It True What They Say About Soy?
and their products, such as tofu (soybean curd) and soy milk,
enjoy a reputation as very healthy foods, and they have risen
in popularity. Certain soy foods have earned the right to be
labeled "heart-healthy." Yet not everybody is on board,
judging by a recent spate of queries from our readers. "I
won't allow soy in the house," one writes. Others ask if
soy can fuel breast cancer, cause thyroid disease, or promote
Alzheimer's. One unnerving report suggested that soy milk damages
infant immune systems. A lot of people these days are afraid
contain a complex mix of phytochemicals, including isoflavones.
Some of these may act as estrogens or as anti-estrogens (the
latter may block the effects of estrogens in the human body).
Soy isoflavones may also act as antioxidants and have other
beneficial effects on blood vessels and the heart. There's still
a lot to learn about soy.
and isoflavone supplements are in another category entirely.
Since they concentrate the hormone-like substances in soy, they
may well have a downside. Moreover, you have no guarantee as
to what's in the supplements, and too little is known about
them. We hope you will cross them off your list.
what about soy foods? First, here are the potential problems
and the conclusions so far:
cancer: The high intake of soy foods in Asian countries
has long been credited, at least by some researchers, for the
lower rate of breast cancer among Asian women, compared with
women in countries where little soy is consumed. But some confusion
arises when you look at genistein, the main soy isoflavone and
a plant estrogen. Does it protect against breast cancer or,
on the other hand, promote the growth of existing cancer cells?
Some studies have suggested the latter. Researchers at the Mayo
Clinic recently reviewed all the evidence and concluded that
soy has not been shown to fuel breast cancer cells. "If
breast cancer patients enjoy soy products," they concluded,
"it seems reason-able for them to continue to use them."
Whether soy actually protects against breast cancer is still
milk and infants: A study published last year in
the Proceedings of the National Academy of Sciences found that
the highly concentrated phytoestrogens in soy formula might
weaken the immune systems of babies. The formulas have more
of these compounds than soy foods do. But researchers emphasized
that this risk is largely theoretical. There's no evidence that
soy formula is unsafe, or that infants drinking it have been
harmed. Breast milk is still the first choice, however, followed
by milk-based formulas. Only infants allergic to milk should
drink soy formula.
disease: One study suggested that soy protein supplements
can interfere with the absorption of thyroid medications. Other
research tentatively showed that soy foods may actually interfere
with normal thyroid function, perhaps leading to goiter (swelling
of the thyroid gland, located in the neck). But there's no risk
of goiter in healthy people consuming soy who are not deficient
in iodine. Strict vegetarians, who eat no iodine-rich fish or
dairy products, might be at riskand eating lots of soy
might boost the risk. The answer is not to give up soy, but
to increase iodine intake. One way is to use a small amount
of iodized salt. And vary your diet as much as possible.
disease: As we reported two years ago, a study of
middle-aged Japanese-American men showed that those who ate
at least two servings of tofu a week had a faster decline in
mental ability as they aged and were more prone to Alzheimer's
than men who ate no tofu. But this study raised more questions
than it answered. No such effects have been seen in Japan, where
life expectancy is high and tofu is a staple of the diet. Indeed,
soy foods may actually protect the brain. The findings of this
study are questionable and should not lead you to avoid tofu
or other soy foods.
stones: If you've ever had calcium-oxalate kidney
stones, the most common type, you should limit your intake of
soy. Many soy foods are rich in oxalates and thus may promote
the formation of such stones in those at risk, according to
a study last year.
a look at the positive side of soy foods. Not much is certain,
but the outlook is promising:
disease: Many researchers believe that the high intake
of soy in Asian countries helps explain the lower incidence
of heart disease there, and the FDA has okayed a "heart-healthy"
claim for soy foods. Those that contain at least 6.25 grams
(about one-quarter of an ounce) of soy protein per serving can
claim on the label to reduce the risk of heart disease, when
consumed as part of a healthy diet. Soy helps lower high blood
cholesterol and may work in other ways to benefit blood vessels
and the heart. So far, of all the potential health benefits
of soy, this one has the most solid evidence.
cancer: In countries where soy is a dietary staple,
men are less likely to develop prostate cancer. In animal studies,
soy has slowed the growth of this cancer. This anti-cancer effect
is still only hypothetical; more research is needed.
symptoms: Soy supplements (capsules or pills) containing
high levels of isoflavones, as well as soy foods with lower
levels, have been promoted as effective remedies for menopausal
symptoms such as hot flashes, irregular sleep patterns, and
vaginal dryness. But no one knows how effective these plant
hormones arethe evidence is contradictoryor whether
they are safe. If isoflavone supplements act like hormones,
they could pose some of the same dangers. Soy foods, on the
other hand, may not have enough plant hormones to combat menopausal
symptoms, but at least they aren't harmful. It can't hurt to
try them, as part of a healthy diet.
According to research in Japan, women who consume a lot
of soy tend to have greater bone mass. Japanese women also have
a lower rate of hip fractures than American women, but that
might be because of genetics or other factors. So far, there's
reason to think that consuming soy is beneficial to bones, but
long-term studies are still needed.
in mind: Soy foods are well worth adding to your
diet, since they may reduce the risk of heart disease. Other
possible health benefitsnot so well establishedinclude
protection against breast and prostate cancer and osteoporosis.
Soy is not magical; it cannot fix up a poor diet. On the other
hand, there is no convincing evidence that soy foods are harmful.
People have been eating them for millennia, particularly in
Asia. Remember that not all soy products are created equalsoy
sauce, for instance, contains no soy protein. Even soy foods
with a heart-healthy label may be high in salt, sugar, and calories.
Be sure to read the labels.
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