Whether it’s being used to make vegetable oil, animal feed, tofu, soy sauce, or tempeh, the soybean has become a central crop to the US food industry, and it is becoming a larger part of the American diet. Like all big crops, soy comes with its fair share of controversies, and with “celebrity doctors” doing most of the talking to the average consumer, it has become increasingly difficult to distinguish fact from fiction. Case in point, Dr. Mercola, a Dr. Oz-esque online personality who pushes both nutritional supplements and healthy lifestyle tips, is a man who has a lot of negative things to say regarding unfermented soy products, including tofu and soymilk.

I’m a guy who has just recently gotten into using tofu as an alternative source of protein, mostly because it’s more convenient to cook and store than meat (still a sucker for that chicken parm though…). So I decided to do some research on my newfound dinner staple, and I cringed in horror at Dr. Mercola’s article on soy.

In the span of a single webpage, Dr. Mercola describes unfermented soy products as toxic, genetically modified, allergy-causing foods that contain high levels of compounds similar to estrogen. In order to support these claims, Dr. Mercola repeatedly refers to the book, “The Whole Soy Story: The Dark Side of America’s Favorite Health Food,” by Kaayla Daniel, PhD, which has a whopping 44 pages of references.

Mercola’s not the only one who has a bone to pick with soy, a men’s health article that links soy consumption to gynecomastia (aka. male breast development) tells the story of a man who drank three quarts of soymilk a day, seven days a week, and developed symptoms that are best described as “feminizing”. Yeah, you guessed it, the guy grew breasts. In addition to this real-life testimonial, Men’s Health also cites research from the journal of andrology on soy-induced erectile dysfunction in rats (yet another male impotence nightmare) to support its claim that soy is bad for reproductive health.

With both a doctor and a major magazine citing research against soy foods, I guess I should be taking my marinated tofu out of the oven and tossing it immediately into the nearest trash can, right?

Well, not exactly. Because here’s the issue with online sites that cite scientific literature to make statements about nutrition: sometimes, they blow the facts way out of proportion for readers without considering the full picture.

Remember Daniel’s book with the 44 pages of references for studies against soy? According to a review by John Robbins, author of The Food Revolution, this book was found to repeatedly either over-exaggerate or entirely dismiss the literature it was referencing in order to deliberately paint soy in a negative light. But in a sea of conflicting opinions about soy, how can we tell which one is correct? And to that, I have only one answer: SCIENCE.

The larger problem at work here is that health authorities can get away with making these claims online; they are idolized by society as “translators” of scientific knowledge and recommendations for what we should eat in order to stay healthy. Who, besides a healthcare professional, would question their doctor’s judgement when it comes to healthy lifestyle choices? And who, besides a nutritionist, would want to spend their time trying to decipher the results of largely conflicting scientific experiments performed on soy-based foods?

As a scientist in training, I decided to give it a shot: let’s put the statements of Dr. Mercola and Men’s Health under the microscope and against peer-reviewed scientific literature, to see if we can separate facts from fiction.

1) Mercola: “91% of soy grown in the US is genetically modified to be resistant to Roundup, making the soy potentially toxic.”


According to the USDA, 94% of the soybeans grown in the US in 2015 were genetically modified in a way that was potentially toxic; they were made to be herbicide tolerant against Roundup (1), a commonly used herbicide developed by Monsanto. A 2013 review of research targeting the health effects of GMO products in the Journal of Science and Healing references several studies linking herbicide sprayed soy to poisoning effects in animal studies (2).

For example, in 2009, biologist Alexey V. Surov fed GM soy to hamsters for two years across three generations, and by the third generation the hamsters were infertile(2). In yet another study, glyphosate, the active ingredient in Roundup, caused damage to the cranial cartilage of tadpoles, along with other physical alterations (3). Clearly, GM roundup-treated soy plants are not good for us, and these are the types of soy that find their way into most processed foods and cooking oils.


2) Mercola: “Soy contains soyatoxin and phytates. These are antinutrients and are harmful to humans.”

True, but they’re most likely not in the foods that we eat.

Alright, we need to stop treating animal feed like human feed, Mr. Mercola…

Soyatoxin found in raw soybean meal used for feeding animals has been shown to be highly toxic in mice (4), true, BUT I have not found any studies that show that soyatoxin is present in the soy products that humans regularly consume. If this highly toxic chemical were to be present in foods such as tofu and soymilk, there would be a lot of dead vegans.

Going along the same lines, phytates in the form of phytic acid, present in many plant tissues, have been shown to inhibit our bodies’ access to essential minerals (5). A study showed that phytates present in soybean meal lower its nutritional value (6), BUT again, organic tofu and the fermented soy products are not the same as the soybean meal used to feed animals and make unhealthy TV-dinners (7).

The consumption of raw soybeans is not recommended by healthcare professionals anyway (I’m not talking about the wonderful edamame bean, so don’t get nervous), and the toxicity of raw soybeans isn’t really a new idea (8).

Just about all of the soy products that we regularly consume are cooked versions of soybeans. Organic tofu is not made from soybean meal—rather, tofu is the curdled form of soymilk, which is made by crushing soybeans, heating them up, and separating the meal and the milk (9). Soy sauce is made through a heated fermentation process, a process which Dr. Mercola himself claims is effective in breaking down any toxins. Both of these processes involve heat, and the application of heat to soybeans (a necessary step in tofu production) has actually been shown to “practically eliminate” the toxic effects caused by soyatoxin (4).

3) Men’s Health: “The phytoestrogens genistein and daidzein cause feminizing effects in men when soy is consumed in high enough quantities.”


Let’s take a closer look at the case study of the man who developed gynecomastia—the one that this article references continuously. Genistein and daidzein are isoflavones, compounds that can have an impact on the body similar to that of the hormone estrogen. A conservative estimate for the amount of isoflavones ingested by drinking ¾ of a gallon of soymilk is 300mg/day (11). This number is more than six times the typical isoflavone consumption of older men in Japan and Shanghai, 40mg/day, so it is not surprising that a side effect consistent with excessive estrogen in the body was noticed (11). It is also worth pointing out that drinking ¾ of a gallon of regular milk every day, seven days a week, would result in dangerous levels of calcium in the bloodstream, leading to kidney stones and bone fractures (11). Isolated case studies such as this one, where isoflavone consumption is so excessive, are the exception, not the rule, to how we should look at soy.

Alright, so we shouldn’t drink a crazy amount of soymilk (or any milk really), but can these estrogen-like compounds in soy have an effect on us even when we consume normal amounts?

According to a literature review of nine human studies on the effects of isoflavones on men in The Journal of Fertility and Sterility, this is unlikely (11). Of the nine studies, only two said that the estrogen levels of subjects increased when the subjects were fed with soy protein, with a reported estrogen level increase of 20% for one study that fed subjects 6mg/day with isoflavones (12). However, the review also admits that this increase may be due to pure chance, because the studies that did not report an increase in estrogen levels fed subjects with much higher amounts of isoflavones, from 62-107mg/day (13).

As for the possibility of erectile dysfunction, an experiment in the journal of andrology has shown that exposing rats to daidzein did impair erectile function for the majority of the rats, but the dose of isoflavones was 20mg/kg for 90 days (13). With that kind of dose, of course something is going to happen!

Here’s how: if we take the average weight of a human to be roughly 55kg, the dose of daidzein needed to match that of the rat study and produce the same effects would have to be 1100mg/day! HOLY S%^#! This number is more than 20 times the standard 40mg/day isoflavone consumption for men in Japan (11), and more than three times the amount for the guy from Men’s Health who drank all that soymilk. On the whole, the effects of soy isoflavones on male hormone levels do not seem to be significant for people who do not eat a crazy amount of soy foods, and when they are significant, it is because the soy foods were consumed in crazy amounts.

The Bottom Line:

Now you’re probably thinking at this point, “Enough with the studies! Just tell me: is soy bad for me or not!?”

Having read all of this literature and gone through the giant labyrinth that is the soy nutrition debate, I definitely share your feelings. So what can we conclusively say about soy?

Well, first of all, the fact that most of the soy products produced in the US are genetically modified to be resistant to a herbicide that no human would willingly ingest is a problem, and the literature shows that some serious health issues can come as a result of GMO food consumption.

But what of the unassuming, organic soybean that was not loaded with a pesticide? In my opinion, given the studies that I have read, there’s nothing dangerous about using organic soy products as protein sources, like tofu and tempeh, or as flavoring agents, like miso and soy sauce. However, given what some of these studies have concluded regarding the toxic chemical factors present in the raw soybean meal that may creep into a lot of the processed foods and cooking oils made here in the US, I would be careful around processed foods that list soy as an ingredient. I like to keep control over what goes into my system, so I tend to just avoid processed foods entirely. With the laundry list of other chemical additives out there, this is a good idea regardless of soy’s potentially harmful qualities.


It’s hard to escape the controversy surrounding soy in the fitness community, but sometimes people blow the facts out of proportion. Sure, soy does contain isoflavones that may have some estrogenic/”womanizing” effects on men, but the examples being used to convince people that soy is a threat to their manhood use an unrealistic excess of isoflavones to produce those negative effects.

From my own experiences, I have found that the key to healthy eating is not to overreact to isolated cases (like the one shared by Men’s Health, for example) and completely cut out certain foods that may be beneficial to you; rather, you should focus on informing yourself on the foods you are eating and making smart decisions based on your own research. And as always: “everything in moderation.”

Now, if you’ll excuse me, I have some tofu to take out of the oven.

  1. Cornejo, J. F. (2015, July 09). USDA ERS - Adoption of Genetically Engineered Crops in the U.S.: Recent Trends in GE Adoption. Retrieved March 24, 2016, from http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-in-the-us/recent-trends-in-ge-adoption.aspx
  2. Schwartz, S. A. (2013). The great experiment: genetically modified organisms, scientific integrity, and national wellness. Explore: The Journal of Science and Healing, 9(1), 12-16.
  3. Paganelli, A., Gnazzo, V., Acosta, H., López, S. L., & Carrasco, A. E. (2010). Glyphosate-Based Herbicides Produce Teratogenic Effects on Vertebrates by Impairing Retinoic Acid Signaling.  Res. Toxicol. Chemical Research in Toxicology, 23(10), 1586-1595.
  4. Vasconcelos, I. M., Maia, A. A., Siebra, E. A., Oliveira, J. T., de FFU Carvalho, A., Melo, V. M., ... & Castelar, L. I. D. M. (2001). Nutritional study of two Brazilian soybean (Glycine max) cultivars differing in the contents of antinutritional and toxic proteins. The Journal of nutritional biochemistry,12(1), 55-62.
  5. Cheryan, M., & Rackis, J. J. (1980). Phytic acid interactions in food systems. Critical Reviews in Food Science & Nutrition, 13(4), 297-335.
  6. Soybean bioactive components and their implications to health—a review. Food reviews international, 24(2), 252-276.
  7. Egounlety, M., & Aworh, O. C. (2003). Effect of soaking, dehulling, cooking and fermentation with Rhizopus oligosporus on the oligosaccharides, trypsin inhibitor, phytic acid and tannins of soybean (Glycine max Merr.), cowpea (Vigna unguiculata L. Walp) and groundbean (Macrotyloma geocarpa Harms).Journal of Food Engineering, 56(2), 249-254.
  8. Perkins, S. (n.d.). What Happens if You Eat Raw Soybeans? Retrieved April 04, 2016, from http://healthyeating.sfgate.com/happens-eat-raw-soybeans-11856.html
  9. Ever wonder how Tofu is made? - Amy's Kitchen - We Love To Cook For You™. (n.d.). Retrieved April 04, 2016, from http://www.amys.com/about-us/our-kitchen/ever-wonder-how-tofu-is-made
  10. , S. (2013). Soybean, Nutrition and Health. Soybean - Bio-Active Compounds.
  11. Messina, M. (2010). Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence.Fertility and sterility, 93(7), 2095-2104.
  12. Hamilton-Reeves JM, Rebello SA, Thomas W, Slaton JW, Kurzer MS. Isoflavone-rich soy protein isolate suppresses androgen receptor expression without altering estrogen receptor-{beta} expression or serum hormonal profiles in men at high risk of prostate cancer. J Nutr 2007;137:1769–75.
  13. Huang Y, Pan L, Xia X, Feng Y, Jiang C, Cui Y. Long-term effects of phytoestrogen daidzein on penile cavernosal structures in adult rats. Urology 2008;72:220–4.

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