For quite some time, there has been confusion and controversy about the consumption of soy products, especially in plant-based diets where they may be  eaten more routinely and abundantly. This controversy has centered on  two well known isoflavones, genistein and daidzein, that are  plant estrogens (phytoestrogens) found in soybeans. Since elevations in the production, drug intake, and circulation of natural human estrogens have been linked with an increased risk of cancer in the breast, ovaries, and endometrium in women, there has been  concern that an increase of phytoestrogens may similarly contribute to cancer risk. However, a vast body of evidence strongly indicates that this concern is unwarranted and that soy products have significant health benefits. (1) 

In the human body there are two different receptors for estrogen, alpha and beta, to which estrogen can attach and exert a variety of effects. Estrogens produced in the ovaries and fat cells, or taken as hormone replacement drug therapy, preferentially bind with the estrogen alpha receptor, and can send signals to hormone-positive cancer cells to grow. Phytoestrogens in soy products, however, bind with a significantly greater affinity to the estrogen beta receptor, which exerts an anti-estrogen, anti-cancer effect. Yet, soy phytoestrogens can also bind with low affinity to the alpha receptors, thereby blocking high levels of cancer promoting body estrogen from attaching to them, while also producing only 1-10%  the cancer-signaling capacity of body estrogen. thereby significantly reducing cancer risk. (1) 

Soy products also decrease the level of circulating estrogens by blocking the conversion of other steroids into estrogen, (2)and genistein has been shown to block the binding of the body estrogen estradiol to breast cancer cells, thereby inhibiting cancer cell growth. (3)Furthermore, soy phytoestrogens not only reduce cancer risk by blocking cancer-promoting receptors in the breast; they also stop the excessive production of body estrogen by blocking the estrogen-promoting enzyme aromatase in breast cancer cells. (4)Cancers of the uterus and ovaries are also mediated only by the alpha receptors, so soy products don’t have no cancer promoting effects on these other reproductive organ cancers. In fact, phytoestrogens are linked to protective effects, and studies have shown that women who ate the most soy products had 30% less endometrial cancer and almost 50% less ovarian cancer. (5) 

In some of the largest soy studies to date, extending over many years, even small amounts of soy products (one-half to one serving a week) were associated with significant decreases in mortality from and recurrence of breast cancer. (6)(7)And an extensive review of five cohort studies including over 11,000 subjects concluded that soy definitively does not increase breast cancer but in fact decreases the occurrence, recurrence, and death rate—in every single study. (8)The benefit and effectiveness of soy products is further vindicated by epidemiological studies and observations of Chinese and Japanese women in Asia, who consume diets rich in soy foods yet have remarkably low breast cancer rates. (9)(10)(11) 

There has also been some controversy and confusion about the potential negative goitrogenic impact of soy products on the production of thyroid hormones and thyroid function. Thyroid hormones are essential to fat, sugar, and energy metabolism, and when these hormones are reduced, there can be reactive weight gain even with lowered calorie intake. In addition, when thyroid hormones are low, the brain attempts to stimulate thyroid function by increasing the release of thyroid-stimulating hormone (TSH) that can promote an enlargement of the thyroid known as a goiter. There is some evidence that soy in the diet can modestly raise the levels of thyroid stimulating hormone (a marker for lower thyroid function), but there was no evidence of any negative effects on the production of thyroid hormones or thyroid function. (12) 

In an extensive review of both healthy adults and patients with low thyroid function, there was no significant evidence that soy foods had any negative effect on people with normal thyroid function and adequate iodine intake. However, in patients with already existing low thyroid function, and in whom iodine intake is deficient, there is some evidence that soy foods may promote some decrease in thyroid function, requiring an increase of the dose of thyroid hormone. (13)Consistent with these data, iodine deficiency greatly increased anti-thyroid effects of soy products, and iodine supplementation is protective of any negative impact of soy on thyroid function. (14)The consensus of the evidence base is that people with low thyroid function can consume modest amounts of soy food products and experience the benefits in their diet as long as they maintain adequate iodine in their diets. The daily need for iodine is 150 micrograms daily for adults, which can be obtained by including the seaweeds dulse and nori in your diet or by taking iodine in supplemental form. 

Edamame (immature soybeans) and soy milk made from just organic soybeans and water ( oil and sugar free) are considered whole soy foods that can be eaten several times a week. Enjoy soy milk on your morning cereal and in recipes calling for plant milk, and choose edamame as a main/side dish or snack. Other common soy foods are processed from edamame (soybeans)  . Tofu is made of soybeans that are boiled and crushed, treated to separate the curds and whey, and pressed into blocks; tempeh, miso, and natto are fermented. Fermentation of soy products has been shown to provide additional health benefits to your diet because it significantly reduces phytates and converts the  isoflavones in soy into their most active form. (1) 

The natural process of fermentation also provides a diversity of probiotic organisms to your gut microbiota that can decrease gut inflammation and support healthy function of your digestive and immune systems. In addition to the benefits already mentioned, soy products provide a complete protein source containing all the essential amino acids, and may help lower risky LDL-cholesterol and provide some protection against osteoporosis. 

In light of the benefits of soy products, foods made from processed soybeans can be included in the whole food plant-exclusive, SOS-free, eating plan. However, for health and weight regulation, it is good to eliminate as much processed food as possible. So if you decide to diversify your diet, and incorporate these products in your dietary plan, I recommend tofu, tempeh, miso, and natto be eaten in moderation,  about six to eight ounces of organic, non-GMO soy products per week. Try dishes such as scrambled organic tofu for breakfast or tofu/tempeh stir-fry with vegetables (with-out oil) for lunch or dinner. 

Other soy-based items (some soy milks, soy cheeses, soy-based meat substitutes, etc.) are made with ultra-processed soy protein derivatives and soy protein isolates; these are to be avoided entirely. Also, always keep in mind that soybeans are one of the most disturbingly genetically- modified (GMO) crops on the planet, heavily sprayed with the toxic herbicide glyphosate, so it’s critical to make sure that any soy products you buy are 100% organic and GMO-free. 

It’s interesting to me how the subversive forces of our food industry and government have shackled people with fear and continue to tell them to avoid soy products at all costs, while excesses of milk, dairy, animal products, processed foods, and refined sugar, which are much more notorious for heart disease and cancer risk, fly under the radar. I hope that this bothers you as much as it bothers me. Let’s be realistic. The epidemics of heart disease, cancer, and obesity in the U.S. are not due to the overconsumption of soybeans! The use of certain soy products can help you diversify your diet, and ensure your commitment to a whole food plant-exclusive, SOS-free dietary plan. 

References

•         Funk K. Breasts: The Owner’s Manual. Nashville, TN: Thomas Nelson; 2018.
  
•         Kellis JT et al. Inhibition of human estrogen synthetase (aromatase) by flavones. Science. 1984;225(4666):1032-1034. 
•         Fioravanti L, Cappelletti V, et al. Genistein in the control of breast cancer cell growth: insights into the mechanism of action in vitro. Cancer Lett. 1998;130(1-2):143-152. 
•         Rice S, Mason HD, Whitehead SA. Phytoestrogens and their low dose combinations inhibit mRNA expression and activity of aromatase in human granulosa-luteal cells. J Steroid Biochem Mol Biol. 2006;101(4-5):216-225.
  
•         Greger M. Who shouldn’t eat soy? https://nutritionfacts.org/ video/who-shouldnt-eat-soy/ Published November 25, 2016.
  
•           Zhang FF, Haslam DE, et al. Dietary iso avone intake and all-cause mortality in breast cancer survivors: The Breast Cancer Family Registry. Cancer. 2017;123(11):2070-2079. 

•         Shu XO, Zheng Y, et al. Soy food intake and breast cancer survival. JAMA. 2009;302(22):2437-2443. 
•         Chi F, Wu R, et al. Post-diagnosis soy food intake and breast cancer survival: a meta-analysis of cohort studies. Asian Pac J Cancer Prev. 2013;14(4):2407-2412. 
•         Greger M. How to block breast cancer’s estrogen produc- ing enzymes. https://nutritionfacts.org/video/how-to-block- breast-cancers-estrogen-producing-enzymes/ Published April 17, 2007.
  
• Pisani P, Bray F, Parkin DM. Estimates of the world-wide prevalence of cancer for 25 sites in the adult population. Int J Cancer. 2002;97(1):72-81. 
• Lee HP, Gourley L, et al. Dietary effects on breast-cancer risk in Singapore. Lancet. 1991;337(8751):1197- 1200. 
• Otun J, Sahebkar A, et al. Systematic Review and Meta-analysis on the effect of soy on thyroid Function. Sci Rep. 2019;9(1):3964. Published 2019 Mar 8.
  
• Messina M, Redmond G. Effects of soy protein and soybean iso avones on thyroid function in healthy adults and hypo-thyroid patients: a review of the relevant literature. Thyroid. 2006;16(3):249-258. 
• Doerge DR, Sheehan DM. Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect. 2002;110 Suppl 3(Suppl 3):349-353.