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Men Don’t
Need to Fear Soy Foods
It’s no wonder that men
who have read the recent stories circulating about soy are confused.
Some stories claim that soy foods, such as tofu and soy milk,
can lead to breast growth or reduce testosterone levels. Other
stories tout the benefits of soy, suggesting soy may help protect
against prostate cancer. Women have wondered for years whether
phytoestrogens affect their health, from menopausal hot flashes
to breast cancer. Now men are left to wonder about soy foods
possible unwanted effects.
Soy contains compounds called
isoflavones that are known as phytoestrogens, which are weak
plant versions of the hormone estrogen. Fears that the amount
of phytoestrogens in moderate amounts of soy foods could stimulate
men’s breast tissue or reduce their testosterone are not
based on sound research. A study of children fed soy protein
formula for more than six months showed no hormonal effects.
A study of men in their 50s and 60s found that the men who ate
soy foods twice a day for three months showed no change in testosterone
levels, but had a 14 percent drop in levels of PSA (an indicator
of prostate growth used in screening for prostate cancer). |
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Concerns about lowering sperm
count and affecting fertility also do not seem to hold up in
human studies of realistic dietary consumption.
Whether or not soy foods offer
protection from prostate cancer is still an open question. One
recent analysis that combined results from many studies found
that men who consumed the most soy foods or the isoflavones they
contain were 26 percent less likely to develop prostate cancer.
Yet studies overall suggest that men may differ in their response
to soy.
Asian populations tend to show
a much greater drop in prostate cancer risk with soy foods than
Western populations. Japanese men with highest consumption of
soy or blood levels of isoflavones have shown 40 to 60 percent
lower risk of prostate cancer than those with lowest consumption
or blood levels. Yet European studies on the effect of soy are
inconsistent.
The difference between Asian
and Western populations could stem from several sources, such
as the bacteria in our gut. All people carry millions of useful
bacteria in our digestive tract that help metabolize food, yet
different populations (and people) carry varied types of bacteria.
Some bacteria break down food isoflavones into a compound (equol)
that is linked with lower prostate cancer risk. Overall, Asian
populations show a higher proportion of equol-producers, which
could be one reason why soy is more often linked with prostate
protection in these groups.
The type of soy food also makes the research challenging. Fermentation
may change how easily our bodies absorb isoflavones, which means
that fermented soy foods (miso, tempeh, natto) may have a different
effect on prostate cancer risk than non-fermented soy foods (soy
milk, tofu and edamame). Some studies suggest that the effect
of soy foods may depend on its interaction with other food compounds;
the lycopene from tomatoes is one such interaction under study.
While we wait for more answers
about the possible protection from soy, men can feel safe eating
one or two servings of soy foods daily. Soy foods are nutritious,
low in saturated fat, and men have consumed them for generations
without harm. However, until we know more about isoflavone safety,
research does not show benefit or safety of consuming large amounts
of isoflavone supplements in hopes of achieving protection. |
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