soy bean is the darling of the health food industry these
days, and soy products are most highly and fraudulently touted
of all health food products. Reading all the popular press
on soy products, one would naturally believe that soy is a
panacea and ideal substitute for animal protein in human diets.
It is claimed that soy protein is of the same quality as animal
protein, yet lower in fat and devoid of cholesterol. Soy promoters
make many unsubstantiated claims, especially regarding soy
isoflavones, estrogen-like molecules (called xenoestrogens)
found the bean. It is claimed that these isoflavones from
soy products will prevent breast cancer and osteoporosis and
serve as estrogen replacements for post-menopausal women.
In fact, according to some prominent soy researchers, the
evidence for these claims is very weak (see below).
Promoters of soy commonly point to the low rates of heart
disease, breast and prostate cancer, osteoporosis, and symptoms
of menopause in Asia and claim that this is due to the "soy-based"
Asian diet. But it is a stretch of imagination to call the
Asian diet "soy-based". According to the non-profit
Soy On Line Service (www.soyonlineservice.co.nz), the typical
Japanese diet contains only 0.08 to 0.13 mg isoflavones per
kg of body weight per day. That means only 5.6 to 9.1 mg of
isoflavones per day for a 70 kg/154 lb. person. This amount
is found in about 8 grams-less than one third of an ounce-of
whole soybeans! Compare this to the average 3 to 4 pounds
of food eaten daily by the typical individual. One-third of
an ounce represents only 0.5 percent of the Japanese diet;
one ounce is 1.5 percent of the diet.
This pattern of soy consumption is found throughout Asia,
where soy is consumed primarily as a part of very salty fermented
seasonings, in the form of shoyu (wheat and soy sauce), tamari
(wheat-free soy sauce), or miso paste. Asians are not snacking
on soy "nuts", drinking soy milk, using isolated
soy protein, and eating tofu burgers or soy hot dogs three
times per day. Thus, Asians do not eat a soy-based diet! It
includes some soy but it is not a major article of diet as
implied by the word "based."
This casts doubt on the claim that soy is the secret to Asian
health. Consuming only as little as 9 grams of soy and 9 mg
of isoflavones per day, Asians purportedly have much lower
rates of heart disease, breast and prostate cancer, osteoporosis,
and menopause compared to Americans. Nevertheless, promoters
of soy are suggesting that protection from heart disease,
etc. requires consumption of 25 grams of soy protein per day,
which can provide up to 5 times as much isoflavones as found
in the typical Asian diet.
In addition, traditional fermented soy foods are quite different
from the processed soy foods promoted in "health food"
markets. Soy beans contain various harmful anti-nutrients,
including trypsin inhibitors that block protein digestion
and phytates that block mineral absorption. Traditional long
term fermenting (3 to 48 months) of soy beans to produce soy
sauces and miso pastes destroys significant amounts of these
anti-nutrients, whereas modern factory processing to produce
soy sauces, soy milk, tofu, and mock meats does not remove
those harmful elements.
Recently, in response to a petition submitted to the FDA by
Protein Technologies International (PTI), a division of DuPont
corporation that manufactures Supro® brand soy protein, the
FDA has allowed the following health claim to be attached
to soy products containing soy protein: "Diets low in
saturated fat and cholesterol that include 25 grams of soy
protein a day may reduce the risk of heart disease."
This claim was allowed supposedly based on some clinical trials
which show adding soy protein to a diet low in fat and cholesterol
will result in decreases in cholesterol beyond what occurs
as a result of a low-fat, low cholesterol diet alone. However,
other studies have not shown such a benefit. Therefore, the
allowed claim conveys uncertainty, by the phrase "may
reduce the risk..." Also note that the possible benefit
of soy consumption is promised only in conjunction with a
diet low in fat and cholesterol, which itself "may"
reduce the risk of heart disease (another uncertainty)-so
if your risk goes down when consuming soy as part of a low-fat,
low-cholesterol diet, is this due to the soy, or the diet?
Similar uncertainty exists with regard to soy and other putative
health benefits. Some studies have suggested that consuming
soy reduces hot flashes and other menopausal symptoms and
increases bone density among post-menopausal women-while others
Clearly, this is an experiment untried on a large scale. Promoters
of soy suggest that it is safe to consume soy in almost any
quantity but this has not been proven true. In fact, there
is some rather strong evidence that ingesting soy on a daily
basis, even in rather modest quantities, and certainly in
large quantities, may have serious adverse effects on endocrine
functions, immune system functions, and brain cell repair.
Here are the details:
Soy salesmen claim that soy protein is equal to animal protein.
Their claims are aided by the FDA's endorsement of the Protein
Digestibility Corrected Amino Acid Score (PDCAAS), which uses
soy protein as the standard. However, the PDCAAS disregards
digestibility, rating proteins only by their amino acid score;
and further, the FDA simply defined soy protein as the standard,
even though animal proteins have superior digestibility and
amino acid profiles. Outside the FDA, nutritional biochemists
still rate proteins according to biological value, and the
standard for biological value is human milk protein (an animal
protein), which is given a score of 100. The biological value
of soy protein is only 73, and all animal proteins rate superior
to soy protein on the scale of biological value, with egg
and whey protein at the top of the heap, equal to human milk.
Soy isoflavones are estrogen-like molecules. Environmental
toxicologists refer to such things as xenoestrogens. Many
health care professionals are extremely concerned that human
health is adversely affected by increasing intake of xenoestrogens,
including soy isoflavones, because they stimulate various
undesirable growth processes in girls and women, and may interfere
with normal hormone dependent development of boys and functional
capacities of men.
In 1997, researchers reported that "The daily exposure
of infants to isoflavones in soy infant formulas is 6- to
11 fold higher on a body weight basis than the dose that has
hormonal effects in adults consuming soy foods. Circulating
concentrations of isoflavones in the seven infants fed soy-based
formula were 13000-22000 times higher than plasma oestradiol
concentrations in early life, and may be sufficient to exert
biological effects, whereas the contribution of isoflavones
from breast-milk and cow-milk is negligible." [Lancet
1997 Jul 5, 350: 9070, 23-7]
In 1998 researchers from New Zealand reported that the rate
of isoflavone intake in infants fed soy-based formulas, cereals,
dinners, and biscuits "is much greater than that shown
in adult humans to alter reproductive hormones." They
advised: "Since the available evidence suggests that
infants can digest and absorb dietary phytoestrogens in active
forms and since neonates are generally more susceptible than
adults to perturbations of the sex steroid milieu, we suggest
that it would be highly desirable to study the effects of
soy isoflavones on steroid-dependent developmental processes
in human babies. [Proc Soc Exp Biol Med 1998 Mar 217: 3, 247-53]
Previous to these recent studies, in 1982, pediatric endocrinologists
in Puerto Rico reported an increase in the incidence of premature
breast development in girls under eight years of age. Of 130
cases studied, 85 involved breast development in girls under
18 months of age. Of those 85 cases, 22 were found associated
with use of soy formula, rich in isoflavones. [Am J Dis Child
1986 Dec 140: 12 1263-7]
The evidence for cancer preventive properties of soy foods
and isoflavones is rather weak.1 Some epidemiological studies
have shown a relation between soy consumption and protection
from breast and endometrial cancer, but they have not been
able to separate the effect of soy from that of other significant
factors of Asian diets, such as low fat and high fiber, fish,
whole grain, vegetable, fruit and non-soy legume intake-especially
since soy is such a small part of Asian diets. Meanwhile,
some clinical evidence suggests that high doses of isolated
soy protein and isoflavones (not parts of traditional Asian
diets) actually may be cancer promoters.
In 1996, one group of researchers fed 38 grams of soy protein
isolate containing 38 mg of isoflavones to both pre- and post-
menopausal women for five months. It is of interest to note
that these researchers reported "No changes were found
in plasma prolactin, sex hormone binding globulin, cholesterol,
high density lipoprotein cholesterol and triglyceride concentrations."[emphasis
added] Perhaps the women weren't also on a low fat, low cholesterol
diet? Or maybe they were on such a diet and that doesn't reliably
reduce cholesterol or tryglycerides either?
They did find, however, that there was a greater production
of breast fluid in premenopausal women during the months of
soy consumption, and "plasma estradiol [estrogen] concentrations
were elevated erratically throughout a 'composite' menstrual
cycle during the months of soy consumption." Further,
they reported "Of potential concern was the cytological
detection of epithelial hyperplasia in 7 of 24 women (29.2%)
during the months they were consuming soy protein isolate"
and they concluded "this pilot study indicates that prolonged
consumption of soy protein isolate has a stimulatory effect
on the premenopausal female breast, characterized by increased
secretion of breast fluid, the appearance of hyperplastic
[abnormal] epithelial cells, and elevated levels of plasma
estradiol." [Cancer Epidemiol Biomarkers Prev 1996 Oct
5: 10, 785-94]
In 1997, another group of researchers studied the effect of
soy isoflavone genistein on breast cancer cells and reported
that "dietary estrogens at low concentrations do not
act as antiestrogens but act like DDT and estradiol to stimulate
human breast cancer cells to enter the cell cycle" [Environ
Health Perspect 1997 Apr 105 Suppl 3, 633-6].
In the September 1998 issue of Cancer Research, William G
Helferich, Ph.D., from the University of Illinois, reported
that human estrogen-dependent breast cancer cells injected
into mice multiplied if the mice were fed genistein. Helferich
says "We've seen a lot of good research that genistein
is a cancer preventer, but it is dangerous to people who already
have cancer....Caution is warranted."2
An epidemiological study done in China found that high soy
intake did not provide protection from breast cancer ["Diet
and breast cancer in Shanghai and Yianjin, China," Br
J Cancer 1995 71: 1353-8]. At a recent conference on soy foods
and health, soy advocate and author of The Simple Soybean
and Your Health Mike Messina Ph.D. stated, "It's simply
not possible as yet to draw any conclusions about soy consumption
and cancer prevention, but further research is certainly warranted"
[Honolulu Star Bulletin 11/19/99, http://starbulletin.com/1999/11/19/news/story4.html].
This is completely contrary, of course, to the image of soy
presented by advertisers who would like women to believe that
ingesting soy will prevent breast cancer.
Other research has shown that some premenopausal women ingesting
60 grams of soy protein daily (45 mg isoflavones) have leutenizing
hormone levels 33% of normal and follicle stimulating hormone
levels only 53% of normal levels [Am J Clin Nutr 1994 Sep
60:3, 333-40]. These levels are low enough to inhibit ovulation
in some individuals. In 1994 a team of researchers reported
that in vitro "Genistein, and inhibitor of tyrosine kinases,
including c-kit, blocked oocyte growth and disrupted follicle
morphology." In translation, genistein blocked egg growth
and caused abnormal changes in the shape of the follicle [Dev
Biol 1994 Jan 161:1, 194-205].
There is good reason to suspect soy estrogens as a cause for
male infertility. Over the past 30 to 50 years, as human exposure
to xenoestrogens (including soy isoflavones, in so many processed
foods containing soy protein) has increased, there has also
been an increase in incidence of developmental disorders of
male reproductive organs and a decrease in sperm counts. Researchers
have found that soy isoflavones genistein and daidzein inhibit
the activity of an enzyme required for proper metabolism of
steroids critical to hormonal functions-in particular, this
enzyme is required for the production of testosterone. [Biochem
Biophys Res Commun 1995 Oct 24 215:3, 1137-44.]
Soy isoflavones have been shown to interfere with normal reproductive
functions on the cellular level. In 1996, researchers showed
that genistein is a strong inducer of DNA strand breaks, thus
clastogenic and mutagenic. [Food Chem Toxicol 1996, 35: 605-13]
In 1998, researchers reported that "coumestrol and genistein
are clastogenic in cultured mammalian cells and lead to gene
mutations."[Z Lebensm Unters Forsch A 1998, 206: 367-73]
Below we will report how this may affect the immune and nervous
Soy and Thyroid Function
A significant body of research has suggested that the estrogen-like
soy isoflavones in 25 grams of soy protein can seriously disrupt
other endocrine functions. In the late 1950s and early 1960s
there were reports that infants fed soy formula developed
goiter (enlarged thyroid). A study done in Japan in 1991 found
that diffuse goiter and hypothyroidism appeared in half of
the subjects after consuming 30 gm per day of pickled roasted
soybeans for three months [Ishisuki Y et Al., "The effects
on the thyroid gland of soybeans administered experimentally
in healthy subjects," Nippon Nibunpi Gawk Zasshi (1991)
In 1997 it was shown that the supposedly healthful soy estrogens/isoflavones
suppress thyroid activity.3 As thyroid inhibitors, soy isoflavones
are considered to be somewhat more potent than common anti-thyroid
drugs, working to inhibit action of an enzyme that converts
the amino acid tyrosine to thyroid hormone. Daniel R. Doerge,
Ph.D., one of the researchers from the FDA National Center
for Toxicological Research involved in the study that isolated
and studied the anti-thyroid mechanism of the soy isoflavones,
says: "I don't think you can get into trouble if you
eat a few soyfoods within the bounds of a balanced diet...But
I see substantial risks from taking soy supplements or eating
huge amounts of soy foods for their putative disease-preventive
value. There is definitely potential for interaction with
Soy and Immune Function
Several studies have shown that soy isoflavones suppress the
immune system. In fact, genistein has been studied as a potential
drug to give to transplant recipients, who are always given
immune suppressant drugs to prevent their bodies from rejecting
the foreign transplant tissues. One team of researchers studied
the immunosuppressive potential of genistein and reported,
"Our data suggest that genistein is a powerful immunosuppressive
agent, with no toxic effects on T cells, and has the potential
for use in the prophylaxis and treatment of allograft rejection"
[Transplantation 1991 Feb 51:2, 448-50]. In other words, genistein
has a immune suppressant effect comparable to that of immune
suppressant drugs given to transplant patients.
Other researchers have found that genistein works as an immune
suppressant by causing chromatin fragmentation [Biochem Biophys
Res Commun 1993 Jul 30 194:2, 944-50]. In 1998 researchers
reported that "Exposure of mammalian cells to genistein
results in DNA damage that is similar to that induced by the
topo-II inhibitor and chromosomal mutagen, m-amsa." These
researchers found that "genistein is a chromosomal mutagen"
that causes mutations and cell death of human lymph cells
[Mutat Res 1998 Aug 31 405:1, 41-56].
Soy and Brain Function
According to the Honolulu Star-Bulletin (11/9/99) newspaper,
ingestion of soy products has recently been strongly linked
to development of dementia. The National Institute of Aging
sponsored a study of 3, 634 Japanese-American men in Hawaii,
which found that those who ate the most tofu had the most
advanced dementia and on autopsy the brains of men who ate
more than two servings per week of tofu weighed less than
the brains of men who consumed fewer than two servings of
tofu per week. The rate of impairment was also found correlated
with soy intake. Those who ate no tofu showed mental abilities
of men five years younger, while those who ate the most tofu
tested as if they were five years older. Of 27 dietary items
checked, including meat, only soy was found consistently correlated
with increased incidence and severity of dementia [http://starbulletin.com/1999/11/19/news/story4.html].
This finding is supported by experimental evidence which has
shown that soy isoflavones decrease DNA repair and synthesis
in the brains of rats and mice [Yakisich JS, et Al, "Early
effects of protein kinase modulator on DNA synthesis in rat
cerebral cortex," Exp Neurol 1999 Sep; 159 (1): 164-76;
Schmitz C, Axmacher B, Sunker U, Korr H, "Age-related
changes of DNA repair and mitochondrial DNA synthesis in the
mouse brain," Acta Neuropathol (Berl) 1999; 97(1): 71-81]
According to the Star-Bulletin, this study linking tofu to
dementia was presented at a conference on soy and health sponsored
by soy foods producers such as DuPont and Archer Daniel Midlands.
Commenting on the conference, the lead investigator in the
Hawaii study, Dr. Lon White, stated "The majority of
scientists said the data they were talking about for beneficial
effects [of soy foods] on health is very weak" and doesn't
really support health claims for soy foods.
The Money Game
Thus, right now it appears that there is sufficient contradictory
evidence to conclude that we don't really know yet whether
ingesting soy in large amounts as food or as isoflavone supplements
will be beneficial or harmful. Obviously it is best not to
consume soy or its isoflavones in the large amounts recommended
by soy product manufacturers and "approved" by the
FDA. Until more is known, it would be best not to exceed the
levels of soy food consumption found in the typical Asian
diet, about 8 to 10 grams (one-third ounce) daily-and certainly
one should avoid using isolated soy protein or high dose soy
So why are soybeans so highly touted in the popular media?
Here is my hypothesis: Up until about 10 years ago, most of
the soy grown in the U.S. was fed to cattle or used for industrial
purposes, such as making margarine, paints, plastics, drugs,
cleaners, emulsifiers, and so on. However, there is a limit
to the profit to be made in this use of soy. You can make
much more money if you can get people to eat the soy-and especially
if you can get people to believe that it is the panacea for
many ills, since people willingly pay dearly for panaceas.
The soy pushers are some of the largest, wealthiest corporations
in the U.S. For example, Monsanto (the same corporation behind
rBGH mentioned above) markets its "Round Up Ready"
genetically engineered soybean along with its Round Up pesticide-the
soybean is engineered, not to be more nutritious or delicious,
but to be capable of withstanding larger doses of Round Up!
Another example is Archer Daniels Midland (a.k.a. ADM), which
advertises itself as "supermarket for the world,"
and is heavily invested in producing soy products. DuPont
Chemical is also involved in the soy market, through its subsidiary
Protein Technologies International, a soy protein powder maker.
Green Giant is selling soybean mock meats.
All of these big boys are interested in getting you to eat
soy, drink soy, and take soy pills. They don't really care
about your health, only about their profits. So you should
take all soy advertisements and popular articles and books
with a big grain of salt.
Don Matesz, M.A., C.N., C.R.T. is an associate member of the
International Association of Resistance Trainers and graduate
of the American Academy of Nutrition. Don resides in Toledo,
Ohio, and is available for fitness consultation by phone and
e-mail, and personal training in Toledo. Call (419) 476-2967
for rates and details. You can also reach Don by E-mailing:
Fitzpatrick M, "Soy Isoflavones: Panacea or Poison?",
submitted to the FDA in an effort to block GRAS status for
soy isoflavones, published in Health and Healing Wisdom, Volume
22, No 3, p. 3. Also available at www.soyonline.com.
2 Osborne SE, "Does Soy Have a Dark Side?", Natural
Health, March 1999, p. 158.
3 Divi RL et al., "Anti-thyroid isoflavones from the
soybean," Biochem Pharmacol (1997)54:1087-1096.
4 Osborne SE, op cit, p. 113.
This article edited
and reprinted by permission of