Over the past couple decades, soy products have become quite controversial with claims that they are estrogenic, cause breast cancer, are heavily processed and genetically modified. Because of this, I would like to clear up the confusion.

Myth #1 – Soy is Feminizing

Many people claim that soy is estrogenic and feminizing because it contains phytoestrogens known as isoflavones. These claims primarily stem from some rodent studies and a couple rare human cases where individuals consumed in the ballpark of 15 to 20 servings of soy per day and reported gynecomastia (breast growth in men).^[1] That’s hardly sufficient evidence to support the idea that soy, in reasonable amounts, is feminizing.

Fortunately, researchers have performed multiple meta-analyses where they looked at all the research on the topic of soy and isoflavones and found no link between soy consumption and feminization, low testosterone, or high estrogen levels in men.^[2][3] Similarly, a 2009 meta-analysis found that soy had no effect on estrogen levels in women.^[4]

This is because the phytoestrogens in soy are 1,000 times weaker and preferentially bind to different receptors in our bodies than true human estrogens do.^[5][6] This allows soy to actually have anti-estrogenic effects in tissues where we don’t want excess estrogen (e.g., breast tissue), which may also be why soy products have been shown to improve menopausal symptoms.^[7]

Unlike soy, however, dairy contains mammalian estrogens (even if no hormones are added), which has the same effect as the estrogen produced by our own bodies, and is therefore pro-estrogenic.^[8] So if you’re worried about the hormonal effects of your food choices, it may be worth ditching dairy for a healthy plant-milk such as soy.

Myth #2 – Soy Causes Breast Cancer

Another common concern is the issue of breast cancer. What you may find surprising is that soy consumption in Asia is actually linked to a lower risk of breast cancer. In fact, those who consume just ½ a cup of tofu per day reduce their risk of developing breast cancer by an astonishing 30% compared to those who avoid soy!^[9] Even women who previously battled breast cancer have 21% greater survival rates over the course of 9 years if they consume more soy.^[10] And finally, those with BRCA gene mutations, which put them at higher risk of breast cancer, also may benefit from increased soy consumption.^[11] This is likely due to the anti-estrogenic effects of soy in breast tissue that I discussed earlier.^[5][6]

But what about other cancers? A study including over 46,000 women found a 30% reduction in endometrial cancer risk in the group with the highest soy consumption.^[12] Furthermore, studies on soy intake and prostate cancer risk in men have found anywhere from a 20% to a whopping 70% reduction in those with higher soy intakes.^[13] I should note that dairy, on the other hand, may actually increase prostate cancer risk.^[14]

While soy clearly doesn’t have a negative impact on hormones or cancer, there may be other reasons to consume soy products as well. Just ½ cup of whole soybeans contains 16 grams of protein, 5 grams of fiber, over half your daily requirement for iron, and significant amounts of magnesium, copper, and manganese. This makes soy the highest protein legume, with 37% of its calories coming from protein! In addition, it contains significant amounts of many B vitamins and vitamin K. Even though tofu is somewhat processed and removes some of the fiber and minerals, soy is so packed with nutrition that it is still quite a healthy food.

Soy protein intake has also been shown to reduce cholesterol levels, which helps reduce cardiovascular disease risk. On top of that, soy reduces inflammation, which is a contributor to just about every chronic illness we know of.^[15]

The American Academy of Pediatrics also suggests that a soy-based formula is the nutritional equivalent of cow’s milk formula and is suitable for full-term infants with no evidence of hormonal effects.^[16]

Myth #3 – Soy Products Contain GMOs & Pesticides

Lastly, there is a fair amount of concern around genetically modified (GMO) soy products and the pesticides used to produce them; however, nearly every major food producer uses non-GMO soy for human consumption. The GMO crops are primarily fed to livestock (chickens, pigs, cattle) who will then be fed to humans. But if you’re still concerned, check the labels on your soy products to ensure they are made with non-GMO and/or organic soybeans.

So there it is! Unless you have a specific allergy or sensitivity to soy, there is no reason to avoid a food that not only doesn’t harm your health, but has countless benefits ranging from its jam packed nutrient profile to a reduction in cancer risk.

References

1. Martinez, J & Lewi, JE. An unusual case of gynecomastia associated with soy product consumption. Endocrine Pract. 2008;14(4):415-418
2. Messina, M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril. 2010;93(7):2095-2104
3. Hamilton-Reeves, JM et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94(3):997-1007.
4. Hooper, L et al. Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis. Human Reproduction Update. 2009;15(4):423-440
5. McCarty, MF. Isoflavones made simple – Genistein’s agonist activity for the beta-type estrogen receptor mediates their health benefits. Medical Hypothesis. 2006;66:1093-1114.
6. Mostrom, M. & Evans, TJ. Phytoestrogens. Reproductive and Developmental Toxicology. 2011.
7. Toku, K et al. Extracted or synthesized soy isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause. 2012;19(7):776-790.
8. Maruyama, K et al. Exposure to exogenous estrogen through intake of commercial milk produced from pregnancy cows. Pediatrics International. 2012;52:33-38.
9. Wu, AH et al. Epidemiology of soy exposure and breast cancer risk. Br J Cancer. 2008;98(1):9-14.
10. Zhang, FF et al. Dietary isoflavone intake and all-cause mortality in breast cancer survivors: The Breast Cancer Family Registry. Cancer. 2017:2070-2079.
11. Kwang-Pil, K et al. Dietary intake and breast cancer among carriers and noncarriers of BRCA mutations in the Korean Hereditary Breast Cancer Study. Am J Clin Nutr. 2013;98:1493-1501.
12. Ollberding, NJ et al. Legume, soy, tofu, and isoflavone intake and endometrial cancer risk in postmenopausal women in the multiethnic cohort study. J Natl Cancer Inst. 2012;104(1):67-76.
13. Hwang, YW et al. Soy food consumption and risk of prostate cancer: a meta-analysis of observational studies. Nutr Cancer. 2009;61(5):598-606.
14. Aune, D et al. Dairy products, calcium, and prostate cancer risk: a systematic review and meta-analysis of cohort studies. Am J Clin Nutr. 2015;101(1):87-117.
15. Ramdath, DD et al. Beyond the Cholesterol-Lowering Effect of Soy Protein: A Review of the Effects of Dietary Soy and Its Constituents on Risk Factors for Cardiovascular Disease. Nutrients. 2017;9(4):e324
16. Bhatia, J et al. Use of Soy Protein-Based Formulas In Infant Feeding. Pediatrics. 2008;121(5):1062-1068.