Do
Soy Foods Negatively Affect Your Thyroid?
A Look at the Downsides of Soy
by Mary Shomon
It seems that there's isn't a newspaper, magazine or news
program that hasn't recently featured a story on the amazing
health benefits of soy food products and soy/isoflavone
supplements. Soy is promoted as a healthy alternative to
estrogen replacement for some women, as a possibly way to
reduce the risk of breast cancer, as a way to minimize menopause
symptoms, and as a healthier, low-fat protein alternative
for meats and poultry. But what all the positive stories
fail to mention is that there is a very real -- but very
overlooked -- downside to the heavy or long-term use of
soy products.
Soy products increase the risk of thyroid disease. And
this danger is particularly great for infants on soy formula.
This is not information that the powerful and profitable
U.S. soy industry wants you to know. The sale of soy products
is big business, and the increasing demand for soy protein
products, soy powders and soy isoflavone supplements is
making that an even more profitable business than ever before.
In researching my book, Living Well With Hypothyroidism,
which covers the issue of soy products and the thyroid in
great depth, I talked to Dr. Mike Fitzpatrick, an environmental
scientist and phytoestrogen researcher who has conducted
in-depth studies on soy, particularly the use of soy formulas.
Dr. Fitzpatrick makes it clear that soy products can have
a detrminental affect on both adults and infants. In particular,
he firmly believe that soy formula manufacturers should
remove the isoflavones -- that part of the soy products
that act as anti-thyroid agents -- from their products.
Researchers have identified that the isoflavones act as
potent anti-thyroid agents, and are capable of suppressing
thyroid function, and causing or worsening hypothyroidism.
Soy is a phytoestrogen, and therefore acts in the body much
like a hormone, so it's no surprise that it interacts with
the delicate balance of the thyroid's hormonal systems.
High consumption of soy products are also proven to cause
goiter, (Anti-thyroid isoflavones from soybean: isolation,
characterization, and mechanisms of action, Divi RL; Chang
HC; Doerge DR, National Center for Toxicological Research,
Jefferson, AR 72079, USA, Biochem Pharmacol, 1997 Nov, 54:10,
1087-96)
Note: The best source of information on soy and its negative
impact on health can be found at the Soy Online Service,
and in particular, its page on phytoestrogenic effects of
soy, and impact on the thyroid.
Isoflavones belong to the flavonoid or bioflavonoid family
of chemicals, and are considered endocrine disruptors --
plants or other products that act as hormones, disrupting
the endocrine system, and in some cases, this disruption
involves acting as an anti-thyroid agent. (The grain millet,
for example, contains high levels of flavonoids, and is
commonly known as problematic for thyroid function). Flavonoids
inhibit thyroid peroxidase (TPO), which disturbs proper
thyroid function.
The March 1999 issue of Natural Health magazine has a feature
on soy that quotes Daniel R. Doerge, Ph.D., a researcher
at the Food and Drug Aministration's National Center for
Toxicological Research. Dr. Doerge has researched soy's
anti-thyroid properties, and has said "...I see substantial
risks from taking soy supplements or eating huge amounts
of soyfoods for their putative disease preventive value.
There is definitely potential for interaction with the thyroid."
One UK study of premenopausal women gave 60 grams of soy
protein per day for one month. This was found to disrupt
the menstrual cycle, with the effects of the isoflavones
continuing for a full three months after stopping the soy
in the diet. Isoflavones are also known to modify fertility
and change sex hormone status. Isoflavones have been shown
to have serious health effects -- including infertility,
thyroid disease or liver disease -- on a number of mammals.
Dr. Fitzpatrick believes that people with hypothyroidism
should avoid soy products, because, "any inhibition
of TPO will clearly work against anyone trying to correct
an hypothyroid state." In addition, he believes that
the current promotion of soy as a health food will result
in an increase in thyroid disorders.
The Dangers of Soy Formulas
Since the late 1950's, it has been known that soy formulas
contain anti-thyroid agents. Infants on soy formula are
particularly vulnerable to developing autoimmune thyroid
disease when exposed to high exposure of isoflavones over
time. ( Breast and soy-formula feedings in early infancy
and the prevalence of autoimmune thyroid disease in children.
Fort P; Moses N; Fasano M; Goldberg T; Lifshitz F Department
of Pediatrics, North Shore University Hospital-Cornell University
Medical College, Manhasset, New York 11030. J Am Coll Nutr,
1990 Apr, 9:2, 164-7) This study found that the frequency
of feedings with soy-based milk formulas in early life was
noticeably higher in children with autoimmune thyroid disease,
and thyroid problems were almost triple in those soy formula-fed
children compared to their siblings and healthy unrelated
children. Dr. Fitzpatrick even believes that long-term feeding
with soy formulas inhibits TPO to such an extent that long-term
elevated TSH levels can also raise the risk of thyroid cancer.
Not much is being done in the U.S. to make parents aware
of the thyroid-related dangers of soy formulas, or to alert
the public that heavy soy consumption may be a danger to
thyroid function. Other countries, however, are far ahead
of the U.S. In July of 1996, the British Department of Health
issued a warning that the phytoestrogens found in soy-based
infant formulas could adversely affect infant health. The
warning was clear, indicating that soy formula should only
be given to babies on the advice of a health professional.
They advised that babies who cannot be breastfed or who
have allergies to other formulas be given alternatives to
soy-based formulas.
Why more information is not available about these concerns
is probably a function of the tremendous strength of the
large agricultural companies that dominate America's soy
market. One thing is clear, however. At the same time that
health experts, and nearly every radio and television health
program in the nation touts soy as the miracle health food
of the new millenium, the United States pediatric and medical
community needs to get more on top of this issue, and begin
to counsel their patients regarding the serious impact use
of soy products can have on thyroid function.
How Much Soy is Safe?
According to the Soy Online Service, for infants, any soy
is too much. For adults, just 30 mg of soy isoflavones per
day is the amount found to have a negative impact on thyroid
function. This amount of soy isoflavones is found in just
5-8 ounces of soy milk, or 1.5 ounces of miso. For more
information on how much soy is too much, see the Soy Online
Service guidance page.
The USDA has launched a website that is promoting the health
benefits of use of soy and soy foods. The USDA site lists
the isoflavone content of a total of 128 foods, including
foods such as vegetarian hot dogs soybeans, chickpeas and
tofu. This can help you in deciding how much soy to include
in your diet.
More information
For more information on soy products, see:
* Soy Online Service
* Concerns Regarding Soybeans, from the Rheumatic Diseases
website
* Are Soy Products Dangerous?, from the Gerson Healing Newsletter,
Vol. 11, No. 5, Sep./Oct. 1997
* Guide to Soy Isoflavones
* Soy to the World: A Guide to Incorporating Soy into Your
Diet
