Phytoestrogens
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.
Drugs
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.
References
(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