It is now
clear that soy intake during adolescence, a time when breast tissue is most
sensitive to environmental stimuli and
carcinogenesis, may reduce the risk of breast
cancer later in life. Recent articles in Cancer Epidemiology and
The American Journal of Clinical Nutrition reported that soy consumption during childhood
and teenage years reduced the risk of
breast cancer in adulthood
by 60 percent and 40 percent, respectively.
Soybeans are rich in
isoflavones, a type of phytoestrogen. Phytoestrogens are plant substances
that are chemically similar to estrogen and since higher
estrogen levels promote breast cancer, some people predicted that soy would too. Now we
know that the phytoestrogens in soy actually
block the effects of the body's estrogen. Despite myths propagated on the Internet, the most
recent and reliable clinical studies support a strong protective
effect of minimally processed soy foods against breast
cancer.
In 2006, a meta-analysis in the Journal of the National Cancer Institute examining data from eighteen studies on soy and breast cancer that were published between 1978 and 2004 concluded that soy overall has a protective effect. Again in 2008, another meta-analysis in the British Journal of Nutrition compiling data from eight studies (which were not included in the 2006 meta-analysis) also concluded that soy consumption decreases breast cancer risk. These effects were dose-dependent - a 16 percent reduced risk for each 10 milligrams of soy isoflavones consumed daily.
Soy has protective effects even after a diagnosis of breast cancer.
A new study of breast cancer survivors has shown that premenopausal breast cancer
survivors who consumed more soy had a 23 percent reduced risk of recurrence.
Soy provides protection against other hormonal cancers as well.
A meta-analysis of studies on soy consumption and prostate cancer found a 31 percent
decrease in prostate cancer risk with a high consumption of soy foods.
Soy has also been shown to be protective against endometrial
and ovarian cancers. Soy products such as tofu and soy milk can be useful in moving
toward a plant-centered diet with less saturated fat, less animal protein, more
plant protein, and more fruits and vegetables. In the United States, the majority
of our soy intake, which is very low compared to that of Asian countries, is consumed
via soy-based additives or isolated soy protein in processed foods.
Please note that the most healthful soy foods are those that
are minimally processed - these include edamame, tofu, unsweetened soy milk,
and tempeh. You should be aware that soy nuts and other processed soy products do
not retain much of the beneficial compounds and omega-3 fats that are in the natural
bean. The more the food is processed, the more these beneficial compounds are destroyed.
Minimally processed soy foods are a beneficial addition to a healthy diet. I do
not recommend consuming large quantities of soy products in the hopes of reducing
cancer risk, however. A healthy diet should include a variety of beans, all of
which have beneficial anticancer compounds, and not a disproportionate share of
calories from soy. I always recommend the consumption of a broad variety of phytochemical-rich
foods to maximize one's health. Beans are no exception - try to include various
different types of beans, including soybeans.
Processed foods, because of their low nutrient levels, high
amounts of salt, acrylamides, and other toxic additives, should not be considered
healthy. Vegetarians and vegans who eat tofu-turkey, soy burgers, soy ice cream,
soy hotdogs, soy cheese and other soy-derived processed foods on a regular
basis are certainly not eating a healthy diet. Isolated soy protein is a heavily
processed food with the natural micronutrients lost in processing. The key to good
health is to eat unprocessed foods, because their nutrient-per-calorie
density is high.
(Joel Fuhrman, M.D., ‘Super
Immunity’)