Updated: Sep 9, 2021
Many people believe that soy foods increase the risk of breast cancer.
I believe this idea that soy increases breast cancer risk is that soy contains isoflavone that is plant estrogens. High levels of estrogen have been linked to an increased risk of breast cancer and hormonal cancers.
On the contrary, organic soy contains beneficial phytoestrogens that block cell receptors from other harmful estrogens in animal products and chemical estrogenic compounds such as Xeno/Metallo-estrogens from entering the cells and causing damage (1).
Soy isoflavones decrease the invasiveness of breast cancer cells and regulate genes and cellular signalling involved with tumour initiation, promotion, and progression (2). Soy also seems to reduce IGF-1 levels and thus inhibits cancer growth (3). High levels of IGF-1 can induce cancer cell proliferation and inhibit apoptosis.
Moreover, soybeans contain genistein with high antioxidant properties. It influences enzymes that regulate cell growth and division and induces apoptosis or programmed cell death (4). It also has an anti-angiogenic effect i.e., it inhibits the formation of blood vessels that feed cancer cells in breast, prostate, and ovarian cancer cells (5). A genistein supplemented diet in studies on mice with breast tumours was found to reduce lung metastases 10-fold (6).
A Chinese study conducted in 2009 examined the safety of soy food consumption among 5000 women with breast cancer diagnoses (7). After 4 years, it was found that women with the highest intake of soy had a 29% lower risk of death and 32% less likely to have breast cancer recurrence.
Soy intake also improves the effectiveness of tamoxifen use (8) in lowering the risk of breast cancer recurrence by 35%.
However, if you are allergic to soy, be it from an autoimmune condition, thyroid imbalances or G6PD deficiency, you should avoid or limit your soy intake (10).
On the other hand, phytoestrogens found in soy protect us from hormonal cancers by binding the estrogen receptor and displacing the strong and potentially harmful estrogens such as estradiol and estrone. They prevent the accumulation of environmental estrogens in breast tissue.
The Fabulous Five Phytoestrogens (9)
Get Your Five Fab Phytoestrogens Daily (Suggested Amounts)
Flaxseed freshly ground (2-4 TB per day)
Organic soy and tofu (½ cup tofu or 1 ½ cup soy milk)
Raw pumpkin seeds (1-2 TB daily)
Clover sprouts (3 cups weekly)
Mung bean sprouts (3 cups weekly)
Watch out for our Recipe e-book with great ideas to prepare tasty healthy vegan food.
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(1) Sat Dharam Kaur N.D. “Healthy Breast Foundation Program”2016
(2) T. Am Coll “Nutrition” april 24(2): 1465-1495
(3) Takata Y., Masjkarinec G, Rinaldi S, Kaaks R, Nagata C “Serum Insulin-like growth factor-1 levels among women in Hawaii and Japan with different levels of tofu intake” nutrition Cancer. 2006; 136-42
(4) Douglas CC, Johnson SA, Arjmandi BH, “Soy and its Isoflavones: the truth behind the science in breast cancer. Anticancer Agents med Chemicals. 2013 Oct; 13(8):1178-87
(5) Biochem Pharmacol 2005 Jan 15;69(2):307-18
(6) Cancer Research 2005 apr 15;65(8):3396-403
(8) Shu Xo, Zheng Y, Cai H et al “Soy food intake and breast cancer survival. JAMA 2009 Dec 9;302(22):2437-43
(9) Sat Dharam Kaur N.D. “Healthy Breast Foundation Program”2016