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- Soy has been hailed as a wonder food for several conditions,
including heart disease, breast cancer, prostate cancer, menopausal symptoms
and bone health.
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- Yet recent media reports suggest that it may be harmful,
a view spearheaded by an article in Nexus magazine. The piece was critical
of soy products, though the data on which it was based referred mainly
to whole soy beans rather than soy products such as tofu and soy milk.
Most soy-based products are processed, which destroys or minimises the
"anti-nutrients discussed in the article.
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- The report denounced soy protein isolates (SPIs), which
are processed differently from tofu and are used by the food industry as
"hidden bulking agents for many foods, including baby formulas. SPIs
have been criticised for high aluminium levels because of the way that
they are processed. Good-quality brands of soy products such as milks,
desserts and yoghurt have low levels of aluminium; in soy milk it is less
than that found in water and in cow,s milk.
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- It is worth understanding why soy is supposed to be so
beneficial. The British Nutrition Foundation (BNF) says that compounds
in soy, isoflavones, have been shown to have oestrogenic and anti-oestrogenic
effects. They vie with a human oestrogen, oestradiol, to bind with the
oestrogen receptors in cells, but on binding they fail to stimulate a full
oestrogenic response, and evidence is building that this may offer protection
against a range of hormone-related conditions, including breast, bowel,
prostate and other cancers and, possibly, menopausal symptoms.
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- Isoflavones also have strong antioxidant properties,
and soy is a source of soluble fibre that can lower cholesterol levels.
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- Some experts believe that "foreign oestrogens to
which we are exposed in our environment " the xenoestrogens that come
from plastics, pesticides and dioxins " can be crowded out by soy
isoflavones, rendering them less capable of creating the hormone havoc
of which they are suspected.
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- In her book Our Stolen Future, Theo Colborn accuses these
environmental oestrogens of being involved in breast and other cancers,
as well as lowered sperm counts in men and malformed genitals in baby boys.
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- After menopause, when fewer oestrogens are available
" increasing the risk of osteoporosis and heart disease " isoflavones
are thought to act as weak hormone replacement therapy because of their
mildly oestrogenic effect, which seems to improve the prognosis for these
conditions.
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- The US Food & Drug Administration has approved a
health claim on foods that contain 6.25g of soy protein per serving. US
manufacturers are allowed to state that eating 25g of soy protein a day,
as part of a diet low in fat and cholesterol, may reduce the risk of heart
disease.
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- The FDA declined to say that isoflavones were responsible
for aiding heart health, but instead agreed that the whole soy protein
conferred protection.
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- So what about the criticisms? While isoflavones have
excited the most research, it is probable that other compounds in the soy
bean are partially responsible for the overall effect.
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- Probably the main criticism is of claims by supplement
manufacturers extolling the virtues of isolated soy isoflavones for conditions
such as breast cancer, heart disease and menopausal symptoms. Shelves in
health-food shops are laden with such supplements.
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- In fact, there is concern that these supplements could
actually increase the risk of breast cancer if taken to excess, and some
supplement manufacturers have marketed high-dose isoflavone supplements
for breast enhancement, which is patently a bad idea. To be on the safe
side, and in the absence of solid research evidence, it is safest to advise
those with breast cancer not to take supplements that contain isolated
isoflavones.
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- Professor Keith Griffiths is researching the effects
of isoflavones on prostate cancer at the Tenovus Cancer Research Centre
at the University of Wales College of Medicine. "Isoflavones stand
out as compounds that stop prostate cancers developing into their aggressive
form, he says. "But we use complete soy protein in the research because,
while we believe isoflavones are the interesting compounds, we might be
missing something if we use them in isolation. Similar factors are involved
in breast and prostate cancer.
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- The point has been made that while Japanese and other
Eastern cultures enjoy substantially lower incidences of breast cancer,
their diet is so different from that in the West that many other factors
must be considered. In my book about diet and breast cancer, eating soy
is the fifth of 12 points covered. I recommend eating fruit and vegetables,
oily fish and pulses and changing the fats in the diet, and only then eating
around 100g (4oz) of tofu (or similar) five times a week (equivalent to
70g daily). A bit of what you fancy may do you good, a lot may do the opposite.
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- Stephen Terrass, the director of Solgar Vitamins and
a nutrition expert, says: "If future research were to corroborate
recent safety concerns, it would likely be relative to the quantity of
soy consumed rather than inherent problems with isoflavone-rich foods.
No food can be consumed in unlimited quantities.
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- There have also been suggestions that soy is linked to
suppressed thyroid function, increased risk of Alzheimer,s disease, mineral
deficiencies and possible effects on fetuses. Pointing out that much of
the research cited to support these claims has been based on work with
animals rather than human beings, the BNF regards them as "speculative
and unproven.
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- The authors of a paper on tofu consumption and brain
aging published in the Journal of the American College of Nutrition note
in their conclusions that the men who ate the most tofu were more likely
to have spent their childhood in Japan and in greater poverty, and that
a nutritionally deprived childhood was more likely to be responsible for
ageing of the brain than tofu intake.
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- Some people are sensitive, or allergic, to soy and there
is no rule that we must obtain isoflavones from just this source. Other
foods rich in these compounds include chickpeas, beans, pulses, grains,
nuts, vegetables and fruits, and isoflavone levels are also higher in the
Mediterranean diet, which features these foods.
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- But if soy agrees with you, eating a moderate amount
as part of a mixed diet is likely to do more good than harm. I had breast
cancer 12 years ago and still eat it.
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