Soy and Your Health
Dr. Neal Barnard
Soybeans are handy. Aside from the traditional foods they bring us --
edamame, tofu, tempeh, and many others -- they transform into tasty
substitutes for milk, yogurt, ice cream, bacon, burgers, and sausage.
With no animal fat, cholesterol, or sensitizing animal proteins, they
side-step the problems that animal products can cause. Cow's milk, for
example, is linked to Type 1 diabetes and anemia in children and
increases the risk of prostate cancer in men. Hamburgers are linked to
heart disease, diabetes, and colon cancer. Soy-based milks and burgers
help you skip all this. But soy has other huge benefits you may not know
Soy Products Reduce Cancer Risk
In the 1930s, researchers discovered that soybeans and other
legumes contain natural isoflavones, compounds that appeared to have
an anticancer effect.
However, their chemical structure was similar to human estrogens.
Compare the molecular structure of genistein, a common soy isoflavone,
with that of estradiol, the most abundant human estrogen in women
during their reproductive years. So some people wondered whether soy
products might have hormonal effects -- feminizing men or increasing
cancer risk in women, for example.
Researchers put these concerns to the test. The results of human
studies clearly show no negative effect at all on men's hormonal
function, testosterone levels, or sperm count.,
As for breast cancer, it turns out that soy has a preventive
effect. Researchers from the University of Southern California
compiled the results of eight prior studies, finding that women who
have a cup of soymilk or a half-cup of tofu each day have about a 30
percent reduced risk of developing breast cancer, compared with women
who consume little or no soy.
Soy Products Boost Survival in Breast Cancer Patients
Some doctors have advised women with breast cancer to avoid
soy-based products on the notion that soy is similar to estrogens.
However, studies have shown that soy is actually a boon to cancer
survivors. In 2012, the American Journal of Clinical Nutrition
published a report compiling the findings of three separate studies in
the U.S. and China, including the experiences of 9,514 breast cancer
survivors. It showed that, among women with a history of breast
cancer, regular consumption of at least a modest amount of soy
products cut the risk of recurrence by 25 percent.
So, soy products don't increase cancer risk; they reduce it. And
they boost survival odds for women previously diagnosed with cancer.
Soy Products Lower Cholesterol. First of all, soy products replace
cholesterol-laden sausage, bacon, and burgers. But soy protein
directly lowers blood cholesterol.
Soy skeptics -- and the dairy industry -- are fond of attacking soy
products. Here is what you need to know about the issues they raise:
GMO foods: They are easy to avoid. Genetically
modified products may be a cause for concern. But people who buy soy
products find it easy to avoid them. Just look for the word "organic"
on soymilk, tofu, and other foods. By law, they cannot be GMO. Who
needs to worry? GMO soy products are fed to cattle and other animals
on a daily basis, so it's meat-eaters who should be concerned.
Thyroid Health: Soy products do not affect it. Soy
products do not cause thyroid problems in people with normal
functioning thyroids. However, if you are taking medications for an
underactive thyroid, you should be aware that many foods, including
soy products, can reduce the absorption of medications, including
thyroid supplements. Your doctor will periodically check to see if
your dose needs to be adjusted.
Minerals: They are well-absorbed. Phytate is a
natural compound found in legumes and whole grains, and some people
have pointed out that it reduces mineral absorption. However, clinical
studies show that calcium in typical calcium-fortified soymilk and
tofu products made with calcium is absorbed as well as calcium from
cow's milk. Also, research suggests that the iron in soy products is
Protein: It is well-digested. Some writers have
suggested that protease inhibitors in beans, including soy, reduce
protein absorption. However, studies show that soy protein is, in
fact, highly digestible.
Fermented or unfermented soy: They are both fine.
Some have suggested that the good health many Asians enjoy is due to
their choice of fermented soy products (eg, miso or tempeh), rather
than unfermented products (tofu and soymilk). However, in Japan, about
half of soy products consumed are unfermented (mainly tofu). In China,
Hong Kong, and Singapore, nearly all is unfermented foods (tofu and
Having said all of this, soy products are strictly optional. A
healthy vegan diet could be based on a Mediterranean tradition,
emphasizing vegetables, fruits, chickpeas, and pasta. It could be
based on Latin American tastes, with plenty of beans, tortillas, and
fresh fruit. Soy products come from the traditions of Asian countries
where people are generally thinner and healthier and live longer than
Americans. But soy is still entirely optional.
However, if you are not a soy fan, the worst thing to do is to
retreat to meat or dairy products. Omnivorous children and adults have
a higher risk of many health problems, compared to their vegetarian
friends. Whether you replace animal products with beans, vegetables,
fruits, whole grains, or soy products, you're doing your body a favor.
1. Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. Clinical studies
show no effects of soy protein or isoflavones on reproductive hormones
in men: results of a meta-analysis. Fertil Steril 2010;94:997-1007.
2. Messina M. Soybean isoflavone exposure does not have feminizing
effects on men: a critical examination of the clinical evidence.
Fertil Steril 2010;93:2095-104. (see attached PDF)
3. Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures
and breast cancer risk. Br J Cancer 2008;98:9-14. Wu AH, Yu MC, Tseng
CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br
J Cancer 2008;98:9-14.
4. Nechuta SJ, Caan BJ, Chen WY, et al. Soy food intake after
diagnosis of breast cancer and survival: an in-depth analysis of
combined evidence from cohort studies of US and Chinese women. Am J
Clin Nutr. 2012;96:123-32.
5. Messina M. Redmond G. Effects of soy protein and soybean
isoflavones on thyroid function in healthy adults and hypothyroid
patients: a review of the relevant literature. Thyroid.
Neal D. Barnard, M.D., is an Adjunct Associate Professor of
Medicine at the George Washington University School of Medicine and
President of the Physicians Committee for Responsible Medicine in
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