I’ve been wondering for years why everyone seems to hate soy. As a part-time job during naturopathic medical school I used to sample health foods at various grocery stores and customers were so avid that they avoid soy. When I asked them why, they said, “Soy causes cancer”. This is a common misconception about soy. In fact, there’s evidence that soy consumption decreases the risk of many cancers such as endometrial, ovarian, gastrointestinal, breast, and prostate. If that’s not enough, I personally grew up on soy and I’ve turned out okay…so far! In a world full of fast food, microwavable meals, and plastic everything – is an innocent bean really the enemy? Since I’m passionate about female hormones, I hit the books and researched the effects of soy on estrogen and progesterone levels. I hope you’ll be pleased to read what I’ve discovered, and accept that soy isn’t so scary after all!
The components of soy: what’s in a bean?
- Protein– soy contains the complete spectrum of essential amino acids, which is why it is a staple in a vegetarian diet.
- Isoflavones– these are the constituents that act like estrogen and are the reason why it’s common to get confused about soy. Another term for isoflavone is phytoestrogen. Isoflavones/phytoestrogens can exert weak estrogenic effects in our bodies. This means they can bind to estrogen receptors in the body and prevent strong/harmful estrogens from binding. This is a good thing! It does not promote cancer, it protects us.
- Beta-sitosterols– these are constituents that have been proven to lower cholesterol. Soy is recommended by Health Canada as part of a cholesterol lowering diet.
- Vitamins & Minerals– soy is high in fiber, iron, folate, and B-vitamins. If you’re concerned about the bioavailability of nutrients in beans, opt for sprouted beans.
- “Fermentability”– I may have made up this word, but I’m using it to explain all of the wonderful foods that have been created by fermenting soy, like: tempeh, miso, and natto! Fermented foods are amazing for gut health, lowering inflammation, and benefiting mood.
The Top 5 Benefits of Soy for Women
- Soy isoflavones bind to estrogen receptors and promote the urinary excretion of estrogen in estrogen dependent conditions like endometriosis and fibroids. With increased amounts of soy consumption, severity of endometriosis can decline and women can experience fewer symptoms.
- In menopausal women with low estrogen levels, soy consumption can improve serum estradiol levels and reduce hot flashes and symptoms of declining estrogen.
- In women undergoing IVF, those with higher soy consumption had increased fertilization rates. Women who consumed soy, compared to women who did not, had a 6% greater chance of fertilization.
- Not only can soy improve fertilization, but also pregnancy and live birth rates. In women who consume soy, there’s an 11-13% greater chance of pregnancy and birth rate compared to women who don’t eat soy.
- Soy increases a protein called sex-hormone-binding-globulin (SHBG). This protein binds estrogen and testosterone in the blood. If these hormones are bound then they are inactive, a greater ratio of bound hormone to free hormone can lower symptoms of androgen excess, like: acne, hair loss, and male pattern hair growth, as well as estrogen excess, like: breast tenderness, painful periods, and heavy periods.
What about men consuming soy? Here’s where it gets less obvious
There is a lot of conflicting research on the effects of soy consumption in men. For example, one human study showed that soy consumption lowers sperm concentration, and another showed that soy has no effect on any semen parameters. Soy has the potential to decrease testosterone levels in men who already have hypogonadism (low testosterone). It may exert estrogenic effects in men but the research is varied. However, it is undisputed that soy has great cardiovascular benefits and can lower cholesterol levels. It may also present a preventive role against prostate cancer and benign prostatic hypertrophy (BPH). If you’re male and you’re not trying to conceive, the benefits of soy likely outweigh the potential risks. It is ideal for man to eat a variety of plant and animal sources of protein; soy can be included in this daily diet.
The Bottom Line:
- Opt for non-GMO, organic, and sugar free soy products
- WOMEN: aim for 7-28mg of isoflavones daily (one cup of soy milk has about 6mg, 3 ounces of tofu has 20mg
- MEN: when not trying to conceive, aim to consume about 3 servings of soy a week
Book an appointment with Dr. Sumner HERE
Die, M. D., Bone, K. M., Williams, S. G., & Pirotta, M. V. (2014). Soy and soy isoflavones in prostate cancer: a systematic review and meta‐analysis of randomized controlled trials. BJU international, 113(5b), E119-E130.
Chavarro, J. E., Toth, T. L., Sadio, S. M., & Hauser, R. (2008). Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Human reproduction, 23(11), 2584-2590.
Vanegas, J. C., Afeiche, M. C., Gaskins, A. J., Mínguez-Alarcón, L., Williams, P. L., Wright, D. L., … & Chavarro, J. E. (2015). Soy food intake and treatment outcomes of women undergoing assisted reproductive technology. Fertility and sterility, 103(3), 749-755.
Tsuchiya, M., Miura, T., Hanaoka, T., Iwasaki, M., Sasaki, H., Tanaka, T., … & Tsugane, S. (2007). Effect of soy isoflavones on endometriosis: interaction with estrogen receptor 2 gene polymorphism. Epidemiology, 18(3), 402-408.
Saeidnia, S., Manayi, A., Gohari, A. R., & Abdollahi, M. (2014). The Story of Beta-sitosterol-A Review.
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.
Chen, M., Rao, Y., Zheng, Y., Wei, S., Li, Y., Guo, T., & Yin, P. (2014). Association between soy isoflavone intake and breast cancer risk for pre-and post-menopausal women: a meta-analysis of epidemiological studies. PloS one, 9(2), e89288.