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Soy: Healthy Or Harmful?

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It's one of our biggest national crops. Vegetarians abide by its alternative protein source. And it is central to much of Japanese food -- considered one of the healthiest cuisines in the world.

But while some laud the soy bean as a cheap, low-fat, cholesterol-free source of high quality protein, detractors point to some evidence that foods made from soy could cause harm. What kind of harm? Research in mice shows that a compound in soy can mimic the hormone estrogen and scientists extrapolate that this compound could be disrupting childhood development, rising the risk of cancer and contributing to infertility.

Is that enough to go on? We invited two leading experts to weigh in.


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Soy is a healthful food.

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Who makes the better argument?

Neal Barnard, M.D. President, Physicians Committee for Responsible Medicine

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 about.

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.

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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.[1],[2]

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.[3]

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.[4] 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.[5] 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 well absorbed.

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 soymilk).

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. 2006;16:249-58.

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 Washington, DC.

For more by Neal Barnard, M.D., click here.

For more on diet and nutrition, click here.

Dr. Joseph Mercola Physician and author

Who hasn't heard of the marvels of soy? The marketing bandwagon has touted soy as the perfect health food for decades. But could something that sounds so healthful actually be dangerous?

If you take the time to look into the actual science, then the answer is yes. Thousands of studies link soy to malnutrition, digestive distress, immune system breakdown, thyroid dysfunction, cognitive decline, reproductive disorders and infertility -- even cancer and heart disease.

One of the primary reasons it would be wise for you to avoid soy is that more than 90 percent of soybeans grown in the United States are genetically modified. Since the introduction of genetically engineered foods in 1996, we've had an upsurge in low birth weight babies, infertility, and other problems in the U.S., and animal studies have shown devastating effects from genetically engineered soy including allergies, sterility, birth defects, and offspring death rates up to five times higher than normal.

Soybean crops are also heavily sprayed with chemical herbicides, such glyphosate, which a French team of researchers have found to be carcinogenic.

Soybeans -- even organically grown soybeans -- naturally contain "antinutrients" such as saponins, soyatoxin, phytates, trypsin inhibitors, goitrogens and phytoestrogens. Traditional fermentation destroys these antinutrients, which allows your body to enjoy soy's nutritional benefits. However, most Westerners do not consume fermented soy, but rather unfermented soy, mostly in the form of soymilk, tofu, TVP, and soy infant formula.

Unfermented soy has the following 10 adverse affects on your body:

1. High Phytic Acid (Phytates): Reduces assimilation of calcium, magnesium, copper, iron and zinc. Phytic acid in soy is not neutralized by ordinary preparation methods such as soaking, sprouting and long, slow cooking, but only with long fermentation. High-phytate diets have caused growth problems in children.

2. Trypsin inhibitors: Interferes with protein digestion and may cause pancreatic disorders. In test animals, trypsin inhibitors in soy caused stunted growth.

3. Goitrogens: Potent agents that block your synthesis of thyroid hormones and can cause hypothyroidism and thyroid cancer. In infants, consumption of soy formula has been linked with autoimmune thyroid disease. Goitrogens interfere with iodine metabolism.

4. Phytoestrogens/Isoflavones: Plant compounds resembling human estrogen can block your normal estrogen and disrupt endocrine function, cause infertility, and increase your risk for breast cancer.

5. Hemagglutinin: A clot-promoting substance that causes your red blood cells to clump, making them unable to properly absorb and distribute oxygen to your tissues.

6. Synthetic Vitamin D: Soy foods increase your body's vitamin D requirement, which is why companies add synthetic vitamin D2 to soymilk (a toxic form of vitamin D).

7. Vitamin B12: Soy contains a compound resembling vitamin B12 that cannot be used by your body, so soy foods can actually contribute to B12 deficiency, especially among vegans.

8. Protein Denaturing: Fragile proteins are denatured during high temperature processing to make soy protein isolate and textured vegetable protein (TVP). Chemical processing of soy protein results in the formation of toxic lysinoalanine and highly carcinogenic nitrosamines.

9. MSG: Free glutamic acid, or MSG, is a potent neurotoxin. MSG is formed during soy food processing, plus additional MSG is often added to mask soy's unpleasant taste.

10. Aluminum and Manganese: Soy foods contain high levels of aluminum, which is toxic to your nervous system and kidneys, and manganese, which wreaks havoc on your baby's immature metabolic system.

Soy's antinutrients are quite potent. Drinking just two glasses of soymilk daily provides enough of these compounds to alter a woman's menstrual cycle. But if you feed soy to your infant or child, these effects are magnified a thousand-fold. Infants fed soy formula may have up to 20,000 times more estrogen circulating through their bodies as those fed other formulas. You should NEVER feed your infant a soy-based formula!

In fact, infants fed soy formula take in an estimated five birth control pills' worth of estrogen every day.

As dangerous as unfermented soy is, fermented soy from organic soybeans is a different story altogether and can be a beneficial part of your diet. Fermented soy is a great source of vitamin K2, and K2 (combined with vitamin D) is essential in preventing osteoporosis, cardiovascular disease, dementia, and various types of cancer.

Note that tofu is NOT on this list and is among the soy foods I do not recommend. Traditionally fermented soy products include:

  • Miso
  • Tempeh
  • Natto
  • Soy sauce (as long as it's fermented in the traditional way, and not all are)

Contrary to what you may have heard, Asians do not consume large amounts of soy. They use small amounts as a condiment (about two teaspoons daily), but not as a primary protein source. And the type of soy they consume is traditionally fermented soy.

For more information about the health problems you may confront related to dietary soy, I invite you to download my free comprehensive soy report.

For more by Dr. Joseph Mercola, click here.

For more on diet and nutrition, click here.



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