of isoflavones in a pill should be avoided, except under medical supervision.
Soy isoflavones belong to a group of natural antioxidant compounds found in nature. Isoflavones have varying potency in terms of an estrogen-like action. However, they are all weak estrogens or modulators of estrogen’s effects on the body. I have been impressed by the benefits of using isoflavones of different origins together in dietary supplements. With these combinations, additive benefits are seen and lower dosages of each isoflavone can be used together for greater effects (synergy) . In particular, the combination of isoflavones of soy with isoflavones from red clover may be more effective at dealing with symptoms of menopause such as hot flashes, in comparison to the use of one type of isoflavone alone. This is an example of synergy in supplement formulations and synergistic combinations are the basis of modern approaches to supplement formulation.
There is a long history of precedent for the safety of soy foods and their isoflavone content. There are no studies in humans that have shown clear or significant adverse effects of soy isoflavones, even when taken in relatively large doses of a total daily intake of 100 mg. or more. While some studies in animals have shown that estrogenic properties of isoflavones can cause estrogen-sensitive tissues or estrogen-sensitive cancer to proliferate, there is no evidence that soy isoflavones have caused breast or other types of cancer in humans or evidence of spontaneous cancer formation in animals. In fact, a review of the medical and scientific literature suggests that isoflavones in soy may exert significant cancer-protective effects in both animals and humans. (See Holt, S., “The Soy Revolution,” Dell Publishing, N.Y., N.Y., 2000). I believe that soy food prevents breast cancer, especially when given early in life.
Do Phytoestrogens Cause Cancer?: Soy Safety
Several types of cancer are estrogen-dependent. This means that the hormone estrogen can drive the growth of certain types of cancer, especially common types of breast cancer. Many women question whether or not plant estrogens (phytoestrogens) cause cancer. These questions are particularly relevant in women with an enhanced risk of breast cancer or a history of breast cancer. Scientists have attempted to address the safety of phytoestrogens in relationship to cancer, but there are many different types of these plant compounds. Furthermore, certain phytoestrogens have many beneficial effects on the body, especially when body estrogen levels are high independent of any actions on estrogen receptors (estrogenic actions in the body). It seems likely that the body’s response to plant estrogens is controlled by many factors including: the strength of the estrogenic stimulus, genetic factors and the presence of other factors that may promote or inhibit cancer development.
Research suggests that the duration of exposure to estrogens over a woman’s lifetime is important in the propagation of cancer. However, there is no evidence that any phytoestrogens, used in popular dietary supplements, can cause or worsen cancer. In contrast, several studies show a cancer-preventive action of common phytoestrogens such as soy isoflavones. These findings were apparent in the famous “China Study”, directed by T. Colin Campbell. Much concern has focused on soy and the development of breast cancer but soy food consumption has not been shown to increase the risk of breast cancer in humans and soy in the diet is not known to adversely affect survival in patients with breast cancer. Quite to the contrary, landmark studies in animals have shown that soy diets can prevent breast cancer, especially when soy is given early in life.
The Isoflavone Debate
The confusion surrounding the roles of isoflavones in cancer inhibition and/or promotion is attributable, in part, to the current lack of knowledge about their biological actions. For example, one simplistic and misleading idea about these compounds is that they are phytoestrogens with unqualified estrogenic effects. While isoflavones have an affinity for estrogen receptors, they tend to exert lower levels of estrogenic stimuli to cells than the body’s own estrogens (e.g., 17-beta-estradiol). This means simply that isoflavones may serve as a “balancing act” for the effects of endogenous estrogens on body tissues. These observations imply that soy isoflavones can act as a “biochemical adaptogen” or a kind of “biological response modifier,” especially related to estrogenic status. In some circumstances, soy isoflavones have an overall anti-estrogenic effect on the body (when body estrogen levels are high), whereas in others, they exert weak estrogenic actions—this is their balancing quality.
Recent work suggests that soy isoflavones can exert estrogenic effects by altering the metabolism of the body’s own (endogenous) estrogenic compounds. As mentioned, isoflavones do not have a consistent pro-estrogenic action, and when they occupy estrogen receptors, they can block the action of more potent endogenous estrogens, thereby making their overall effect antiestrogenic, particularly in states of estrogen dominance. However, these circumstances surrounding these potential modifying roles of isoflavones on body chemistry are not simple and they require further scientific exploration. In this dialogue, I use the terms adaptogenic and biological response modification in a synonymous, but arguably inaccurate manner.
Soy isoflavones may exert anticancer benefits because of their function as potent antioxidants and free radical scavengers. Animal experiments and limited human observations show that isoflavones exert an antiangiogenic effect, which is an important step the growth and progression of cancer (and other chronic diseases). Antiangiogenesis is the inhibition of unwanted blood supply to diseased tissues or cancer. Also, the specific isoflavone genistein can interfere with key enzymes involved in cell proliferation and tumor growth. Various isoflavones inhibit tyrosine kinase and deoxyribonucleic acid (DNA) topoisomerase. This latter enzyme is involved in cellular apoptosis (cell changes related to cell death). Thus, soy isoflavones have potential anticancer effects that act independently of any estrogenic or antiestrogenic activity. These issues have been ignored or purposely forgotten by the purveyors of “anti-soy propaganda.”
Soy isoflavones appear to be quite safe when used in doses with an existing precedent for safety (up to approximately 80-100 mg of total soy isoflavones in dietary supplements). While it is unlikely that anyone would consume more than a total daily intake of 150 mg. of isoflavones, even if he or she ate a heavily soy-enriched diet, isoflavone supplements are available in a variety of doses. I repeat that continuous use of soy supplements with high dosages of soy isoflavones should be avoided (>80-100mg of total isoflavones per day).
The complex, beneficial actions of isoflavones and other components of soy make soy foods valuable for use in the metabolic Syndrome X. For a more complete account of the positive impact of soy diets on health, readers are referred to three of my books (“The Soy Revolution,” Dell Publishing, N.Y., 2000; “Soya for Health,” Mary Ann Liebert Publishers, N.Y., 1997; and “Combat Syndrome X, Y and Z …”, www.stephenholtmd.com, N.J., 2002).