Soy was on the endo-enemy #1 list when I was first reading about the “endo diet” over a decade ago, right up there with red meat and dairy. So it’s interesting that, like red meat and dairy, soy is also in a gray area.

While researching my book, it became very clear that instead of soy being wholly damaging, its ability to damage your body (or not) is dependent on sourcing, processing, and overall quantity. That means soy can help or hinder a body in need of healing, it just depends.

So let’s dig into some of the myths and truths behind soy consumption and endometriosis and how to decide if soy is right for you!

Endometriosis Diet Myth: Soy Increases Estrogen

The original theory on why soy was bad for endo was based on a class of phytonutrients called phytoestrogens. Phytoestrogens chemically resemble estrogen, so it was assumed they could “feed” our endo growth by attaching to estrogen receptors (of which endometriosis lesions have many). Because phytoestrogens are highly concentrated in soy, it was recommended to avoid soy.

Yet, ongoing research has uncovered that phytoestrogens may actually be anti-estrogenic, leading to a lower overall concentration of estrogens available. [1]

The way this works is that sneaky phytoestrogens attach to estrogen receptors without acting like active estrogen. They “steal the seat,” so to speak. This leaves active estrogen unable to connect to estrogen receptors, which is a key feeding mechanism of endometriosis. Indeed endo is an estrogen-dependent disease because it relies on estrogen to help feed its growth (and endometriosis lesions can have up to 140 times more estrogen receptors than a normal endometrial cell). This may be why a Japanese study found that diets higher in phytoestrogens were associated with a reduced risk of advanced endometriosis. [2,3]

Just because soy has potentially helpful phytoestrogens doesn't suddenly make it a perfect endo food, though. There are still some really important considerations that balance out the “caution” side. And one considerable caution is phytates.

Endometriosis Diet Caution: Phytates in Soy

Soy beans harbor an incredibly high amount of phytates, over 10x more than rice by some accounts. [4]

Phytates are pretty cool for plant protection since they act like the gatekeeper of nutrients stored inside seeds, beans, grains, or nuts. Phytates allow these seeds to sit for months, or even years, with their nutrient stores intact so that they can have enough energy to sprout one day! They lock nutrients in, and don’t let them out until the seed is ready to germinate (i.e. it takes water to unlock the magic).

And phytates work really well to protect those nutrients! Not only will they prevent you from absorbing the nutrients in the seed (or soy in this case), but they can also bind to minerals in your body, reducing the mineral absorption from your food. This is why they’re also known as anti-nutrients since they sequester nutrients from your body!

In fact, research shows that phytates block the absorption of iron, zinc calcium, magnesium and manganese. [5]

This becomes more important to understand since soy is often marketed as a great source of iron and calcium. Unfortunately, without degrading the phytates, you may not be getting nearly as much as you thought. Phytates in soy need to be significantly degraded to .01 mg/g (that’s basically zero) in order for the iron to be better absorbed. When it’s removed, then we see iron absorption increase by as much as 12-fold. [6,7]

To put that in perspective, if your soy isn’t processed to remove phytates (see below) you may be getting 1/12 of the iron you think you are.

Lectins and Endometriosis: Immune Disruptors and Poor Quality Protein in Soy

Lectins are one class of phytates known to penetrate the gut barrier and provoke an immune response. [7] It’s why some folk with autoimmune do well on a low-lectin diet.

Lectins also make the protein in plants hard to digest and absorb thanks to their ability to inhibit the digestive enzymes amylase, pepsin, and trypsin, which facilitate the breakdown of carbohydrates and proteins. This may be why a lot of us have trouble digesting soy (or grains/beans/nuts/seeds) because their phytates are often so intact. They also turn a potentially high plant-protein food into a poor-quality protein food. [9]

Unfortunately, soy has a heavy concentration of lectins, which is one reason why an improperly prepared soy diet (phytates all left in tact) for young animals is associated with failure to thrive. [10,11]

Endometriosis Diet Caution: Herbicide Glyphosate on Soy

It’s estimated that 94% of soy in the United States is genetically modified (GM) to be resistant to the herbicide glyphosate. This allows farmers to spray this toxic product across soy fields to kill weeds without killing the soy (since the genes of the soy have been altered to tolerate it). Not only does that mean conventional (non-organic) soy is contaminated with glyphosate, it also means we’re eating genetically modified genes (if you’re wondering what eating these newfangled soy genes does to us, so am I). 

And while proponents of GM soy are enthusiastic to say it’s just like real soy, that’s simply not true. A 2013 study unequivocally rejected the notion that GM soy is equivalent to non-GM soybeans since they were found to contain high levels of residual of glyphosate (one toxic component of Round-Up), less protein, zinc, and more omega 6’s. And of the three soybeans tested (GM, conventional, and organic), the organic soybeans were by far the winner, with no glyphosate or other agrochemicals, higher levels of nutrients, and a healthier fatty acid profile. [12]

Endometriosis Soy Solutions: Organic and Fermented Soy for Endometriosis

The best way to reduce phytates is through proper preparation, which includes ways of soaking, sprouting, cooking, and fermenting. When it comes to avoiding herbicides the solution is pretty easy: buy organic.

Centuries ago, our ancestors knew the importance of fermenting soy to release its nutritional powers! This is why ancestral populations rarely, if ever, ate them non-fermented. So changed were the look and feel of soybeans upon actual consumption that early European travelers to Asia may not have associated a soybean with the soy foods being eaten - such items as soy sauce, tempeh, tofu, miso, and natto looking and tasting far differently than a soybean!

Today, the art of fermenting soybeans is nearly gone, with most of the soy we eat quickly prepared with the anti-nutrients in-tact. Not only that, but the majority is sprayed with toxic herbicides! Non-organic soy milk, soy cheeses, soy sauce (no longer fermented), soy burgers, soy protein, and quick-prepared tofu. None of these cheap soy products (on the average shelf) are fermented, all of them have herbicide residues.

With all of this in mind, we can take a step back and learn from our ancestors who enjoyed soy woven into their healthful traditions: ferment it or buy it traditionally prepared, eat it in moderation, and only purchase organic varieties.

These fundamentals, when taken together, can turn an inflammation-provoking and nutrient-robbing food into something entirely different - a food full of flavor, nutrients, and beneficial isoflavones. 

Non-fermented soy products you may consider avoiding include fresh, non-steamed soybeans (edamame) or dry soy nuts or flour, soymilk, tofu, and highly processed soy “things” (think all the soy cheeses, milk, meats, etc). Eating these foods here or there won’t “kill you,” of course, but if these make up the foundation of your diet (like me when I was a devout vegetarian) then make it a goal to kick this habit to the curb.

You can swap out soy cheese for homemade pre-soaked (to remove phytates) cashew cheese. Soy milk? Replace with your own (pre-soaked for 12 hours) nut, seed, or oat milk. Soy burgers? Make your own veggie burgers without the soy and without all the terrible vegetable oils (eww).

Traditionally fermented products that are easier to find include tempeh, miso, soy sauces, natto and fermented tofu or soy milk products. The manufacturer should market the product as fermented since this is a process that takes time and they will be proud.

It’s best to know your producer and their methods or, even better, play around with making your own at home! Check out these cool blog posts here and here if you’re interested in some fun kitchen tofu experimentation!

Want to learn more about your most pressing endometriosis diet and lifestyle questions? Make sure to check out my book, Heal Endo: An Anti-Inflammatory Approach to Healing From Endometriosis, available now

1. Pugeat, M., Nader, N., Hogeveen, K., Raverot, G., Déchaud, H., & Grenot, C. (2010). Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome. Molecular and cellular endocrinology, 316(1), 53–59. https://doi.org/10.1016/j.mce.2009.09.020

2. Chen, H., Malentacchi, F., Fambrini, M., Harrath, A. H., Huang, H., & Petraglia, F. (2020). Epigenetics of estrogen and progesterone receptors in endometriosis. Reproductive Sciences (Thousand Oaks, Calif.), 27(11), 1967–1974. https://doi.org/10.1007/s43032-020-00226-2

3. Tsuchiya, M., Miura, T., Hanaoka, T., Iwasaki, M., Sasaki, H., Tanaka, T., Nakao, H., Katoh, T., Ikenoue, T., Kabuto, M., & Tsugane, S. (2007). Effect of soy isoflavones on endometriosis: interaction with estrogen receptor 2 gene polymorphism. Epidemiology (Cambridge, Mass.), 18(3), 402–408. https://doi.org/10.1097/01.ede.0000257571.01358.f9

4. Chen, K. I., Chiang, C. Y., Ko, C. Y., Huang, H. Y., & Cheng, K. C. (2018). Reduction of Phytic Acid in Soymilk by Immobilized Phytase System. Journal of food science, 83(12), 2963–2969. https://doi.org/10.1111/1750-3841.14394

5. Gupta RK, Gangoliya SS, Singh NK. Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains. J Food Sci Technol. 2015 Feb;52(2):676-84. doi: 10.1007/s13197-013-0978-y. Epub 2013 Apr 24. PMID: 25694676; PMCID: PMC4325021.

6. Hurrell, R. F., Juillerat, M. A., Reddy, M. B., Lynch, S. R., Dassenko, S. A., & Cook, J. D. (1992). Soy protein, phytate, and iron absorption in humans. The American journal of clinical nutrition, 56(3), 573–578. https://doi.org/10.1093/ajcn/56.3.573

7. Hurrell R. F. (2004). Phytic acid degradation as a means of improving iron absorption. International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition, 74(6), 445–452. https://doi.org/10.1024/0300-9831.74.6.445

8. Vojdani A, Afar D, Vojdani E. Reaction of Lectin-Specific Antibody with Human Tissue: Possible Contributions to Autoimmunity. J Immunol Res. 2020 Feb 11;2020:1438957. doi: 10.1155/2020/1438957. PMID: 32104714; PMCID: PMC7036108.

9. Liener I. E. (1994). Implications of antinutritional components in soybean foods. Critical reviews in food science and nutrition, 34(1), 31–67. https://doi.org/10.1080/10408399409527649

10. Wen, Y., Liu, A., Meng, C., Li, Z., & He, P. (2021). Quantification of lectin in soybeans and soy products by liquid chromatography-tandem mass spectrometry. Journal of chromatography. B, Analytical technologies in the biomedical and life sciences, 1185, 122987. https://doi.org/10.1016/j.jchromb.2021.122987

11. Fasina, Y. O., Classen, H. L., Garlich, J. D., Swaisgood, H. E., & Clare, D. A. (2003). Investigating the possibility of monitoring lectin levels in commercial soybean meals intended for poultry feeding using steam-heated soybean meal as a model. Poultry science, 82(4), 648–656. https://doi.org/10.1093/ps/82.4.648

12. Bøhn, T., Cuhra, M., Traavik, T., Sanden, M., Fagan, J., & Primicerio, R. (2014). Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans. Food chemistry, 153, 207–215. https://doi.org/10.1016/j.foodchem.2013.12.054