Soy and Breast Cancer: From Misconception to Protective Superfood
For years, soy was mistakenly believed to increase breast cancer risk due to its phytoestrogen content. However, extensive research—and expert recommendations from physicians like Dr. Kristi Funk—has debunked this myth, revealing that soy consumption is not only safe but may actually offer protective benefits against breast cancer.
Understanding the Soy Estrogen Myth
Soy contains isoflavones, plant-based compounds that can weakly mimic estrogen in the body. Early animal studies suggested a potential link between high isoflavone intake and increased breast cancer risk, but these studies used doses much higher than typical human consumption and involved rodents that metabolize isoflavones differently than humans. More recent human studies and clinical reviews show that soy does not increase breast cancer risk—and in fact, it may lower it.
Research shows that phytoestrogens in soy preferentially bind to estrogen receptor beta (ERβ), which is associated with protective and anti-proliferative effects. By contrast, the body’s own estrogen tends to bind more strongly to estrogen receptor alpha (ERα), which can stimulate cell growth and, in some cases, promote cancer development. This receptor difference is one reason soy is now understood to be protective rather than harmful for breast health.
The American Cancer Society confirms that soy foods are safe for women with breast cancer and may even be protective, particularly when consumed in childhood or adolescence and continued into adulthood.
What Dr. Kristi Funk Recommends
Dr. Kristi Funk, a board-certified breast cancer surgeon and author of Breasts: The Owner’s Manual, is a strong advocate for incorporating soy into the diets of women, including breast cancer patients and survivors.
Her recommendations:
Consume 2–3 servings of soy daily.
Even ½ serving per week has been associated with a reduction in recurrence and mortality.
Stick to whole or minimally processed soy foods—like tofu, tempeh, soy milk, miso, and edamame.
Avoid heavily processed soy isolates and supplements.
Types of Soy Foods
There are many delicious and nutritious soy products to enjoy:
Tofu – Mild in flavor, versatile in savory or sweet dishes. Comes in Silken, Firm, Extra Firm. Check your recipe for the best tofu for your case.
Tempeh – Fermented and nutty, with a firm texture.
Edamame – Young green soybeans, steamed or boiled.
Soy Milk – A dairy-free milk alternative.
Miso – Fermented soybean paste, often used in soups and sauces.
Soy Sauce – Fermented, salty condiment.
Soy Nuts – Roasted soybeans eaten as a snack.
Best Ways to Eat Soy
To get the most benefit from soy:
Choose whole or fermented forms (tofu, tempeh, miso, edamame).
Use firm or extra firm tofu in stir-fries, or in sandwiches, or top salads. Tofu has little flavor on its own, but will absorb whatever flavors are in your dish. Marinate it!
Bonus tip. It’s helpful to drain your tofu, to remove excess water. This way, it will fully absorb flavors. You don’t need a dedicated tofu press to get the job done. Wrap your tofu in paper towels or a cotton dish cloth and sandwich it between cutting boards, weighted with a heavy pot or books. Keep an eye that your weight stack doesn’t tip over! 10-15 minutes of pressing should do the trick.
Make a tofu scramble for brunch
Add edamame to salads, or eat as a snack!
Soy milk can be used in overnight oats, smoothies, etc. A great substitute for dairy milk.
Tempeh can be made into “bacon” or incorporated into a sweet potato hash.
Tofu Bacon
1 package (8 oz) tempeh, sliced into thin strips
1 1/2 T tamari or soy sauce
1 1/2 T maple syrup
1T apple cider vinegar
1/8 t cumin
1/4 t smoked paprika
Mix all ingredients, minus tempeh, in shallow bowl or container. This will be your marinating vessle so think shallow and flat. Submerge the tempeh strips in marinade and keep in the refrigerator for at least 30 minutes and up to a few hours.
Bake at 350 for 15-20 minutes (depending on your desired crispness). Enjoy!
Soy in Japanese Culture and Breast Cancer Rates
In Japan, where soy consumption is a daily norm—often through miso soup, tofu, and natto—breast cancer rates have historically been significantly lower than in Western countries. While other lifestyle and genetic factors play a role, epidemiological studies suggest that the regular, lifelong intake of soy foods contributes to this protective trend3.
Final Thoughts
The latest evidence from reputable sources and experts like Dr. Kristi Funk shows that soy is not only safe but highly beneficial for women’s health, especially in relation to breast cancer. Incorporating whole, minimally processed soy foods into your diet can be a powerful, science-backed strategy for prevention and survivorship.
Yum Sauce
Stay tuned for more ways to incorporate soy into your diet! No more bland tofu.
Nature offers incredible tools for health and vitality. If you want support integrating these into your lifestyle, I’d love to work with you! Check out my coaching and workshops on the Work With Me page.
References
American Cancer Society. (2023). Soy and Cancer Risk: Our Expert's Advice ↩
Funk, K. (n.d.). Should You Be Eating Soy? Setting the Record Straight ↩
Messina M, Wu AH. The importance of soy protein and soy isoflavones in the prevention and treatment of breast cancer. J Steroid Biochem Mol Biol. 2009; 118(4-5): 201–210. doi:10.1016/j.jsbmb.2009.10.005
Yamamoto, S., et al. (2003). Soy, isoflavones, and breast cancer risk in Japan. J Natl Cancer Inst, 95(12), 906-913. PubMed ↩