Is Soy Healthy For Men?

Soy is not a miracle product, no matter what the food producers and marketing people tell you. Nor, however, is it a dangerous substance you should avoid at all costs. Although research indicates there are plenty of reasons to be concerned about soy, there also is science showing some very positive things. So what’s wrong and right with soy?

The challenge is to distinguish between the hype and the science—which itself is not always easy to decipher—and decide what is wrong and right with soy and soy foods for you, your health, and your lifestyle.

Soy in America: A Very Brief History

Soy and soybean products made an inconspicuous entrance into the US market in the late 1970s, when the Hong Kong-based soy-milk producer Vitasoy introduced its product to Americans. Gradually over the next decade, other soyfood companies, mainly small family-owned companies, joined in. As advances in food processing developed, they allowed manufacturers to make soy foods from soybean components such as soy protein concentrates and soy protein isolates.

Suddenly soymilk was joined by a variety of other soy-based foods (e.g., soy hot dogs, soy burgers, soy cheese) as well as a surge in the number of mainstream foods that now had soy protein concentrates and isolates as ingredients. The advances in food technology triggered a burst of activity in the 1990s as soyfoods and foods containing soy were marketed as providing a number of health benefits, ranging from lowering cholesterol to eliminating hot flashes and protecting against breast and prostate cancer. The problem, however, was that these claims were generally premature, inaccurate, and/or not well substantiated.

Approximately 20 years later, there are still debates and controversies about the validity of health claims and warnings regarding soy and soy foods. In recent years, the topic has been complicated by the introduction of genetically modified (GM) soybeans, which introduces new concerns about health and safety.

Something that goes along with GM soybeans is an excessively high level of pesticides: because GM soybeans are designed to resist pesticides, they can be treated with high levels of these toxins, which in turn can harbor themselves in the crop.  In fact, 90 to 95 percent of the soybeans produced in the United States are genetically modified. In the midst of all these concerns, the research continues. Here is some of what is known thus far.

What about Soy Protein Concentrate and Isolates?

If you pick up a loaf of bread, protein bar, can of soup, breakfast cereal, meal replacement bars or shakes, canned or bottled fruit drink, or jar of pasta sauce, you will likely see the words “soy protein isolate” or “soy protein concentrate” listed on the ingredient panel. The Soyfoods Association of North America states that “soy protein isolate is a dry powder food ingredient that has been separated or isolated from the other components of the soybean, making it 90 to 95 percent protein and nearly carbohydrate and fat-free.”

On the surface, this explanation does not seem threatening. After all, a very high protein food product that is nearly fat-free sounds like a healthy product. This is the information food producers and marketers use, along with the health claims already mentioned, to promote the use of soy and soy-based foods.

However, soy and soy protein isolates have been associated with a variety of health problems, which I address below. One major issue with soy protein isolates is how it is produced: the soybeans are washed in acid in aluminum tanks, which leeches aluminum into the protein isolates. Aluminum can have negative effects on the brain, and has been linked to dementia, antisocial behavior, and learning disabilities.

Other Names for Soy Protein

Soy and soy additives can appear in your food under a variety of different names, so if you are trying to limit or avoid soy, it’s important for you to recognize the possible aliases. They are “possible” aliases because soy is not always the basis of all of these ingredients, which is why you need to contact the manufacturer to ask about the source. Lecithin, for example, can be made from corn, eggs, soy, or sunflower. Some soy aliases can include: boullion, natural flavor, textured plant protein, textured soy flour, kinako, lecithin, monosodium glutamate, mono-diglyceride, soya, soja, and yuba.

Avoid Genetically Modified Soy

Genetically modified soybeans have been chemically engineered with a bacterial gene that allows the soybean plants to resist otherwise deadly doses of herbicides, specifically Roundup, the most widely used herbicide in the world. The active ingredient in this product, called glyphosate, has a systemic effect, which means it penetrates the crop and cannot be completely removed from food by peeling, washing, or processing. Therefore glyphosate accumulates in the beans, which are then consumed by humans as well as by food animals. This means you have a double chance of exposure to herbicides.

Research shows that glyphosate, especially when it is applied with the other ingredients in Roundup, can disrupt aromatase, a substance that is necessary for luteal cells to produce estrogen for a normal menstrual cycle. In rats fed genetically modified soybeans, the luteal cells have been altered. (Benachour 2009) Glyphosate can also impair the placenta, which is critical for the health of the fetus.

Soy and Its Isoflavones

Soy contains phytochemicals called isoflavones—specifically genistein and daidzein—that mimic hormones and can disrupt the hormone balance in the body. Some limited research indicates these two phytoestrogens may have an impact on a man’s libido and erectile function. A study conducted in juvenile rats found that daidzein impaired erectile function in the animals (Pan 2008), and there was an unusual case of a 60-year-old man who developed enlarged breasts as a result of consuming high amounts of soy. (Martinez 2008)

However, a meta-analysis conducted at the University of Loma Linda in California and published in 2010 reported that soybean isoflavones do not have a feminizing effect on men. The investigators evaluated both animal and human clinical studies and found that neither isoflavone supplements nor isoflavone-rich soy had an effect on testosterone levels, circulating estrogen levels, or sperm parameters.  The researchers also concluded that animal studies suggesting isoflavones can increase the risk of erectile dysfunction are not applicable to men because there is a difference in isoflavone metabolism between rodents and humans. (Messina 2010)

One of the arguments often used to support the consumption of soy and soy foods is that Asians, who make soy a regular part of their diet, have a lower risk of hormone-related cancers, including breast, prostate, and uterine cancers. At the same time, some individuals use the argument that Asians are at higher risk of developing other types of cancer, including cancer of the esophagus, liver, pancreas, stomach, and thyroid.

The higher rate of these cancers among Asians has not been directly linked to soy consumption, however. In fact, a recent study pointed out an association between alcohol consumption, cigarette smoking, and esophageal cancer among East Asians. (Yokoyama 2010) Several epidemiological studies suggest that eating soybeans may contribute not only to a lower incidence of breast and prostate cancers, but also thyroid, colon, head, and neck cancers, and genistein is named as the providing the protective effect. (Horn-Ross, 2002; Radzikowski 2004) Some animal studies, however, have shown a higher risk of these cancers when rodents were fed a soy diet.

In addition to acting as hormone mimics, the isoflavones in both fermented and unfermented soy also can have an impact on thyroid function. When soy isoflavones act as goitrogens, they can disrupt your thyroid, resulting in symptoms such as anxiety, digestive problems, food allergies, insomnia, mood swings, and trouble losing weight.

Fermented Soy, the Healthy Choice

An important fact to note about the soy Asians eat is that some of it is fermented soy, which is the only type of soy that provides health benefits. In fact, the ancient Chinese did not consider soybeans as food until they discovered fermentation. Unlike fermentation, regular cooking of soybeans does not destroy enzyme inhibitors, which can produce serious gastrointestinal distress, reduce the ability to digest protein, and lead to chronic deficiencies in the uptake of amino acids.

Fermented soy foods (see below) are the result of the activity of bacteria on soybeans. Fermented soy has several important benefits. For example, fermentation stops the effect of a substance called phytic acid, which causes the elimination of vital nutrients from the body. Phytic acid also blocks the utilization of essential minerals such as calcium, copper, iron, magnesium, and zinc. Therefore, you risk a deficiency of important nutrients and minerals when you consume unfermented soy products.

Fermented Soy Foods Include:

Miso, a salty, fermented soybean paste that is often used to make miso soup and as seasoning

Natto, fermented soybeans available in a cake-like form and having a cheesy flavor and sticky texture

Soy sauce, made by fermenting soybeans, enzymes, and salt. Look for varieties made using natural fermentation and not a chemical process

Tempeh, a fermented soybean food formed into a firm, flat cake form and possessing a nutty, mushroom-like flavor

Fermentation also bestows other health benefits on soy. One, it creates good bacteria called probiotics, which increase the availability, assimilation, digestibility, and quantity of nutrients in the body. Two, fermented soy foods are a rich source of vitamin K2, a vitamin that is important in helping blood clot and in preventing cancer, osteoporosis, and heart disease.

Unfermented Soy and Vegetarians

Vegetarians who consume unfermented soy foods such as soy milk and soy burgers that contain soy protein isolate (probably genetically modified) as their primary protein sources may be at risk for nutrient deficiencies associated with phytic acid. If this describes you, it would be wise to include other non-animal sources of protein in your diet, such as beans, lentils, split peas, nuts, flaxseeds, hemp seeds, and protein-rich grains such as buckwheat, kamut, and quinoa. Healthful alternatives to soymilk (especially if you are lactose intolerance) include almond milk and hemp milk.

Soy For Babies and Children

Some experts warn against giving babies soy infant formula because it exposes the children to excessively high levels of isoflavones, specifically genistein. According to the draft findings of the National Toxicology Program (NTP) issued in March 2010, “blood levels of total genistein in infants fed a soy infant formula diet can exceed those reported in young rats or mice treated with genistein during development at dose levels that produced adverse effects, i.e., early onset of sexual maturation, altered estrous cyclicity and decreased litter size.” (National Toxicology Program)

The authors of the NTP point out, however, that these types of adverse effects have not been reported in babies throughout the 60 years soy infant formula has been available. The lack of reports is associated with the fact that no adequate studies of the reproductive system in females have been conducted following use of soy infant formula during infancy. Therefore the authors rated the level of concern 2 out of 5 and concluded that data in humans are insufficient to dismiss the possibility of subtle or long-term adverse effects in infants who consume soy formula.

In addition to the possible side effects seen in animal studies, some other adverse effects in children could include behavioral problems, food allergies, digestive problems, asthma, cancer, and thyroid disease. Soy formula may also contain toxins such as aluminum and manganese, which have been linked to physical and mental problems, such as brain damage, behavioral problems, and learning disabilities. Some experts have expressed concern over the fact that according to US government standards, soy products are now being added to foods in school lunches, which may have the potential to deplete necessary nutrients and contribute to learning disabilities.

The Bottom Line

If you want to include soy in your diet, fermented soy and soy foods are the healthiest choice, and always look for those made from non-genetically modified soybeans. Read labels carefully and avoid foods that have soy protein isolates as an ingredient, which includes soy protein bars, protein powders for athletes and bodybuilders, and a wide variety of foods on supermarket shelves.


Benachour N, Seralini G-E. Glyphosate formulations induce apoptosis and necrosis in human umbilical, embryonic, and placental cells. Chemical Research in Toxicology 2009; 22(1): 97-105

Horn-Ross PL et al. Phytoestrogens and thyroid cancer risk: the San Francisco Bay Area thyroid cancer study. Cancer Epidemiol Biomarkers Prev 2002 Jan; 11(1): 43-49

Martinez J, Lewi JE. An unusual case of gynecomastia associated with soy product consumption. Endocr Pract 2008 May-Jun; 14(4): 415-18

Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril 2010 May 1:93(7): 2095-104

National Toxicology Program: Draft NTP brief on soy infant formula.

Pan L et al. Exposure of juvenile rats to the phytoestrogen daidzein impairs erectile function in a dose-related manner in adulthood. J Androl 2008 Jan-Feb; 29(1): 55-62

Radzikowski C et al. Genistein: a soy isoflavone revealing a pleiotropic mechanism of action—clinical implications in the treatment and prevention of cancer. Postepv Hig Med Dosw 2004 Feb 27; 58:128-39

Soyfoods Association of North America. History of soy products

Yokoyama A et al. Alcohol and aldehyde dehydrogenase polymorphisms and a new strategy for prevention and screening for cancer in the upper aerodigestive tract in East Asians. Keio J Med 2010 Dec; 59(4): 115-30

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