You hear so many things about soy products now days, it gets confusing. I
found this article that explains and agrees with a lot other articles I
have read, this one is from Dr. Neal Barnard.
If you buy soy products, look for organic products and as with everything, moderation is the key.
Soy products are remarkably versatile. Manufacturers have found
ways to turn them into soymilk, veggie burgers, hot dogs, ice cream,
yogurt--you name it. One day, they'll probably turn soy into snow tires.
Because soy products are so widely consumed, some people have raised
the question as to whether they are safe. The biggest question mark was
whether they affect the risk of breast cancer and, for women who have
been diagnosed with breast cancer, whether they would help or harm their
chances for survival.
After years of research, science is weighing in. Here is what the studies show:
Cancer Prevention and Survival
Women who include soy products in their routines are less likely to
develop breast cancer, compared with other women. In January 2008,
researchers at the University of Southern California found that women
averaging one cup of soymilk or about one-half cup of tofu daily have
about a 30 percent less risk of developing breast cancer, compared with
women who have little or no soy products in their diets (1). However, to
be effective, the soy consumption may have to occur early in life, as
breast tissue is forming during adolescence (2-3).
What about women who have already been diagnosed with breast cancer? A study published in the Journal of the American Medical Association
in 2009 shows that soy products may reduce the risk of recurrence (4).
In a group of 5,042 women previously diagnosed with breast cancer who
were participating in the Shanghai Breast Cancer Survival Study over a
four-year period, those who regularly consumed soy products, such as
soymilk, tofu, or edamame, had a 32 percent lower risk of recurrence and
a 29 percent decreased risk of death, compared with women who consumed
little or no soy. An accompanying editorial suggested that
inconsistencies in prior research may be attributable to the
comparatively low soy consumption in the United States, making
beneficial effects harder to identify (5).
Why should soy products reduce cancer risk? Most research has zeroed
in on phytoestrogens found in soybeans (phyto means "plant"). These
compounds are in some ways similar to the estrogens (female sex
hormones) in a woman's bloodstream, but are much weaker. Some have
suggested that phytoestrogens attach to the estrogen receptors in a
woman's body, blocking her natural estrogens from being able to attach
and stopping estrogen's cancer-inducing effects.
By analogy, the estrogens in a woman's body are like jumbo jets that
have landed at an airport. Phytoestrogens are like small private planes
that are occupying the Jetways, blocking the jumbo jets from attaching.
This explanation is probably overly simplistic, but it may serve to
illustrate how soy's weak hormonal compounds can have beneficial
effects.
Fibroids
Soy products may reduce the risk of fibroids, knots of muscle tissue
that form within the thin muscle layer that lies beneath the uterine
lining. A study of Japanese women found that the more soy women ate, the
less likely they were to need a hysterectomy, suggesting that fibroids
were less frequent (6). In a study of women in Washington State, soy did
not seem to help or hurt, perhaps because American women eat very
little soy, compared with their Japanese counterparts (7). What did have
a big effect in this study were lignans, a type of phytoestrogens found
in flaxseed and whole grains. The women consuming the highest amounts
of these foods has less than half the risk of fibroids, compared with
the women who generally skipped these foods. So, again, phytoestrogens
seem beneficial, countering the effects of a woman's natural estrogens,
although in this case the benefit comes from foods other than soy.
Soy and Male Hormones
How about men? Although compounds in soy products have been likened
to very weak female hormones, they have no adverse effects on men and
may actually help them prevent cancer. A meta-analysis to be published
in Fertility and Sterility, based on more than 50 treatment
groups, showed that neither soy foods nor isoflavone supplements from
soy affect testosterone levels in men (8). An analysis of 14 studies,
published in the American Journal of Clinical Nutrition showed
that increased intake of soy resulted in a 26 percent reduction in
prostate cancer risk (9). Researchers found a 30 percent risk reduction
with nonfermented soy products such as soy milk and tofu.
Thyroid Health
Clinical studies show that soy products do not cause hypothyroidism (10). However,
soy isoflavones may take up some of the iodine that the body would
normally use to make thyroid hormone (11). The same is true of fiber
supplements and some medications. In theory, then, people who consume
soy might need slightly more iodine in their diets (iodine is found in
many plant foods, and especially in seaweed and iodized salt.) Also, a
note for people with hypothyroidism: Soy products may reduce the
absorption of medicines used to treat the condition (10). People who use
these medicines should check with their healthcare providers to see if
their doses need to be adjusted.
Other Health Effects
Soy products appear to reduce low density lipoprotein ("bad")
cholesterol (12). They may also reduce the risk of osteoporosis-related
hip fractures. In a study published in the American Journal of Epidemiology, women who consumed at least one-fourth cup of tofu per day averaged a 30 percent reduction in fracture risk (13).
Protein: A Little Goes a Long Way
Many soy products are high in protein. Manufacturers have exploited
this fact, packing isolated soy protein into shakes and turning it into
meat substitutes. But some have raised the concern that pushing protein
intake too high--from any source--might not be wise. The concern is that
an overly high protein intake may boost the amount of insulin-like
growth factor (IGF-I) in the bloodstream (14), a phenomenon known to
occur with cow's milk (15). High IGF-I levels are linked to higher
cancer risk. Some reassurance comes from the fact that soy intake is
linked to lower, not higher, cancer risk, and simple soy products, such
as tempeh, edamame, or soynuts, are unlikely to affect IGF-I levels, in
any case.
In summary, evidence to date is reassuring. Soy products may reduce
the risk of breast cancer and breast cancer recurrence. They do not
appear to have adverse effects on male hormone function or on the
thyroid gland, but may reduce the absorption of thyroid medications.
Having said that, soy products are certainly not essential. Many
people who start a healthful vegan diet, as I and many other doctors
recommend, seem to feel they must have soy products. But the fact is, a
vegan diet can follow a Mediterranean tradition, focusing on vegetables,
fruits, beans and pasta. Or it might follow a Latin American tradition
of beans, rice, and corn tortillas. Soy products come from an Asian
tradition with many healthful delights and the most enviable health
statistics on record. So soy is handy, but it is certainly not
essential. If you choose to include soy products in your routine, you'll
have science on your side.
http://www.huffingtonpost.com/neal-barnard-md/settling-the-soy-controve_b_453966.html
