One minute it's the answer to all our health problems, the next it’s a hidden
hazard. From tofu to edamame, soy has
become a staple in our diets, though most
of us are still buckling at the knees at the long
list of supposed side effects. With so many
studies on soy published each year, it’s easy
to misinterpret the scientific literature, say
the experts.
So is soy a champion superfood or should
you strike it from your grocery list? We
went to the experts and pored over the latest
research to clear up the controversy.
The claim: Soy causes cancer
What you heard: The plant estrogen in
soy is linked to breast and prostate cancer.
What we found: Soy contains antioxidants
called isoflavones, which are plant estrogens
thought to mimic the hormone in our
bodies. “Isoflavones are commonly equated
with human estrogen [which is linked to
some cancers], so there is concern that by
extension, soy foods could have the same
harmful effects,” says Mark Messina, an
associate professor at Loma Linda University
in southern California and the executive
director of the Soy Nutrition Institute.
But the research is mixed. While it’s true
that scientists have found that soy’s isoflavones
can speed up cancer-cell growth in test
tubes, the American Institute for Cancer
Research suggests those findings may be
skewed by the large amounts of isoflavones
used in the experiments—equivalent to five to 16 times the amount commonly consumed
in Asia, where cancer rates are lower than in
North America.
Most studies done with humans, on the
other hand, show no link between soy and
cancer, or they suggest soy eaters have lower
rates of cancer than non-soy eaters, says
Alison M. Duncan, associate professor of
human health and nutritional sciences at
the University of Guelph. And some suggest
eating soy foods, particularly during the
teen years, can help reduce the risk of breast
cancer later in life.
Even breast-cancer survivors seem to
fare better when they consume some soy.
A recent study published in the Journal of the
American Medical Association that looked at
women diagnosed with breast cancer found
those who consumed about nine g of soy protein
per day over the study’s four-year period
were 31 percent less likely to have their
breast cancer recur and 28 percent more
likely to survive than those who consumed
half that amount.
Things are looking up for the guys, too.
A recent literature review published in the
American Journal of Clinical Nutrition
analyzed 14 studies and reported that men
who consumed soy were 26 percent less
likely to develop prostate cancer.
The claim: Soy makes menopause worse
What you heard: Eating soy intensifies
menopause symptoms, such as bone depletion
and hot flashes.
What we found: A recent study that looked
at 180 post-menopausal women who weren’t
on hormone-replacement therapy suggests
soy may actually help reduce hot flashes.
Health Canada also allows manufacturers
to make claims on their labels that daily
soy-isoflavone supplements of 30 to 100 mg
alleviate menopause symptoms. But it
cautions some women, like those who have
had breast cancer or who are taking hormone-replacement
therapy, against exceeding 30 mg.
Other studies have found bone-mineral
density diminishes slightly in post-menopausal
women, regardless of soy consumption. “Soy
provides bio-available calcium and high-quality
protein, both of which are important in retaining
bone health,” says Messina.
The claim: Soy makes you fat
What you heard: Soy causes weight gain
and thyroid problems.
What we found: There’s no proven link
between weight gain and soy. In fact, some
studies in laboratory rats and incubated
human fat cells have shown that soybeans
might actually prevent fat accumulation,
but there isn’t enough evidence to confirm
the same results in humans. Furthermore,
because protein is more filling than fat or
carbs, soy (one of the few vegetable sources
that are complete proteins) is more likely to
help you trim down. As for the claims that
soy interferes with thyroid function,
recent studies have seen this happen only
in iodine-deficient people (rare in North
America) or those already suffering from
thyroid problems, such as hypothyroidism.
The claim: Soy makes your man infertile...and busty
What you heard: Soy lowers his sperm count
and gives him man boobs.
What we found: Several studies, including
one from the University of Guelph just last
year, report that eating soy has no effect
on sperm quality. As for your guy’s cup size
surpassing yours, don’t be too concerned.
The man who made headlines because he
developed breasts was drinking 12 cups of
soy milk a day, far beyond a healthy amount
by anyone’s standards. “A man can consume
up to six servings per day of soy, and it won’t affect his estrogen levels,” says Messina. The
key is moderation and common sense.
The claim: Fermented soy is best
What you heard: Fermented soy (tempeh or
miso) is healthier than non-fermented soy.
What we found: Some experts speculate that
the nutrients in fermented soy are easier to absorb, since they’re already partially broken
down, says registered dietitian Mary Bamford
in Toronto. But this has yet to be proven. The
soy foods to avoid, say the experts, are heavily
processed ones—like fake deli meats, chicken
nuggets and hot dogs—which are often loaded
with preservatives, chemicals and sodium.
The claim: Soy is not heart-healthy
What you heard: Soy doesn’t lower your risk
of cardiovascular disease.
What we found: Some studies have shown
soy lowers LDL, the so-called bad cholesterol,
but others haven’t found a relationship
between soy consumption and heart health.
As a result, the FDA stopped allowing food
manufacturers to label soy products as
“heart-healthy” in 2008. Health Canada
also doesn’t allow manufacturers to make
“heart-healthy” claims on food labels.
Despite this, soy has been shown to lower
blood pressure, says Messina. “And soy is
low in saturated fat and high in polyunsaturated
fat. It has omega-3 fatty acids and
modestly lowers blood-cholesterol levels, and
isoflavones improve arterial health.” In other
words, it’s not a bad idea to choose soy as a
protein substitute for red meat and dairy,
which are high in saturated fat and cholesterol.
The claim: All soy is GMO
What you heard: Soy tops the list of genetically
modified organisms.
What we found: It’s true that a large part of
the soy crop around the world is genetically
modified, but the tofu, edamame and soy milk
you see on grocery-store shelves in Canada
are unlikely to come from GMO soy. If you’re
concerned, there’s no way to determine by
the label, but if you call the companies and
ask, they’re required by law to tell you.
The bottom line: For now, the soybean packs
plenty of promise as a healthy
food choice with a bright future.
Look for organic, real-food
sources, such as edamame, tofu,
miso and tempeh, and include
them in your diet a few times a
week — not because more is
harmful, but because variety
and moderation are the cornerstones
of a healthy diet.