Soy has quickly gone from a relatively unknown in Western culture to a highly debated and controversial food. Of course, soy has not been embraced by communities who have been advocating against grain and legume consumption for decades.
Even people who eat predominately plant-based diets will campaign against this humble legume. The question is: are these harsh criticisms warranted or does the scientific literature say otherwise?
Introduction on Soy
A flurry of blog posts, most without any or with limited sources from scientific literature, has emerged attempting to prove once and for all how dangerous soy consumption is for human health.
Claims can range anywhere from “soy causes breast cancer and increases estrogen levels” to “phytates in soy leeches nutrients from your body”.
In this post, we will closely examine common objections against soy. We will explore the truths many online resources got right and the falsehoods that many got wrong.
We will dive deep into the actual scientific research behind soy consumption and ultimately be able to conclude soy, when consumed in any reasonable amount, protects against disease and promotes overall health.
**Please note that this article is about whole-foods plant based sources of soy, not soy additives in processed foods.
Debunking Anti-Soy Claims
- Soy is the least common of all food allergens.
- You're much more likely to be allergic to fish, eggs, shellfish, nuts, wheat, or peanuts.
To start, yes there are some people who shouldn’t eat soy. Some people do have allergies to soy, but it is actually the least common of all the main allergens.
A national survey found that 1 in 2,000 people have a soy allergy. For comparison, this is 40 times less likely than dairy, and 10 times less than fish, eggs, shellfish, nuts, wheat, or peanuts. 
What About GMO Soy?
- Majority of GMO soy grown is for the purpose of feeding animals.
- Consuming factory farmed (and even pasture-raised animals in some cases) means you're consuming GMO soy second-hand.
- The immediate danger comes in the pesticides being sprayed on the soy. Genetic modification needs to be tested long-term and should be labeled.
- Buying organic soy products is the easiest way to avoid the dangers of GMO soy.
Concerning GMOs, there certainly has not been enough testing done on the long-term effects of these foods, and they should be, at-best, labelled so each consumer has the right to know what they’re eating.
The main issue with GMO soy may not necessarily be the modification, but the actual Roundup being sprayed in large doses on these crops. This substance has been proven to product toxic and hormonal effects at even lower concentrations than what’s used on crops. 
More Details on GMO Soy by
If you’ve been avoiding soy because you think it’s either unhealthy, GMO, or similar, there is an unfortunate dilemma. 90% of the soy production in the world goes to animal feed and given to cows, chickens, and pigs. If you’re eating any of these animals and fearful of the dangers of soy, you’re still consuming it second-hand. 
The main soy used for for humans manufacturers use Non-GMO soy, but we recommend buying organic soy products just to be safe.
Is Soy Environmentally Destructive?
- Most soy is grown to feed animals for slaughter, not humans.
- Livestock systems are far more unsustainable than growing soy to feed humans.
- By consuming factory farmed animal products, you're indirectly consuming GMO-soy in much greater quantities.
- Grass-fed animal products may still be fed soy/grain and are much more unsustainable.
- Organic soy products are an environmentally safe option.
Soy gets a lot of flak for being a crop that is environmentally destructive. However, the brunt of this issue falls upon consumers of animal products and the animal agriculture industry, not soy itself. As stated above, the majority of GMO soy is grown for the sole purpose of feeding animals.
Of course, there are the grass-fed free, range animal options, which may not be fed with soy. Even "grass-fed" options, though, may be fed grain during a portion of the year during the end of their lives to fatten them up before slaughter . It’s also completely unsustainable for the environment. Livestock systems already cover 45% of the earth’s total landmass and cattle ranching is responsible for 91% of Amazonian rainforest destruction. 
These are huge numbers, and our limited land resources will only decrease as the demand for grass-fed meat increases. One grass-fed cow takes 9 acres of land to raise, whereas a grain-fed cow takes 3 acres. We simply don’t have enough land for everyone to eat grass-fed animals. 
With the majority of GMO-soy feed going to animals and the already massive occupancy of land used for animal agriculture, trying to avoid GMO-soy while still consuming animal products is quite counter-intuitive. By consuming most factory farmed animals, you're consuming GMO-soy indirectly and in much greater quantities. Not to mention you are increasing demand for this GMO soy, which leads to more destructive land-clearing.
Again, the healthiest, more environmentally friendly, and less cruel option would be to purchase organic soy products, which are by law non-GMO. However, many people still have concerns over some of the actual proteins and chemicals inside soy.
What About Lectins?
- Lectins aren't only in soy, but present in many of foods.
- Separating lectins from their original food source isn't a viable way to study them for human consumption.
- Cooking lectins removes any negative consequences they may have.
- "High lectin" legume based diets are staples for the longest living populations and are undoubtably associated with positive health outcomes.
Another main talking-point against soy is the fact they are high in lectins. Lectins are proteins present in plants, dairy, yeast, eggs, and seafood. They can bind to other molecules, notably sugar and carbohydrate molecules, that are present both in foods, and in the membranes of our cells.
A case made by anti-grain authorities is that binding of lectins from plant foods to our cells is a major cause of ill health and nutrition malabsorption. They claim high-lectin foods like beans, grains, potatoes, tomatoes, and peanuts should be avoided for this reason.
This claim doesn't add up when you look at the actual research on lectin-containing foods.
First off, experimentation on lectins is often done in high concentrations and separated from it’s actual food source. Isolating lectins make them substantially more effective to bind to our cells compared to if they were consumed in food.
Also, by simply cooking your food, most of the lectins are deactivated or bind to other substances. Even a study from 1998, which attempts to frame lectins as a serious problem in the food industry, fails to dance around the point that lectin activity for most beans is deactivated within 10 minutes of boiling. 
Overconsumption of lectins can cause gastrointenstinal distress, but again, simply cooking your legumes/grains will remove any chance of negative consequences.
When we look at the longest living, healthiest populations in the world, known as the Blue Zone groups, “high lectin” legumes were a staple in their diet. Most of these cultures reserved meat for use as a condiment and on special occasions. In fact, the longest living Blue Zoners actually didn’t consume any meat 
Additionally, a Journal of Nutrition review concerning whole grains found that:
“Protease inhibitors, phytic acid, phenolic acids, and saponins present in whole grain have also been suggested to lower the risk of certain cancers, such as colon cancer and breast cancer. Phytic acid, lectins, phenolic acids, amylase inhibitors, and saponins have also been shown to lower plasma glucose, insulin, and/or plasma cholesterol and TG levels” 
The fact is, most people who try to write off lectin containing foods, just because they contain lectins, while absolutely ignoring all of the positive research regarding the benefits of lectin-containing foods.
This concept is most eloquently stated by Dr. David Katz, founder of the True Health Initiative :
The idea that you should renounce many of the foods most decisively and consistently linked to good health outcomes because they contain a compound that can be called a toxin may be the most egregious example of missing the forest for the trees I’ve ever seen, and I’ve spent my career scrutinizing, and repudiating, just that variety of nonsense. For the sake of false promises dangling from one gilded tree, this is a case of burning the forest down. 
What About Phytates?
- Studies on human phytate consumption is drastically different than animal studies.
- High phytate diets have been shown to be protective of bone loss in humans.
- Phytates must be consumed in the form of whole plant foods to realize the benefits and avoid the potential pitfalls.
Phytates, another compound found in soy, have been labelled as a mineral-absorption inhibitor. These phytates can wind up supposedly causing mineral loss leading to calcium deficiency and weak bones.
The original concern about phytates on bone health actualy originated from experiments done on puppies in the 1940s. These studies were followed up by research done on rats where they were fed the equivalent of 10 loaves of bread a day.
However, actual human research suggests differently. Studies where people are put on high-phytate diets actually wound up with better bone density and stronger bones (heel, spine, hip). Phytates prevented bone dissolution similar to anti-osteoporosis drugs and women with high phytate levels in the blood had a much smaller risk of major bone fractures. 
While high phytate diets may appear to be a cause for concern, the health-harming effects of this anti-nutrient
...can be manifested only when large quantities of [phytates] are consumed in combination with a [nutrient-poor] diet.
When phytates are consumed in the form of soy and whole plant foods, the result is less heart disease, diabetes, kidney stones, fractures, and possibly cancer. 
- Legume consumption is one of the pillars for long living cultures.
- Increased legume consumption (including soy) has been shown to be protective against all-cause mortality and a host of chronic diseases.
In addition to the Blue Zones study, which showed regular legume consumption as one of the pillars for the longest lived cultures , another study analyzed 785 partcipants aged 70 and over. Here were the results :
The FHILL longitudinal study shows that a higher legume intake is the most protective dietary predictor of survival amongst the elderly, regardless of their ethnicity. The significance of legumes persisted even after controlling for age at enrolment (in 5-year intervals), gender, and smoking. Legumes have been associated with long-lived food cultures such as the Japanese (soy, tofu, natto, miso), the Swedes (brown beans, peas), and the Mediterranean people (lentils, chickpeas, white beans). 
When it comes to raw statistics, the study found that every 20g of legumes consumed daily resulted in an 8% reduction in risk of death.
If you're reading this and want to eat more tofu yourself, be sure to check out our tofu press guide. Removing the water helps it absorb flavor quicker making it delicious to eat!
Soy and Estrogenic/Breast Cancer
- Soy has phytoestrogens which function differently compared to mammalian estrogens.
- Phytoestrogens can be both pro-estrogenic as well as anti-estrogenic.
- Misconceptions about hormonal impacts of soy came from research on rats who metabolize soy vastly different than humans.
- Human studies have shown soy to prevent bone loss and breast cancer.
Another major myth about soy is it’s alleged “estrogen-mimicking” chemicals, which some claim can result in breast cancer and other hormonal issues.
This is actually misinformation with no substantial evidence to support it. It's actually quite ironic because meat and dairy contain actual animal estrogens, not plant phytoestrogens.
The truth is that phytoestrogens act different than real estrogen, and can actually be pro-estrogenic in some parts of the body, but anti-estrogenic in others. Let us examine this further:
Phytoestrogens can have simultaneously pro-estrogenic and anti-estrogenic effects because there are two types of estrogen receptors: alpha and beta.
Soy phytoestrogens, such as genistein, prefer to bind to beta estrogen receptors. Beta receptor activation in the breast has an anti-estrogenic effect, which actually inhibits the growth and cancer-promoting effects of animal estrogen, can be enhance endothial function in post-menopausal women, and protect against other menopausal symptoms. 
At the same time, soy phytoestrogens can be pro-estrogenic when it comes to protecting post-menopausal women from bone loss. A robust study was done comparing soy milk consumption to progesterone cream (a common hormone therapy for post-menapausal women), and a control group.
The control group lost significant bone mineral density in their spine over the two-year study period, the progesterone group lost significantly less, and the two glasses of soy milk a day group wound up preventing bone loss and increasing bone mass. 
Pro-estrogenic and Anti-estrogenic Properties of Soy by
This misconception that soy can contribute to breast cancer came from research on rats, who metabolize soy isoflavones (phytoestrogens) quite differently from humans, as distinctly noted in the study itself. The circulating levels of geinstein in the blood in the rats that had an increase in tumor size were 58 times greater than human levels after 1 serving of soy. 
When soy consumption in humans is put to the test against breast cancer, it has been shown that soy intake during childhood, adolescence, and adult life were all associated with a decreased risk of breast cancer. Those women who ate the most soy in their youth appear to grow up to have less than half the risk. 
Breast cancer rates are much higher in the USA than in Asia, where there are some of the highest soy consumption rates. But, when Asians migrate to the US and start eating a western diet, their breast cancer rates increase to average American levels. 
Soy and Feminizing Men
- Phytoestrogens don't necessarily have pro-estrogenic properties
- Extremely high doses of soy has been shown to have some feminizing effects in a few rare cases.
- Once these extremely high doses (3 quarts of soymilk per day) were reduced, the effects were reversed.
- Nine clinical studies have shown no impact in circulating estrogen levels in men.
Everyone has heard about how too much soy consumption can result in feminizing effects in males, but is this claim substantiated?
A common reasoning for this is, again, the potential estrogenic affects of isoflavones in soy. As discussed earlier, phytoestrogens are quite different than the estrogens found in meat, and phytoestrogens can have anti-estrogenic properties in some circumstances.
Studies have found soy consumption in rat’s ability to produce offspring, but as mentioned earlier, rodent metabolism of soy is completely different, making these studies useless. 
Many have heard of how consuming too much soy can cause gynecomastia (man boobs), but the only report of this was from men consuming extremely high doses of soy, 3 quarts of soymilk a day in one instance. The feminizing effects of this extraordinary soy habit were reversed once intake was reduced. 
Finally, the peer-reviewed Fertility & Sterility journal concluded that after reviewing the clinical trials regarding soy intake and feminization there was:
“Essentially no evidence from nine identified clinical studies that isoflavone exposure affects circulating estrogen levels in men.” 
Can You Have Too Much Soy?
- Massive amounts of soy can increase IGF-1 levels.
- Vegan men eating huge amount of soy had the IGF-1 levels of meat eaters.
- Stick to 5 servings a day or less of soy to reap the benefits without the downsides.
While we’ve demonstrably proven that non-GMO soy is beneficial for our health and protective against disease, can too much soy be bad?
The answer is possibly yes. IGF-1, insulin-like growth factor 1, is a growth hormone responsible for turning children into full-grown adults. But if this hormone keeps circulating in the blood, your cells should continue to divide and grow. The more IGF-1 in the bloodstream, the higher our risk for cancer. Those on a plant based diet tend to have lower IGF-1 levels.
However, studies have shown that vegan men eating huge amounts of soy, 7 to 18 cups of soy milk worth per day, for an entire year, would up with similar levels of IGF-1 in the body as meat eaters.
How Much Soy is Too Much by
To be as safe as possible, one shouldn’t consume more than 5 servings of soy a day .
Be sure to check out our article on the best soy milk makers if you're interested in making your own soymilk.
Conclusion on Soy
Much of the controversy around soy has been the result of misrepresentation.
GMO-Soy is certainly a problem and should be labelled properly so consumers can have freedom of choice. However, the overwhelming majority GMO-soy is fed to animals, and attempting to get meat from only grass-fed sources only poses a more unsustainable problem due to limited land resources.
The best choice for consuming soy is always organic or non-GMO.
Most of the hysteria regarding the negative health risks of soy are based on the potential dangers of certain compounds (such as lectins or phytates) in isolation, but when soy itself is studied on humans, it can be protective against bone loss, breast cancer, and overall mortality.
However, to air on the safe side, stick to no more than 5 servings daily.
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