Do the phytoestrogens in soy foods prevent cancer? Are they helpful or risky for cancer survivors? What about the estrogens in soy for men and boys?

Soy - Questions and Answers ABOUT FOODS AND CANCER PREVENTION AND SURVIVAL

QUESTION: Do the phytoestrogens in soy foods prevent cancer? Are they helpful or risky for cancer survivors? What about the estrogens in soy for men and boys?

ANSWER: Soy products, such as miso soup, tofu, and tempeh, contain very
weak plant estrogens called phytoestrogens, which block the body’s natural
estrogen from attaching to cells.27 (The prefix “phyto” simply means
“plant.”) Normally, estrogens hook onto tiny receptor proteins on your
cells that allow them to influence the cell’s chemistry.

Think of it this way: An estrogen molecule is like a jumbo jet that
attaches to the Jetway of an airport. It discharges passengers into the terminal,
which is suddenly a busy, noisy place. Phytoestrogens, being weak
estrogens, are like small, private planes with few passengers and no cargo,
yet they still occupy the Jetway after landing. When phytoestrogens occupy
the cellular receptors, normal estrogens cannot. So, while plant estrogens
do not eliminate all of estrogen’s effects, they do minimize them, apparently
reducing breast cancer risk and menstrual symptoms.28,29

Like all foods, soy products have advantages and disadvantages.
Soybeans are rich in essential omega-3 fatty acids, but they tend to be
higher in fat compared to other beans. Many soy products derive roughly
half their calories from fat, while black beans, pinto beans, or other varieties
are only about 4 percent fat. Also, soy extracts, such as genistein, may
not have the same beneficial effects as products made with the whole bean.

In Asia, where tofu, soymilk, and other soy products are commonly
consumed, not only is the population healthier overall, but cancer and
heart disease are much rarer than in North America and Europe and
longevity is greater. However, these populations differ in other ways, aside
from their use of soy products. Asians eat much less meat and dairy products
and generally exercise more compared to Americans; they also smoke
more cigarettes and eat more salt. It has therefore been difficult for
researchers to tease out the effects of soy itself.

Also, it is possible that soy products that go through more processing,
such as veggie burgers, veggie hot dogs, and particularly isolated soy protein
products, are not as beneficial as soy products with less processing,
such as whole soybeans, tofu, and tempeh, which are traditionally consumed
in Asia. Replacing processed soy products with more traditional,
less processed ones, or with other whole beans and lentils, may provide you
with a more health-promoting diet.

In human research studies, soy products have been shown to lower
blood cholesterol levels, in part due to their rich content of soluble fiber,
and their isoflavones also play a role in bone formation. Soy products have
been shown to reduce estrogen activity, at least in premenopausal women,
which, over the long run, reduces cancer risk. The evidence is not as definitive
for postmenopausal women.

Research findings are not clear on whether soy products are safe for
women who have had breast cancer. Some researchers believe that two
servings per day of soy products, such as soymilk, tofu, or tempeh, are fine
for these women, while others discourage soy consumption completely. It is
also not yet clear whether the effects of soy products differ for women with
estrogen receptor-positive breast cancer compared to those with estrogen
receptor-negative cancers.

For men and boys, the phytoestrogens in soy do not appear to have
any adverse effect on hormone levels and have not been shown to affect
sexual development or fertility.30 Research studies show that men consuming
soy have less prostate cancer and better prostate cancer survival.

However, it’s also important to remember that a vegan diet of beans,
vegetables, grains, and fruits does not have to include soy products to be
nutritionally complete. Soy products make convenient alternatives for meat
and other health-damaging foods that people, quite rightly, are looking to
avoid. However, the benefits of complete protein and soluble fiber can easily
be found in an array of plant foods.