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Dr. Bernard Presser D.C.
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There has been a deluge of "positive information" promoting claimed health benefits of soy. In the form of food and as fractionated supplements, soy and its phytoestrogens or isoflavones are being sold as miracle makers. Soy is touted as a quality protein food to replace items such as meat, fish, poultry, eggs, and milk. Studies report it can lower cholesterol and thus the risk of heart disease; reduce risk of diabetes; protect against some forms of cancer; that for women it can prevent breast cancer, reduce hot flushes, relieve vaginal dryness, and strengthen bones; that for men, it can prevent prostate cancer. This "wonder food" is said to be high in protein (containing all essential amino acids) and containing potassium, iron, calcium, copper, zinc, magnesium, carotene, niacinamide, vitamins B1, B2, B6, folic acid, and even B12. It is low in sodium, low in fat, and high in fiber. Soy is about 38% protein and 18 to 20% fat - primarily polyunsaturated with very little saturated. It is supposed to be an ideal food!
There are now more than 2000 soy products on the market. No longer just a "health food store" staple, even supermarkets carry soy milk, soy yogurt, soy cheese, soy sausages and bacon and hot dogs, soy flour, soy nuts, soy-based cereals, soy protein bars, soy drinks, and textured vegetable protein (TVP) - a meat substitute for everything from veggie burgers to ‘fish' fingers. Soy protein isolates are found in protein powders and energy drinks. Tofu, tempeh, soy sauce, and a few other traditional forms of soy are gaining popularity too. Soy oil is used in numerous processed foods from salad dressing and mayonnaise to cookies and bread. Soy-based infant formulas are widely used. Even Dr. Barry Sears, famous for his "Zone" diet books, has written The Soy Zone for vegetarians. He suggests that all rice, cereals, pastas, breads, other grain products, potatoes, and sugary products be replaced with soy flour, soy grits, textured soy protein, soy cheese and yogurt, soy milk, and soy on. Wholesale sales of soy flour and soy protein isolates alone more than doubled between 1980 and 1996, growing from $119.47 million to $293.39 million.
Soybeans originated in the Orient. During the Chinese Chou Dynasty (1134-246 BC), plants were classified in terms of both food and medicinal value. The soybean was designated one of the five sacred and principal crops along with rice, wheat, millet, and barley. But the pictograph for the soybean indicates that it was not initially used for food. Rather than showing the seed and stem structure of the plant as was done for the other grains, the root structure is emphasized. Soy's roots, more than other leguminous plants, can feed the soil. The nodules are storehouses of nitrogenous bacteria which disperse as the roots rot. So growing soy replenishes soil impoverished by such "greedy" plants as wheat or maize, and can serve as a green manure crop.
It was not until the third century B.C. that the soybean truly began to be used as a food. Soybeans were boiled to make them palatable but were generally scorned because they produced flatulence and were used only by the poor except in years of famine when other people would be forced to eat them. Soon, the Chinese perfected the technique of fermenting soybeans. Fermented forms gained acceptance since they can be digested and health benefits can be observed. Products such as tempeh, natto, miso, and shoyu (soy or tamari sauce) were the first soy foods. Use of young soybean sprouts for febrile diseases and Summer Heat patterns is a minor part of traditional Chinese medicine. Later, Chinese scientists discovered that a puree of cooked soybeans could be precipitated with calcium sulfate or magnesium sulfate (plaster of Paris or Epsom salts) to make a smooth pale curd - tofu or bean curd. Use of fermented and precipitated soy products then spread to other parts of the Orient including Japan and Indonesia.
Bland, precipitated products like tofu account for about 90% of the processed soybeans consumed in Asia today. The increased use of bean curd as a source of protein has not necessarily been a healthful trend. Tofu and similar products are refined and processed, but they are certainly not nutritionally dense. It is estimated that protein from soy foods makes up 20% to 60% of the daily protein intake of Southeast Asians. Soy foods did not make an inroad into the western diet until the 18th century. By 1890, soybeans were being grown all over the U.S. more for animal fodder and soy oil than anything else. And Americans produce primarily yellow soybeans whereas the ancient Chinese favored the black soybean. i
THE BENEFICIAL OR "PRO" SIDE
The most publicized contents of soy are phytoestrogens, especially isoflavones. Raw, mature soybeans contain about 0.2% isoflavones - genestein, daidzein, and glycitein. These compounds survive cooking. But not all soy products contain phytoestrogens. Different soy products contain different amounts of isoflavones. Some soy protein isolates are processed with an alcohol extraction that removes phytoestrogens.
Phytoestrogens are "believed" to behave as weak estrogen-like compounds in the body, and are thought to bind to estradiol receptors in tissues such as the uterus, breast, brain, bone, arteries, etc. Estrogen receptors on cells throughout the body are like locks to which only certain chemical "keys" can bind and open up activity. Phytoestrogens are thought to get into these "locks" and simulate estrogen function and/or block the uptake and effect of estrogens and other chemicals such as specific pesticides (xenoestrogens). The supposed pro- and antiestrogen effects of phytoestrogens are confusing and controversial. Scientists "speculate" that soy isoflavones, especially genistein and daidzein, may offer the benefits of estrogen for menopausal symptoms and protection of bone without the cancer risk attributed to estrogen. Genestein, for example, seems to have a greater affinity for the beta estrogen receptor than for the alpha receptor. Thus, it "may act differently" in different tissues depending on the nature of the estrogen receptors in that tissue. Theoretically, genestein could act as a pro-estrogen in the bones but an anti-estrogen in the breast. Researchers "suspect" that isoflavones in soy can prevent other cancers including ovarian cancer in women and prostate cancer in men.
In addition to the "unique and little understood properties" of isoflavones like genistein, there are still questions about the actions in living humans. In a test tube, genistein, in the absence of estrogens, has weak estrogenic effects and can stimulate cell growth, including breast cancer cells. Yet when a higher dose of genistein is added to the test tubes, the growth of breast cancer cells is inhibited. Does this happen in the breasts of living, breathing women? Not known. Other test tube (in vitro) tests show genistein as an inhibitor of tyrosine kinases, which "appear" to play a role in cell proliferation and transformation. Isoflavones inhibit the enzyme aromatase in test tubes, so "may" block one step in the conversion of testosterone to estrogen (estradiol). Isoflavones stimulate sex-hormone-binding globulin synthesis in the liver, so "may" reduce the biological effects of sex hormones including estrogen and testosterone. Is this good or bad or neither? Not known. Both daidzein and genistein inhibit free radicals in test tubes; genistein increases the activity of antioxidant enzymes such as glutathione peroxide, glutathione reductase, and superoxide dismutase. It is conjectured that "antioxidant effects" of isoflavones may protect against oxidation of LDL cholesterol, preventing atherosclerosis. Both test tube tests and animal or human (in vivo) studies seem to indicate phytoestrogens can act hormonally as both promoters and antagonists, competing with estradiol for estrogen receptors
Many reported positive effects of soy isoflavones have been extrapolated from test tube studies. Human studies "provide conflicting results" regarding the effects of isoflavone intake on estrogen levels including those in premenopausal women. Generally, high soy consumption "appears" to reduce estrogen levels in the plasma of premenopausal women. Changes may occur in the menstrual cycle such as an increase in the length of the follicular phase; delayed menstruation; suppression of midcycle surges of LH and FSH (reproductive hormones); decreases in estradiol, progesterone and DHEA, etc. Is this beneficial, detrimental, or neither? What form of soy was used? Could other variables in the lives of the women have produced these effects?
A human study with 10 young adult males who consumed a soy beverage for three weeks showed "increased plasma total antioxidant status values" [?] and a lower rise in plasma creatine kinase activity (an indicator of muscle tissue breakdown) than 10 men given a whey protein beverage. The soy maintained (the whey decreased) the post-exercise rise in uric acid (which "can be inversely proportional to oxidant activity" but also may not be). The study was sponsored by the Ohio Soybean Council, Protein Technologies, Inc. (which manufactures isolated soy protein), and the Gatorade Institute. It is no surprise that the trial had glowing results!
In some studies, soybean protein isolate seemed to prevent bone loss in animals whose ovaries were removed, but other studies showed no bone loss prevention. A clinical study of postmenopausal women showed increased bone mineral content and bone density in the lumbar spine, but not elsewhere. Another study found that soy prevented loss of spinal bone density. Researchers say that long-term, well-controlled studies are needed. A survey of animal studies was interpreted to indicate that soy isoflavones may retard bone loss almost as effectively as estrogen drugs, "at least in animals".
A study of 85 postmenopausal Japanese women who averaged 66.9 years of age - 60% with either osteopenia (bone loss) or osteoporosis - seemed to find benefit from soy protein. Soy protein intake was associated with an increase in lumbar bone mineral density and decrease in urinary deoxypyridinoline. Increased deoxypyridinoline (a marker of bone resorption) can be a sign of calcium loss from bone, while a decreased level may indicate reduced bone loss. The women had a protein intake of 62.5 grams per day, calcium intake of 733 milligrams a day, and soy protein intake of 12.6 grams a day. Why were benefits to bone attributed only to the soy protein?
Ipriflavone, a synthetic compound manufactured from daidzein, "holds great promise in the prevention and treatment of osteoporosis." But, "we have no studies on the effect of extracted isoflavones on bone at this time." This artificial isoflavone - at a dose of 600 milligrams a day -- did seem to promote an increase in bone density in one study. Since Ipriflavone is a drug, it could conceivably stimulate a temporary change in bone, but the beneficial effects attributed to it would wane and possibly backfire. A recent study showed that after 36 months of treatment with Ipriflavone, there was no difference in bone mineral density, fractures did not lessen, and over 13% of the women receiving Ipriflavone developed abnormally low lymphocyte (white blood cell) counts
Clinical studies on soy and cancer show mixed results. Increased isoflavone consumption resulted in decreased urinary excretion of various and total estrogens and "hypothesized genotoxic estrogen metabolites." Thus it was proposed that soy isoflavone consumption "may exert cancer preventive effects by decreasing estrogen synthesis" and shifting metabolism away from genetically-toxic products towards inactive metabolites. Quite a presumptive leap! Could not the reduced estrogen secretion also be interpreted as something detrimental? Is estrogen a toxin or, as shown many years ago, is the connection of estrogen to breast cancer really due to the fact that the liver is not healthy enough to properly convert estrogens into beneficial and useful forms? Did Nature goof or are humans creating hormonal aberrations by chemical poisons and eating nonfoods, then interpreting Nature's ways as harmful?
Studies in humans "raise questions" about proliferative - thus cancer-promoting - effects caused by soy intake. Epidemiological (cause, incidence, and behavior of disease) information "suggests" that soy intake protects against breast cancer. Women given soy supplements such as soy protein isolate experienced significant increases in the proliferation rate of breast epithelium tissue, increased secretion of breast fluid, elevated levels of plasma estradiol, etc. Human studies causing concern about breast cancer were associated with products containing concentrated and isolated soy isoflavones including soy powder, soy beverages, and isolated genistein - not soy foods such as tofu or tempeh. Studies among Asian women and men "suggest" that soy intake may protect against breast cancer, prostate cancer, and colon cancer, but there is "insufficient data" to determine how much soy must be consumed or whether it is soy at all that offers the protection. Are the reduced risks due to other lifestyle habits including a diet high in fruits and vegetables and generally low in pesticide, hormone and drug residues? "Doubts as to the significance of the breast cancer protective effects of soy and the safety of soy in breast cancer patients will remain."
Soy supplementation in women has resulted in "significant improvements" in cholesterol levels, blood pressure, and "perceived severity of vasomotor symptoms" like hot flushes. Studies have shown increased serum growth hormone and prolactin, decreased levels of LH and/or FSH (pituitary hormones that increase with menopause), and increased vaginal maturation (an indicator of estrogen effects). Other studies do not show such changes. In one study, a 400- milligram standardized soy extract (yielding 50 mg daily of isoflavones) was given to women for six weeks, resulting in a reduction in hot flushes of about 45% versus 25% for the placebo group. The standardized soy extract did not change any cholesterol numbers. Another study using either 50 mg of soy isoflavone extract or placebo over 12 weeks showed "a significant change" in both the number and severity of hot flushes in both the soy group and the placebo group, and a very slight reduction in hot flush severity in the soy group over the placebo group. There was a 28% reduction in hot flush severity in the soy group and a 20% reduction in the placebo group. The number of hot flushes were about the same for both groups. No changes were seen in cholesterol levels or bone biochemical markers. Apparently, psychological factors exert a strong influence on hot flushes.
Some studies suggest soy isoflavones may help lower serum cholesterol. Isolated isoflavones and isolated soy protein may lower total and LDL (so-called "bad) cholesterol without affecting the triglycerides or HDL (so-called "good") cholesterol in people with mildly elevated cholesterol levels. Of course, the definition of high cholesterol and the "badness" of LDL are still controversial. A recent study on postmenopausal women with mild elevations of cholesterol used isolated soy protein (ISP) and found only "small but significant" improvements - 6.5% lower LDL; 8.5% to 7.7% lower ratio of LDL to HDL cholesterol. A trial of 20 people with type II diabetes compared the effects of a soy-based dietary supplement, Abalon, with a control supplement. LDL cholesterol, LDL/HDL ratio, apolipoprotein B100, triglycerides, and homocysteine levels were all lower in the soy supplemented group. A 1995 meta-analysis concluded that consumption of 25 to 50 grams of soy protein, compared with animal protein, resulted in decreased LDL concentrations by 7% to 24%, depending on the initial total cholesterol concentrations. Whether the effect was due to the soy protein or to other factors is yet to be determined. Since then, studies have reexamined the effect of soy protein and isoflavones on blood cholesterol and triglyceride concentrations. "The results of more recent studies are variable." The effects seem to depend on whether the isoflavones are ingested in isolation or added to soy foods. Isolated isoflavones given in pill form have no significant effects on blood lipid concentrations. Soy foods have beneficial effects, though if isoflavones or other components are removed, improvements are not as significant. A meta-analysis of 38 controlled trials on women and men showed about a 10% reduction in total cholesterol, 12% reduction in LDL, 2% increase in HDL, and 10% reduction in triglycerides. Overall, the effects of soy protein on blood fats are "inconsistent."
In one study, researchers fed men with mildly elevated cholesterol a low fat diet containing muffins with 25 grams of protein and 20 grams of fiber. Each of four groups received different muffin additions: soy protein and soybean fiber, soy protein and cellulose; casein and soybean fiber; or casein and cellulose. At the end of the study, the two groups fed casein-containing muffins did not have significant changes in cholesterol. The two groups fed isolated soy protein had "significantly lowered total cholesterol." The soy protein was an isolated concentrate, not really a food. Soy extracts seem to reduce coronary artery atherosclerosis and dilate coronary arteries in monkeys.
A study looked at cholesterol levels in men fed diets supplemented with either animal (meat/ dairy) or soy protein. LDL cholesterol decreased by 6% and the LDL/HDL ratio fell by 11% in the men receiving the soy supplement. The study was not even single-blinded, and the specific foods and meals used were not described beyond mentioning the use of soy beverages and meat substitutes. The men started the study with normal cholesterol levels. Were the LDL decreases desirable? Were they temporary reactions or compensations?
The FDA concluded that foods with at least 6.25 grams (about a fifth of an ounce) of soy protein per serving qualify for a health-claim label saying they may help reduce the risk of heart disease, as long as they are consumed as part of a diet low in saturated fat and cholesterol. As Neal Barnard of the Physicians Committee for Responsible Medicine explained, adding a bit of tofu to a typical American diet "does virtually nothing." People would have to incorporate soy and other legumes into "a low-fat, pure vegetarian diet" to enjoy the fullest benefits. Although soy protein, when substituted for animal protein in the diet, lowers blood cholesterol, no one knows why. Researchers still disagree about whether it is the protein or something else in soy that lowers cholesterol. There is no evidence that isolated soy isoflavones reduce cholesterol. Some scientists are convinced that isoflavones have little if anything to do with cholesterol reductions. They show evidence that genistein may even raise cholesterol. Other components of soy protein - not isoflavones - may be more likely responsible for lowering cholesterol. In early studies and most European studies, the soy products given to people with elevated cholesterol levels were essentially free of phytoestrogens.
The hypothesis of cardiovascular benefits coming from lowering LDL and raising HDL is "dubious." Some researchers have concluded that serum levels of LDL and HDL are not good risk predictors for cardiovascular disease. Some research indicates that high levels of HDL occur with thyroid problems. Soy has been implicated for antithyroid effects, causing reactions on many areas and functions of the body. Elevated levels of a substance called lipoprotein(a) has been shown to be an accurate marker for heart disease proneness. And soy has been shown to raise levels of lipoprotein(a).
Frequent consumption of soy milk was associated with a reduced risk for prostate cancer. Isoflavones "may" be one of the protective factors. What of other dietary components or lifestyle differences? In test tubes, soy isoflavones, particularly genistein, seem to inhibit prostate cancer cell growth. But studies with metamorphosised cell lines in laboratory petri dishes where clumping or non-clumping of cells is interpreted as cancer-causing or cancer preventive are a far cry from actual clinical experiences with real, live, complex humans. A recent study of 34 elderly men supplemented with a soy protein beverage containing either high or low doses of genistein and daidzein showed no affect on serum prostate specific antigen levels, a test used to indicate prostate cancer tendency.
Phytoestrogens in soy are thought to help maintain brain function. Early studies at Wake Forest University seemed to indicate that soy exerts positive effects on memory, influencing nerve cells in a similar way to estrogen. In Japan, rates of dementia, including Alzheimer's disease, are slightly lower than those in the U.S. Can this be attributed to soy consumption or is it due to any number of other factors?
Much of the adverse data on soy comes from studies using isolated isoflavones, not whole soy. Whole foods do not work in the body the same way that isolated compounds, drugs, or "bioidentical" hormones do. "Plant foods, with their exquisite combinations of interactive ingredients, work to balance the body on a number of levels simultaneously," explains Dr. Christiane Northrup. For example, various plants and herbs used for menopausal symptoms - such as flaxseed, legumes, dong quai, chasteberry, black cohosh, red clover, etc. -- "will act in slightly different ways," and with various degrees of effectiveness for different individuals, "but they all help balance the endocrine system." So far, "conflicting studies have muddied the waters in terms of understanding exactly how soy affects the body." Foods and humans are complex with too many variables. ii
DETRIMENTAL OR "CON" SIDE
Phytoestrogens are nonsteroidal plant compounds that bind with human (or animal) estrogen receptors, says Claude L. Hughes, Jr., M.D., Ph.D., of Cedars-Sinai Medical Center in Los Angeles, "sometimes stimulating estrogen responsive behaviors, sometimes blocking them." More than 300 plants including some legumes, grains, seeds, and herbs, are "known" to have "estrogenic activity", including soy. Phytoestrogens (genistein and daidzen) in soy can be converted by intestinal flora to "the far more potent isoflavone] equol," which is absorbed along with unconverted genistein and daidzen. "Although most phytoestrogens are relatively weak" compared with human or animal steroid hormones, occurrences (such as infertility) in large animal trials "dramatically illustrate their potential for potent biologic effects when ingested regularly in large quantities." What of species specificity? Can results of animal studies, particularly with isolated compounds, be applied to humans? Dr. Hughes is fascinated by the "spectrum of thousands of diverse chemicals in our diets." Phytochemicals may affect us, "yet we barely understand anything about most of them!" This stresses the need to consider whole foods containing all their bioactive synergistic complexes rather than separated parts.
"The extensive and long-term ingestion of soy is the biggest human experiment that is under way", asserts Dr. Hughes, "yet no one, until recently, has been asking what these dietary hormones are doing to us, or collecting data on their health impact." Although often used interchangeably, there is a need to separate the concepts of soy food and soy components. Isolated compounds, like protein isolates, oil, phytoestrogens, etc., may have extremely different effects than whole (properly prepared) soy food. "We have to treat phytoestrogens as dietary pharmaceuticals" since these chemicals are studied as isolates and used as drugs. Also, the "framework within which most of us view the use of soy products - and thus their phytoestrogen content - is based as much on myth as on reality." No magic remedy, while some adverse side effects have been reported.
For instance, soy is "far from the menopausal panacea that we see touted in much of the consumer literature." Many major menopausal symptoms and problems are "untouched by soy estrogens." These include atrophic vaginitis, unstable bladder, atrophy of the lower genital tract tissue, etc. If soy had the benefits of estrogen, these and other problems would improve or be less severe or not appear. Some endorsements of soy phytoestrogens for menopause - often touted as nature's answer to Premarin, providing hormonal benefits without discomfort, monthly bleeding, or increased cancer risk - are "largely uninformed," based primarily on circumstantial observations that Asian women have lower rates of uterine and breast cancer compared with Western women. Yet Asian women have a high incidence of osteoporosis. Attributing one estrogen effect to soy but not the other is inconsistent. Claiming that phytoestrogens are crucial in raising menopausal age and lowering breast cancer risk in Oriental women "is superficial." By the same token, one could say that soy might account for the increased rate of gastrointestinal cancers seen in Asian peoples. "To single out putative [supposed] beneficial or harmful roles of nutrients within the complex array of dietary and life habits, culture, and genetics seems somewhat imprudent."
Menopausal symptoms are highly subjective, studies showing that controls taking placebos have as much relief as those taking soy products. The candid Dr. William Campbell Douglass queried: "If Asian women have fewer menopausal symptoms, why are there so many Chinese herbs for the relief of hot flashes?" Soybeans and soy milk products have had no effect on the bones of experimental animals. Most research on isoflavones suggests that they do not exert estrogenic-like effects on the uterus and endometrial (uterine lining) tissue.
Seven studies that compared soy protein shakes, bars, muffins, and flour to look-alike (but soy-less) placebos had inconsistent results. Two studies found that soy eased hot flushes. Both studies used similar soy powders, but their results were inconsistent. In one, drinking soy once a day did nothing to relieve symptoms, while taking it twice a day reduced the severity, but not the number, of hot flushes by 20%. In the other study, the average number of hot flushes in the soy-drinkers decreased from 11 a day to six. In the placebo group, it dropped from 11 to eight. That is "a very modest difference." Severity of hot flushes was not measured. Another study had three groups receiving 80 mg of soy isoflavones, soy protein excluding isoflavones, or whey protein as the control. From beginning to week 12 there was a decline in the frequency of hot flushes in both soy groups, but then there was an increase in hot flushes from weeks 12 to 23 in the soy-protein excluding- isoflavones group, with little change in the soy isoflavone group or control group. The soy-isoflavone treatment "had no appreciable effect on hot flushes or night sweats." Soy has not been shown to have any beneficial effect on symptoms like anxiety, mood swings, fatigue, libido, vaginal dryness, urinary frequency, headaches, or insomnia. In five other studies, soy products were no better than soy-free placebos at relieving any menopausal symptoms. "Most studies find that soy has no effect on menopausal symptoms," says Gregory Burke at Wake Forest University. When a benefit is detected, it is relatively mild.
There has not really been any good published data indicating that supplements (such as those containing isoflavones) have a significant impact on menopausal symptoms like hot flushes or night sweats. Further, large doses of isoflavones (from powders or pills) "may not be safe." Supplement companies promise dramatic results for relief of menopausal symptoms. However, for most symptoms like hot flushes, "the placebo effect is giant," as one manufacturer admitted.
There is no evidence that soy helps PMS (premenstrual syndrome). Some women actually report adverse effects such as painfully swollen breasts, increased bloating, cramping with menses, and migraine headaches. Soy phytoestrogens increase division of breast cancer cells in culture (petri dishes). But "we just don't know the reality in vivo [in living humans] yet." Overall, there are "inconsistent data" regarding any hormonal effects of soy on breast tissue of either pre- or postmenopausal women. An epidemiological study in China indicated that high soy intake is not protective against breast cancer.
Whether attributed with lowering risk for breast cancer, colon cancer, or any other cancer, soy has not been conclusively shown to be a protection or cure. Most studies have been performed in test tubes. "Exactly what type of cell proliferation represents a risk for carcinogenesis [cancer production], and what type of inhibition of cell proliferation will therefore be protective against cancer?" The uncertainties are numerous and application to humans is guesswork at best. An exhaustive study by the British government in 1997 led the researchers to conclude that there is "no evidence that soy products inhibit cancer anywhere other than in test tubes."
Researchers at the Mayo Clinic concluded that it is too soon to conclude that soy isoflavones can be an effective alternative to estrogen treatment. After examining a number of studies on the effects of isoflavones on coronary artery disease, bone loss, cancer prevention, the central nervous system, skin, endometrium (uterine lining), and reduction of hot flushes, they reported that it would be "premature" to consider taking isoflavones instead of estrogen.
Even if plant compounds can play the role of hormone mimics, they are certainly not natural human hormones. While many plants, including herbs, have been and are being used to aid hormonal imbalances or deficits, they perform as hormone precursors or as biochemical balancers, not as human hormones.
Some people fed soy baby foods later develop severe autoimmune diseases, reproductive dysfunctions and/or "compromised" sexual identities. One study found that a high-soy diet during pregnancy and breast-feeding affected the development of sex characteristics in baby rats. Cases are reported of women who were fed soy baby foods growing up to be infertile or have babies with birth defects. Soy has been attributed with contributing to osteoporosis.
In the 1986 Puerto Rico Premature Thelarche study, the most significant dietary association with premature sexual development was soy infant formula. The second most powerful association was chicken - raised on soy-based feed. Approximately 25% of bottle-fed babies in the U.S. receive soy-based formula. Researchers reported in 1998 that the daily exposure of babies to isoflavones in soy infant formula is six to 11 times higher on a body-weight basis than the dose that has ‘hormonal' effects in adults consuming soy foods. Anecdotal reports of other problems for children who were fed soy-based formula include asthma, disturbances in the immune system, extreme emotional behavior, pituitary insufficiency, thyroid disorders, and irritable bowel syndrome. Effects of isolated isoflavones on various experimental animal species include hormonal changes, increased uterine weight, and infertility. K.O. Klein of DuPont Hospital for Children stated: "It is clear from the literature that different species and different tissues are affected by isoflavones in markedly different ways. It is difficult to know which tissues, if any, are affected in infants, and the variation among species makes extrapolation to infants inappropriate." Nevertheless, findings from animal studies may give reason for pause.
For example, in one study mice were given breast-cancer-inducing chemicals followed by either food pellets fortified with genistein or genistein-free pellets. Of 11 mice fed genistein, 5 developed breast tumors; none of the mice in the control group developed tumors. In a study of uterine cancer, three groups of newborn mice were injected with genistein and corn oil, or the synthetic estrogen diethylstilbestrol (DES) which is known to cause cancer, or corn oil alone. At 18 months of age, none of the control mice had developed cancer, 4 of 13 DES-treated mice developed cancer, and 6 of 17 genistein-treated mice developed cancer. One of the study's authors said that the amount of genistein administered to the mice was only slightly higher proportionally than the amount human infants on soy formula would ingest. Other scientists argue that millions of infants have been given soy formula since the mid-1960s with no signs of increased risk for cancer. Yet, hormone disruptions are evident including a drop in the age of puberty among girls, an increase in testicular cancer in young men, and decreased sperm counts. There are many possible reasons for these aberrations - from pesticide exposure and increased consumption of altered fats to nutritional deficiencies and hormone residues in meat products. But could soy be another culprit?
According to a study in Journal of the American Medical Association, babies fed soy-based infant formula are just as healthy and grow up to have equally healthy infants later in life, compared to those fed milk-based formulas. No comparison was made to babies who were breastfed. The study's authors did find a "somewhat" longer monthly menstruation length and greater discomfort in women fed soy formula as babies, but this was dismissed as only "slightly significant." Jan Kallio of Massachusetts WIC said that breastfeeding is the best way to feed infants, but if a mother decides not to breastfeed or has a problem breastfeeding, a cow's milk formula is recommended. Soy formula is recommended only if a child has a feeding problem such as allergies (to milk) or a metabolic disorder. The JAMA study was funded by the Infant Formula Council with grants to the chief researcher coming from Ross Products Division, Nestle, and Mead Johnson Nutritionals - all with financial interests in soy-based infant formulas.
New Zealand's Ministry of Health research showed that infants fed solely a soy-formula are exposed to 16 times more isoflavones than is necessary to cause goiter in adults. Soy has been associated with thyroid disruptions for many years. The danger for infants is especially great if soy formula is given for longer than three months. In a study reported in 1998, Daniel Sheehan of FDA's National Center for Toxicological Research stated: "Among human exposures, infant soy formula exposure appears to provide the highest of all phytoestrogen doses, and this occurs during development, often the most sensitive life-stage for induction of toxicity. Large, carefully controlled studies in this exposed infant population are a high priority." The use of soy infant formula in the U.S. almost doubled during the 1990s to a total of 25% of the market. The American Association of Pediatrics claims that soy formula is "a safe and effective alternative to provide appropriate nutrition and normal growth for term infants." But it does not recommend soy formula for premature infants with low birth weights due to concerns with failure to achieve normal growth rates and aluminum toxicity. Manganese levels in soy beverages are over 50 times the level found in mothers' breast milk. Some scientists are concerned that this may be neurotoxic to infants under six months of age. High manganese amounts could imbalance other trace minerals such as zinc and chromium.
Daniel Sheehan, Ph.D., of the National Center for Toxicological Research wrote that some isoflavones, including genistein and equol, are toxicants. He believes infants fed soy formulas have been placed at risk in a "large, uncontrolled, and basically unmonitored human infant experiment." Dr. Mike Fitzpatrick, a biochemist and former Auckland University professor, feels that soy may combine with other xenoestrogens (such as pesticides). "Because of the potential for synergistic effects, human exposure to all endocrine disrupters, such as the soy isoflavones urgently requires reduction."
Dr. Sheehan stresses that isoflavones are inhibitors of thyroid peroxidase which makes T3 and T4. Inhibition "can be expected" to generate thyroid problems such as goiter and autoimmune thyroiditis. Infants consuming soy formula with its isoflavones "have about a two-fold risk of developing these diseases." He thinks isoflavones are like "other estrogens" and confer both benefits and risks. Ingestion of soy protein has been reported to cause goiter and hypothyroidism in clinical studies and animal studies. The study with infants suggested that ingestion of soy formula reduces intestinal absorption of L-thyroxine. "If these results can be extended to other soy products and to adults, then people taking thyroid hormone should not consume soy products at the same time."
Soybeans have long been considered goitrogenic (causing thyroid enlargement) in humans and animals. Rats fed an iodine-deficient diet containing 40% defatted soybean developed thyroid cancer. One investigator showed that the "anti-thyroid" activity in acidic acetone soybean extracts is water soluble, is diffusible, and is not removed by either ammonium sulfate or trichloroacetic acid (used in soybean refining processes). The "active ingredient" was not destroyed by either digestion with pancreatin or by boiling for two hours." This was a test tube study. Isolating the toxic "active ingredient" may be just as inconclusive and confounding as efforts to isolate a beneficial "active ingredient" in foods. Some experts believe that only certain people are more prone to hypothyroidism from eating soy. "For soy to actually cause hypothyroidism, you'd have to be bordering on hypothyroidism to begin with," says Martin Milner, N.D., Center for Natural Medicine in Portland. Also, the amount and form of soy consumed can determine whether it interferes with thyroid function, according to Daniel R. Doerge, Ph.D., National Center for Toxicological Research. Anecdotal reports indicate that persons with mild hypothyroidism or tendencies toward hypothyroidism will be more likely to have thyroid problems by eating soy. Women going through puberty, pregnancy, perimenopause, or menopause - times when there are changes and stresses on the thyroid - may experience some thyroid disruptions.
Replacing 90 grams of meat protein with 90 grams of soy protein (about four blocks of tofu) a day lowers testosterone - male hormone - by about 10% relative to the level of estrogen. This would not make men happy! It is thought that "too high a level" of isoflavones can raise estrogen and lower testosterone. But is it also possible that reducing the intake of meat would contribute to this effect? iii
Soy is a very complex food. Reviewing the pros and cons, there appears to be cause for confusion, leaving more questions than answers. Soy seems to lower cholesterol levels. Its other effects, whether seen as good or bad, are related to the hormonal changes attributed to it. The soy industry promotes soy products as estrogen substitutes for menopausal women, yet they sell infant formulas and claim there is no important estrogen effect. Some studies conclude that soy prevents cancer; others indicate it causes cancer. Is soy beneficial or detrimental to human health? Is there any clarity to be found in this muddy issue? Part II of this article may help.
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Originally published as an issue of Nutrition News and Views, reproduced with permission by the author, Judith A. DeCava, CNC, LNC