Soy
Foods and Cancer
A
1990 National Cancer Institute workshop identified 5 different classes
of anticarcinogens in soybeans. These are phytoestroles, phytates,
saponines, protease inhibitors and isoflavones. Soy is also rich
in phenolic acids, many in which contains anticarcinogens, and the
two isoflavones: genistein and daidzein. Isoflavones are weak estrogens
that help protect against breast, ovarian and prostate cancer by
inhibiting the growth of hormone-dependent tumors. Since high blood
levels of estrogen are an established risk factor for breast cancer,
weak estrogen have been postulated as being protective against this
form of cancer. Observation of populations that consumed a high
quality of soy product supports this hypothesis. The Japanese breast
cancer mortality rate, for example, is only one-fourth than that
of the United States. Isoflavone genistein inhibits the growth of
both estrogen-dependent and estrogen-independent breast cells. In
1987, Japanese researchers showed that genistein inhibits the activity
of the enzyme tyrosine protein kinase (TPK), the enzyme that is
involved in controlling cell growth and regulation. In more than
20 studies, several researchers have found that the consumption
of just 1 serving of soy per day is associated with a reduced risk
of several types of cancers especially breast, prostate, lung, rectal,
colon, and stomach cancers.
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Soy
foods and Heart Disease
More
than 40 studies conducted over the past 25 years have shown that
adding as little as one serving of soy to our diet helps protect
against cardiovascular diseases such as heart disease and stroke.
One serving of soy is equivalent to 25 grams of soy protein or about
1 cup of cooked soy beans. Several theories on the effect of soy
on blood cholesterol profiles have been proposed; these are increased
thyroxin levels, decreased insulin: glucagon ratio and increased
hepatic LDL-receptor activity in response to soy protein ingestion.
Isoflavone globulin helps in cholesterol clearance by the liver;
and isoflavone saponine helps in cholesterol excretion from the
body. Studies have also shown that phytoestrogen helps increase
HDL "good" cholesterol level and genistein acts as a tyrosine
kinase inhibitor that decreases thrombosis (blood clotting) protecting
against cardiovascular diseases such as heart disease and stroke.
Isoflavones in soy also act as an antioxidants that help in preventing
LDL "bad" cholesterol oxidation protecting against atherosclerosis
(plaques build up in the arteries). Atherosclerotic plaque are considered
to be the primary cause of cardiovascular diseases such as heart
disease and stroke. In one study, when subjects consumed soy daily
for 6 months, cholesterol oxidation was about 50 percent lower in
comparison to the control group.
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Soy
foods and Women's Health
Bone
Health: Osteoporosis
is a worldwide health problem especially among post menopausal women.
After menopause, women usually experience dramatic increase in bone
loss and it is estimated that they might lose as much as 15 to 50%
of their bone mass in the first 10 years following menopause. There
are many factors that affect bone health, these factors are genetics,
exercise, and diet. Many studies have shown that soy exhibits a
positive effect in the bones. Soy provides an important source of
calcium, and it have been shown that calcium absorption from soy
is equivalent to that of other kinds of milk. Approximately 30 to
40% of the calcium from various soy products such as soy milk, tofu
and soybeans is absorbed. Soy also contains isoflavones (daidzein
and genistein), compounds that may directly inhibit bone resorption
(loss of calcium from the bone). It has been shown that isoflavones
are nearly identical in chemical structure to estrogen, and that
they exhibit the same effect the potent anti estrogen tamoxifen
has in our bones protecting against osteoporosis. Isoflavones are
also nearly identical in structure to the drug ipriflavones, which
has been used successfully in both Asia and Europe to treat osteoporosis.
Soy is also known to be a high quality protein that favorably affects
calcium metabolism as compared to other high quality proteins. This
has been proven by a study done on human subjects fed diets that
differ only in the type of protein consumed. The control group that
consumed only animal-based protein excreted 150 mg of calcium per
day compared to only 103 mg of calcium per day by the other group
that consumed soy-based protein.
Also,
a recent study by the Division of Nutritional Science, University
of Illinois at Champaign-Urbana, entitled "Short-Term Effects
of Soybean Isoflavones on Bones in Post-Menopausal Women,"
found that post-menopausal women with high concentrations of soy
in their diet had stronger bone health. Read about this study and
more findings about the benefits of soy for bone health at www.OBGYN.net:
Soy
And Osteoporosis: Studies Show Soy Protein May Help in Prevention
and Treatment of Bone Loss.
Breast
Cancer is
the second most common cause of death in American women and is the
first cause of death in those between the age of 35 and 44.
American women are four times more likely to die from breast cancer
as compared to the Japanese women. This is most likely, as most
of the studies have shown over the past 25 years, to be due to the
large consumption of soy products among the Japanese. Soy foods
are rich in isoflavone genistein, containing as much as 1 mg per
gram of soy food (dry weight). Genistein has been shown to inhibit
estrogen-dependent breast cancer and to exhibit very weak estrogen
activity. This weak estrogen activity is shown to act as antiestrogens
and interferes with the growth of estrogen-dependent tumors. Isoflavone
genistein is also shown to inhibit breast cancer cells that are
estrogen-independent. (see bone health above). One serving of soy
food per day is shown to be associated with reduced cancer risk.
Menopause:
The
decrease of estrogen during menopause produces a variety of symptoms
such as night sweat and hot flashes. The estrogenic activity of
soybean isoflavone genistein has shown in many studies to offset
the effects of reduced estrogen production by the ovaries. Studies
have shown that in women consuming soy foods, blood levels of isoflavones
can be 1,000 times higher than endogenously produced estrogen levels.
And in recent Australian study, researchers found that women who
consumed 45 grams of soy flour per day experienced a 40 percent
decrease in menopausal symptoms.
Fertility:
A
recent study found that soy consumption increased the length of
menstrual cycle by an average of 2.5 days. Soy consumption was also
associated with a marked decrease in both follicle-stimulating hormone
(FSH) and luteinizing hormone (LH) levels. The decrease in LH levels
has lead to speculation that soy might interfere with ovulation.
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