What Are Phytoestrogens?
Phytoestrogens, which include lignans and isoflavones (e.g. genistein and daidzein), are oestrogen-like compounds which occur naturally in many plants and fungi and which are biologically active in humans and animals. Soya, particularly tofu and miso, other pulses, citrus fruits, wheat, licorice, alfalfa, fennel and celery are rich sources of phytoestogens in the human diet.
Recent Concerns About Phytoestrogens & Soya Baby Milks
Recent research from New Zealand(1) raises concerns about the potential adverse effects of phytoestrogens in soya baby milks. This has been widely reported in the media in this country. The 1994 report from New Zealand examines the toxicity of soya and questions the suitability of feeding babies soya-based infant formulas. The report was co-authored by New Zealand aviculturists Richard and Valerie James, among others, who became mystified by the range of health problems their breeding parrots - some 600 birds of 40 species - were developing, including infertility, reproductive disorders, premature maturity and death caused by immune system failure. Confering with other experienced aviculturists and animal breeders in New Zealand, Australia and the US, they discovered widespread breeding, growth and behavioural problems and deaths in finches, rabbits, poultry, guinea pigs, cats and fish. Analyses of commercial bird feed and other animal feed indicated that soya ingredients were associated with the toxic effects. They then became concerned about the effects on infants fed a soya-milk formula. From analyses of levels of isoflavones (soya phytoestrogens) in soya-based infant formulas available in New Zealand, the researchers calculated that the biological effects of phytoestrogens typically consumed by a baby drinking soya milk would be 100 times greater than the amount of natural oestrogen the child would receive from breast milk. Their research prompted the New Zealand government to undertake a review of soya-based products for human consumption and to take the issue up with the World Health Organisation.
Other Research
Growing evidence indicates phytoestrogens may reduce the risk of certain cancers, especially those which are hormone dependent such as breast and prostate. Epidemiological studies have shown that Japanese women have a lower incidence of breast cancer than women consuming a typical Western diet. Likewise, Japanese men have a lower incidence of prostate cancer. In addition to this, certain phytoestrogens, notably genistein, may also protect against cardiovascular disease by inhibiting platelet aggregation and reducing serum cholesterol levels(2).
Daily intakes of 45mg of phytoestrogens have been shown to have beneficial stabilising effects on hormone balance. Women in the Far East ingest between 150-200mg of phytoestrogens a day. Dr Herman Adlercrutz and colleagues from the University of Helsinki, studied residents of a rural village near Kyoto who still eat the traditional Japanese diet. They found that those who ate the most soya bean foods had the highest content of phytoestrogens in their urine. Typically the women ate 3oz of soya bean products a day, including tofu, miso, fermented soya beans and boiled soya beans.
However, evidence also indicates that their action in the human body is complex, and that exposure to endogenous oestrogens, including phytoestrogens in the womb and during early childhood, may pose risks to sexual development. US researcher Claude Hughes and colleagues conclude that exposure to phytoestrogens in the womb and during childhood "could easily exceed the narrow bounds of optimal or physiologic levels and thus be of significant toxicologic concern."(3)
Amounts of Phytoestrogens in Soya
The Food Commission asked companies supplying soya baby milks in the UK to provide information on levels of phytoestrogens. Wyeth (which makes SMA Wysoy - not a completely vegan formula) states that: "Our soy formula contains no more than 20-28µcg/ml (of phytoestrogens) in the reconstituted product". This appears to be approximately two-thirds of the levels found in New Zealand formulas. The baby milk companies' trade association, the Infant & Dietetics Food Association, was unable to supply them with any figures for the UK products. However a spokeswoman did suggest that all products would contain broadly similar amounts as she thought that companies "all bought soya from the same supplier". She added that levels could fluctuate according to seasonal and other environmental factors.
The amount of phytoestrogens consumed depends on the foods eaten. Genetic variation between soya cultivars and processing may influence phytoestrogen content. Researchers from Boston and Helsinki analysed several soya products available in the US, including four brands of tofu, a soya drink, and soya-based liquid formulas used as dietary supplements for adults. Duplicates were analysed by an isotope dilution gas chromatogrophy-mass spectrometry method. Tofu products were found to be highest in isoflavone content, containing significant levels of genistein and daidzein. The soya drink had about a tenth of the amounts of genisten and daidzein found in tofu. The soya-based formulas were almost devoid of these two isoflavones.
Exposure To Phytoestrogens From Other Sources
Environmental Chemical Pollutants
At least 37 chemicals have been identified as being able to either mimic oestrogens in the body or to interfere with the various systems that regulate the body's production of oestrogen and other sex-linked hormones. These include the chlorinated hydrocarbon, DDT, its breakdown product (DDE), some polychlorinated biphenyls (PCBs), dioxins, several pesticides and fungicides, and some chemicals used in detergents and plastics.
Many of these substances do not biodegrade and are widely distributed in the environment - the food chain, water supply, etc and accumulate in fat tissues in animals and humans. They can cross the placenta to the developing fetus. There is no conclusive evidence that these exogenous oestrogens affect human development. Wildlife and laboratory animal studies indicate that many of these chemicals are detrimental to reproductive development.
From 1940 onwards the use of chemicals began on a large scale. The first generation of people exposed as fetuses or young infants to chemicals which act like, or mimic oestrogen, began reaching their reproductive ages in the 1970s. Dr Richard Sharpe of the Medical Research Council points out that because some consequences of this exposure may not become manifest for some 20 to 40 years after birth, the extent to which children born today might be affected may not be clear until well into the next century.
Synthetic oestrogen (ethinyl oestradiol) is used in many formulations of the contraceptive pill. It has contaminated water supplies but does not appear to be present in significant concentrations. In fact environmental pollutants seem to be a far greater source of exogenous oestrogens. Another synthetic oestrogen, diethylstilbestrol (DES), was widely used as a growth promoter in cattle and other livestock from the 1950s until the early 1980s, when it was banned. From 1948-1971, DES was also prescribed to over 5 million women diagnosed as having low levels of oestrogen, mainly in the US but also in the UK. Daughters of women who were given DES have a higher risk of developing rare vaginal cancers, while sons have an increased risk of abnormally-small testes, malformed penises, testicular cancer, low semen volume and low sperm counts. Today, endocrinologists regard the effect of DES on human offspring as a model for the problems that other oestrogen-like substances may cause.
Current Thinking & Recommendations
Donald Shutt, a former consultant to the World Health Organization on phytoestrogens, has stated that more research is urgently needed to assess the potential oestroenicity of soya formulas for infants. One problem, however, is that it is neither easy nor ethical to study the effects of phytoestrogens on babies.
Dr Richard Sharpe of the Medical Research Council's Reproductive Biology Unit in Edinburgh recommends caution. "We just don't know enough about the effects of oestrogen-type chemicals on the developing foetus and new born babies. Therefore I would recommend that exposure to oestrogens from whatever source should be kept to a minimum especially during childhood".
In 1992 the UK government's expert Committee on Toxicity(4) recommended that levels of phytoestrogens in soya baby milks and other soya foods for children should be analysed as part of its review of natural toxicants in foods. The Ministry of Agriculture, Fisheries & Food told the Food Commission: "It is on our priority list and we hope the work will start in 1995. We are keeping an open mind and a close watch on this, though we are not aware of any reports of adverse effects".
New Zealand researchers and The Food Commission in the UK are recommending that soya baby milks should be withdrawn from general sale until further research has been carried out.The Food Commission is backing advice by New Zealand researchers and the US Food & Drug Administration Dept of Health to stop sales of soya infant formula milks until definitive epidemiological research has been completed. Soya formula milks would still be available on prescription on medical advice from a doctor. The Food Commission also recommends: Breast feeding as a first choice For bottle feeding, the Department of Health (5) recommends that soya formula milks should not be a first choice unless there is a specific reason for excluding cow's milk form the diet.
Berrydale News (1.6.95), England, reports that: "no-one has mentioned that this New Zealand research had been commissed privately by two new Zealanders concerned about the side effects on their pet parrots - not their babies - of eating soya ... Secondly, the research had not been published and so had not been peer reviewed. Indeed the report was only available on payment of a substantial fee. Thirdly, both the limited published data which does exist on phytoestrogens, and the comparative data on the oestrogenic activity of breast milk, was ignored. And fourthly, both the New Zealand government and their national association of health visitors, having read the report, stated that there was insufficient evidence to warrant any action".
Dr David Ryde, former GP from England, writes on the subject "Whilst I appreciate the Food Commission's reasons for calling for the withdrawal of soya infant formula milks due to the possible detrimental effects of the phytoestrogens in soya, an interesting question arises: What happens to Chinese or Japanese children who consume relatively large amounts of soya? Some oriental adults consume 55-60g soya protein daily.
Oriental girls commence menstruation aged roughly 16-17 years and have a cycle of about 30 days, while their western sisters start at about 12-13 years and have a 28 day cycle. (Do they start late or do we start early?) Do young oriental girls have menstrual problems or become infertile? I doubt it. Indeed, menopausal women out there have a very mild 'change' compared with western women.
Phyto- or plant oestrogens (present in some peas and beans) are very weak compared with body oestrogens and compete with the body oestrogens for the oestrogen receptors, and so, in effect, reduce oestrogen activity. By having a lower body oestrogen profile Japanese women at menopause have a reduced 'hormone dip' and hence fewer and milder symptoms.
Since breast and prostate cancers are hormone dependent, it is not surprising that the incidences of such diseases (including osteoporosis) is reduced in oriental people. Another factor is the low fat content of a plant-based diet, since visceral (inner fat) also produces oestrogens and most people on a plant-based diet are sually slim."
Dr Michael Klaper MD is an honors graduate of the University of Illinois in Chicago and has postgraduate training in medicine, surgery, anesthesiology and obstetrics. His clinical experience includes eight years of conventional general practice, and three years as physician in an isolated hospital in the mountains of northern California. He says regarding the issue of soy formula and infants, the questions raised are legitimate, but "I feel the concerns may be a bit overblown, for the following reasons:
1. It is true that soy formula contains isoflavones, a family of molecules made by the soy plant that can exert weak estrogenic activity in humans. However, in adults, these isoflavones have a rather remarkable effect of not increasing estrogenic activity, as one might think, but actually normalizing estrogen levels. That is, most women who eat the standard Western high-fat diets walk around with high levels of estrogens in their bloodstream, which seems to increase their risk for breast cancer. The isoflavones will occupy the receptor sites on the surface of breast tissue cells to prevent the woman's own potent, fat-induced, estrogens from exerting their effects of promoting cell division, and thus isoflavones can actually protect the woman from possible development of breast malignancy. That is, soy-derived isoflavones will lower the estrogen level of a woman whose estrogens are obnormally high and apparently reduce her risk of breast cancer.
On the other hand, women who are on very low-fat diets, like anorexic women or marathon runners, or strict ethical vegans with insufficient nutritional knowledge (and this a diet deficient in essential fats), may all have abnormally low levels of estrogen in their blood. This poses a danger to their reproductive functioning, bone health, and probably other organ systems. In these women, the addition of tofu, tempeh, soy milk, and other soy-derived products contributes isoflavones which exert their estrogenic effect and will raise the hormone levels of these women, bestowing beneficial effects upon them. Thus, soy products have remarkable normalizing properties regarding the estrogenic effects of isoflavones. The issue is what effect these substances may have when consumed by newborn infants. It is difficult to say, for many reasons. The physiology of a newborn is very different than that of an adult and we really have not studied the subject hardly at all. By that I mean, no one has investigated what happens inside the newborns physiology from these soy-based isoflavones in any significant way. It may well be that the newborn's liver removes all the isoflavones out of the bloodstream in the first pass or two of the blood through the liver, so perhaps there's no effect at all. Or, maybe the newborn's cells are insensitive to the isoflavones - I can't say I remember an increased incidence reported of breast enlargement or feminization of infant boys drinking commercially-produced soy milk. But maybe these effects were never looked for ...
Before all sorts of scowls are raised over the levels of these phytoestrogens, especially when compared to oral contraceptive tablets, realize that no one has any serious idea of what effects actually may be. When considering alternatives to human mother's breast milk, the choices are always a poor compromise:
1. Either one leaves the animal kingdom altogether and actually constructs a soy "milk" utilizing all plant derived materials - substances chemically foreign to the human body, but apparently well tolerated and supportive of growth (as a generation of babies have already grown and thrived while nursing on soy formulas), or 1. One resorts to the milk of another mammal, and in our society, this is the lactation secretions of bovines. By instituting cow's milk-based infant formula, one accepts the fact that the baby's highly-absorptive intestine will be smeared with proteins very much like human proteins - forms of albumin, globulin, etc. that can enter the baby's bloodstream and engender significant reactions: a) Fragments of milk proteins can incite a vicious, brittle, juvenile diabetes when absorbed into the bloodstream by invoking antibodies that cross react against the surface proteins of the pancreas cells that make insulin. b) Casein and other proteins are implicated in childhood asthma, eczema, and gastrointestinal bleeding. c) Exacerbation of enteritis and colitis induced by dairy consumption in lactose-deficient individuals. d) Exacertbation of rheumatoid arthritis in dairy-sensitive patients, etc.
Those who would indict soy-based formulas are also overlooking the fact that cow's milk itself is loaded with estrogens. Remember, the mother cow in the dairy has recently given birth and she is still in a high estrogen state. Her milk is laced with estrogens-not mildly active, plant-derived phytogensactive, but highly active mammalian estrogens, and they may have some significant effects, like precocious puberty, that have not been fully recognized.
I hope I haven't muddied the water too much but one must be able to parry some of the implications of the question being raised. I think, before this gets too hysterical, we should always compare with real-life experience. Soy milks were introduced over twenty years ago, and, as I said, there is an entire generation of young adults who started their lives and obtained most of their energy, protein and vitamins from soy-based formulas during the first one to two years of their lives. If there is serious concern about the issue, these young people, now in their twenties, should be identified and surveyed for intellectual development, sexual development, etc. If they have no higher incidents of abnormalities in these areas than children raised on cow's milk formula, then I feel that there is probably little cause for concern.
All this points to the fact that human breastfeeding is by far the preferable form of nourishment for human infants. Most women can breastfeed if they choose to (though some may require coaching by an experienced lactation consultant) and I feel encouragement of breastfeeding should be a prominent message from vegan organizations.
Considering the balance of all the above (and in view of our admittedly limited understanding at this point in time), I believe one can make the legitimate case for soy-derived formulas being the preferable breastfeeding alternative over infant formulas made from cow's milk."
Mark Messina MS PhD, author of The Simple Soybean, says "My wife and I, who are long time vegans, recently co-authored a book called The Simple Soybean and Your Health. I am very familiar with the issues being raised in New Zealand, and in fact, I debated Dr. Clifford Irvine, who was quoted in the article Living Earth and The Food Magazine April-June 1995.
There is a lot of hysteria being generated about soyfood toxicity. Much of it based on a report that was cited in the article; it was written by a single individual and is extremely flawed and biased. A Mr James of New Zealand , has made it has personal mission to see that soyfoods, particularly infant soy formula, carry warning labels. Also, two of the major participants in this soy controversy in New Zealand are consultants to the dairy industry. However, I don't like to ascribe motives to people unless I have first hand knowledge, which I don't. It's best to focus entirely on the scientific issues involved. Furthermore, some legitimate scientists are expressing honest concerns about soy.
Most of the hysteria is due to the presence of compounds in soybeans called isoflavones. The isoflavones are also known as phytoestrogens, or plant estrogens. They have estrogenic activity, but they are very weak estrogens, they have only about 1/1000 to 1/100,000 the potency of the natural female sex hormone, estrogen. However, soybeans contain very high concentrations of isoflavones and in people consuming soy, blood levels of isoflavones are many times higher than estrogen.
Conversely, the isoflavones do cause reproductive problems in some animals and in certain animal experiments have been shown to cause adverse effects on sexual development. However, I don't think you can extrapolate from these studies to humans. Soy infant formulas, which contain isoflavones, have been used for decades and there are no reports of adverse effects. Because estrogenic effects are likely to be very obvious in infants, you would think if there were adverse effects associated with consuming soy infant formula they would have been noticed over the years.
Although with respect to toxicity, the emphasis has been on infants, some concern has also been expressed with respect to children and pregnant women. One might think it foolish to worry about these groups considering that Asian countries have been consuming soyfoods for hundreds of years without apparent adverse effects. It has been argued however, that 1) Asian populations may have become insensitive to such effects over the generations and 2) without specifically looking for adverse effects, such effects may be overlooked.
So, where does this leave the consumer? First, bear in mind that to my knowledge, there has not been one human study demonstrating adverse effects of soy consumption (with the exception of allergenicity) and there have literally been hundreds of studies demonstrating positive effects. Second, as indicated above, no toxic effects have been observed in soyfood consuming countries. Of course, when it comes to infants, breast is best, but it does seem that soy formula is a reasonable substitute for those who can't breast feed. And certainly, I recommend that children and adults view soy as one other healthy food to add to the diet. I don't think there's anything to worry about."
Trevor Johnston, founder of Bean Supreme Ltd in New Zealand says "When I founded Bean Supreme in 1984 based on my enthusiasm for the future of soy products I never imagined that 10 years later in 1995 I would be spending 100s of hours and 1000s of dollars trying to prevent an irrational media juggernaut from destroying my livelihood and the credibility of soyfoods.
Some of you may have seen the headlines appearing in many of our daily newspapers: "Poisoned Protein", "Soy Under Suspecion", "Scientists call for soymilk ban", "Growth disorders reopen soy debate", etc. etc.
During that time I have received abusive letters from anti soy activists telling me that my company's products contain contraceptive pills and inferring that world renown researchers were being paid off by the soy industry, I have had journalists sneeringly ask me if my nephew fed on soy milk had "that transparent look" and implying that Japanese men were stunted and effeminate because of their consumption of soy products. Supposedly credible journalists have tried to associate soy food with rat poison and abortion remedies and have hissed at the soy industry's efforts to balance this tide of hysteria as a big business cover up and, yes, as we speak some legal vultures apparently have litigation dollars in their sights from understandably frightened people who have been encouraged to link unexplained health problems to soy consumed long ago in infancy.
If you think this is frightening you are right. Any remaining illusions I had about the media being custodians of truth and sources of reasoned argument based on impartial research has been completely shattered by this experience.
A few facts for the record: Not one of the so called experts trumpeting in the media about possible dangers in soy have conducted any clinical or laboratory research on soy nor are they nutritionists - obviously they don't consume soy themselves.
Major institutions charged with promoting and protecting public health in New Zealand such as the Ministry of Health, the Nutrition Foundation, and the Plunket society have all continued to endorse the safety of soy products including where medically required, or ethically preferred the feeding of soy formulas to infants. These three institutions especially the Ministry of Health has had access to a vast amount of data including that put forward by the anti soy lobby. The Ministry has also consulted with overseas regulatory authorities including the US FDA and the WHO.
There is a lot of information on the effects of soy consumption based on both animal and human research. Nowhere are there any human studies indicating any likely effects arising from the long term consumption of soy. Infact, on the contrary, studies indicate that soy is a high quality protein which supports normal growth and beyond this may have a significant role to play in reducing the risk of chronic diseases such as heart disease cancer and osteoporosis. Research is currently underway to see if it can assist women in minimising aggravating effects from menopause.
Moreover, both Asian populations which have a high intake of soy products, and vegetarians, have a statistically much lower incidence of many chronic diseases. Nowhere is there any evidence of the growth disorder scenario portended by the alarmists. Nor have our own customers ever alerted us to any health problems they might have had. On the contrary, we have had innumerable letters over the years expressing gratitude and satisfaction at the availability of our soy foods. I recently calculated that I have been happily consuming up to 40 grams of soy protein a day for ten years.
How did all this start you might ask? A Whangarei parrot breeder has been aggressively trying to link the death of his parrots to the presence in soybeans of minuscule quantities of compounds which could theoretically be toxic in isolation. He and a very small group of academics have extrapolated this into arguments about human health and have been thrusting themselves before the media at every opportunity since.
An irony in all this is that my own company has been supplying tofu as a significant ingredient in a mixed diet for Kiwis (birds) to several captive Kiwi houses for many years.
Dr John Birkbeck, the Medical and Scientific Director of the Nutrition Foundation, has told me that in his many years of exposure to public issues concerning nutrition and health has never seen anything quite as unbalanced or extreme as this.
In order to alleviate public fears aroused by this extremism I am pleased that the Plunket Society in association with the Ministry of Health and companies in the soy industry will shortly conduct a retrospective survey on the health of individuals who consume soy in infancy.
(1) James RF, James VA, Woodhams, DJ & Fitzpatrick MC, The Toxicity of Soybeans & Related Products, Auckland, New Zealand, 1994.
Irvine C, Fitzpatrick M, Robertson I, Woodham D, The potential adverse effects of soybean phytoestrogens in infant feeding, New Zealand Medical Journal, Vol 108, p183-4, 24 May 1995.
(2) Dwyer, JT. et al 1994. Tofu and soya drinks contain phytoestrogens. Jnl of the American Dietetic Association v.94 p.739-743.
(3) Estrogenic Soybean isoflavones and Chronic Disease, Risks and Benefits, Clarkson T, Anthony M & Hughes C, Trends Endocrinol Metab 1995;6:11-16.
(4) Sheeham SM, The case for expanded phytoestrogen research, Proc Soc Exp Biol Med 1995: 2082-6.
(5) Weaning and the Weaning Diet, Department of Health Committee on Medical Aspects of Food Policy report 45, HMSO, 1994.
Swimming in a Sea of Oestrogens by Sue Dibb (Co-Director of The Food Commission, London, UK). The Ecologist, Vol 25, no 1, January/February 1995.
Living Earth & Food Magazine. The Food Commission. January/March 1995 and April/June 1995.
Berrydale News 1.6.95.
The Vegetarian Society's Research Bulletin. December 1994.
Living Food Revolution by Kate Neil. Optimum Nutrition. Autumn 1995