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Soy has shown great promise in reducing the uncomfortable
hot flashes of menopause, and new research indicates that
it may also help protect against certain chronic diseases,
including osteoporosis, heart disease, and some cancers.
What Is It
Found in soybean products such as tofu and soy milk, and sold
in supplement form, isoflavones are powerful compounds known
as phytoestrogens. These plant-based substances are chemically
similar to the hormone estrogen, produced in the body, but
are much weaker. Phytoestrogens, however, can bind to estrogen
receptors in the cells and produce various important health
benefits. Most research on soy isoflavones has been done with
people who regularly ate soy products, so even though most
supplements contain the major isoflavones in soybeans, genistein
and daidzein, it’s not clear whether isoflavones are
the only beneficial compounds in soy.
What Does It Do
As phytoestrogens, soy isoflavones have two important effects.
First, when estrogen levels are high, phytoestrogens can block
the more potent forms of estrogen produced by the body and
may help prevent hormone-driven diseases, such as breast cancer.
Second, when estrogen levels are low, as they are after menopause,
phytoestrogens can substitute for the body’s own estrogen,
possibly reducing hot flashes and preserving bones. Soy isoflavones
may also have antioxidant and anticoagulant effects.
Common Uses
• Reduce the frequency and severity of hot flashes and
other menopausal symptoms.
• May protect against coronary heart disease.
• May forestall certain cancers.
• May help prevent osteoporosis.
Prevention
Research indicates that soybean products help protect against
heart disease by lowering LDL (‘bad”) cholesterol,
and significantly increasing HDL (‘good’) cholesterol.
Soy seems most effective in people with high cholesterol levels.
In those with near-normal cholesterol levels, its effects
are less powerful, and larger amounts are needed to produce
the same benefits. Soy products may also inhibit the oxidation
of LDL cholesterol, the first step in the accumulation of
artery-clogging plaque. In addition, laboratory studies show
the genistein in soy helps prevent blood clots from forming.
In Asian countries where soy is a dietary staple, rates of
certain cancers are much lower than they are in the United
States. Preliminary studies indicate that regular consumption
of soy foods or supplements may protect against cancers of
the breast, prostate, and endometrium. And in animal studies,
adding soy protein to the diet significantly reduces tumor
formation and the likelihood that cancer, once developed,
will spread. The phytoestrogens in the soy are most likely
responsible for this effect. Researchers speculate that the
isoflavone genistein may block a protein called tyrosine kinase,
which promotes the growth and proliferation of tumor cells.
This effect may be why soy is also associated with a lower
risk of prostate cancer. Genistein has potent antioxidant properties as well, and for these reasons, it may one day
prove useful against cancer, though more research is clearly
needed.
Additional Benefits
Studies show that hot flashes and other symptoms of menopause
are relatively rare in Asia, where women eat a lot of soy
products. In addition, in one Western study, women who added
45 grams of soy flour to their daily diet experienced a 40%
reduction in hot flashes.
Soy isoflavones may also help women maintain bone density.
One study of postmenopausal women found that consuming 40
grams of soy protein a day resulted in a significant increase
in bone mineral density in the spine, an area often weakened
by osteoporosis.
How To Take It
Dosage: Experts don’t know the amount of soy
isoflavones needed to produce a therapeutic effect. In Asian
countries, the isoflavone consumption ranges from 25 to 200
mg a day. Some researchers believe that an intake of 50 to
120 mg a day might be the minimum amount necessary. The supplements
on the market vary in the types of isoflavones they contain
and the total amount of isoflavones per pill. Choose a product
that supplies a mixture of isoflavones (it should include
both genistein and daidzein) and take enough pills to obtain
50 to 100 mg isoflavones a day.
Guidelines For Use: Most experts recommend
that you try to get your soy isoflavones from soy foods. In
addition to their isoflavone content, these foods are good
sources of protein, so they can replace red meat and other
foods high in saturated fat.
The amount of isoflavones in soybeans, and therefore any product
made from them varies. In general, eating one to two servings
of soy products a day is probably sufficient. (A serving equals:
3.5 ounces tofu or miso, 1 cup soy milk, or 1/2 cup soy flour,
cooked soybeans, or textured vegetable protein.) If eating
this much soy is not to your taste, you might want to get
your isoflavones from a combination of foods and supplements.
Another alternative is soy powder, which contains both soy
protein and isoflavones; mix it into juice, milk, or shakes.
Take soy supplements with a large glass of warm water right
before eating breakfast and dinner.
Possible Side Effects
Soy products, even in large quantities, are not known to produce
side effects. However, the small percentage of people who
are allergic to soybeans should avoid all soy supplements
and soy-based foods.
Facts and Tips
A diet high in fiber may interfere with the absorption of
isoflavones. If you eat a high-fiber diet, be sure to increase
your consumption of soy supplements or soy foods. Even though
they’re made from soybeans, soy sauce and soybean oil
contain no isoflavones.
Latest Findings
• In a recent study, people with moderately high cholesterol
levels drank a daily “milkshake” containing 25
grams of soy protein, either with or without isoflavones.
After nine weeks, those who consumed the isoflavone-rich shake
experienced, on average, a 5% reduction in LDL (“bad”)
cholesterol levels. People with the highest LDL levels had
an 11% drop. (For each 10% to 15% drop in LDL levels, the
risk of a heart attack decreases 20% to 25%.)
• Women who ate the most soy products and other foods
rich in phytoestrogens reduced their risk of endometrial cancer
by 54%, according to one study. Soy products may be especially
important for women who have never been pregnant. Among this
group, eating less than an average of 1/4 ounce of soy products
a day was associated with a fourfold increase in the risk
of endometrial cancer.
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