Debunking anti-soy confusion

Debunking the Anti-Soy Confusion

Over the past 20 years, soy has been both popularized and un-popularized as a health food. Despite the preponderance of scientific evidence in support of whole soy foods, the public has now been convinced that soy products may contribute to excessive estrogen production in both males and females, leading to adverse health effects in both sexes.

Soy products get a bad reputation for the following reasons:

  • Some say that soy products act as endocrine disruptors
  • Some believe that eating soy can cause “feminization” in men
  • Some internet sources claim that soy can increase breast cancer risk in women
  • Some believe that soy can reduce testosterone levels in men
  • Some believe that soy products can reduce thyroid hormone production
Research shows that this anti-soy perspective is not grounded in scientific data, and is rather a misinterpretation of the truth.


Soy and Breast Cancer

Minimally processed soy products like edamame, tofu and tempeh contain isoflavones, an estrogen mimic that actually reduce the rate of breast cancer.

In the Soy Food Intake and Breast Cancer Survival study, 5,042 breast cancer survivors were studied to understand the connection between soy intake and breast cancer recurrence. In women living with breast cancer, increased soy intake was significantly associated with decreased risk of death and recurrence (1).

In 2011 the Soy Food Consumption and Breast Cancer Prognosis study clearly demonstrated that as isoflavone intake increased, the risk of death from breast cancer decreased (2).

Soy and Prostate Cancer

Studies investigating the connection between soy products and prostate cancer reveal that soy actually reduces the risk of prostate cancer by about 25% (3). In addition, increased soy consumption has actually been associated with a reduced risk for lung cancer, stomach cancer and colorectal cancer (4–6).

Scientists believe that the isoflavones in soy have a number of anti-cancer effects that have nothing to do with their ability to bind to the estrogen receptor. In other words, isoflavones in soy may have numerous other beneficial actions beyond their role in estrogen metabolism.

How Much Soy is Safe to Eat?

When soy products first hit the market, food manufacturers made everything out of soy, and marketed these products as alternatives to animal protein. These marketing techniques still exist today, although the anti-soy media has reduced the abundance of soy products in the grocery store dramatically.

When humans consume animal protein, the production of a hormone known as insulin-like growth factor 1 (IGF-1) increases significantly. IGF-1 is a potent growth signal that promotes cancer development and tumor formation in many animal and human studies.

That being said, eating as much as 7 to 18 servings of soy per day may be too much, and negate the beneficial effects of avoiding animal protein. In some studies, between 5 and 10 servings of soy protein per day increased IGF-1 production, but in others as few as 2 to 3 servings of soy protein per day does not increase IGF-1 production (7,8).

Take Home Messages

  • It’s hard to argue with the data: eating soy will NOT increase your cancer risk.
  • An overwhelming collection of data shows that minimally processed soy products can significantly reduce your risk for the development of many types of cancers, including breast cancer, prostate cancer, lung cancer, stomach cancer and colorectal cancer.
  • Most importantly, if you choose to incorporate soy into your diet, do so using a sensible approach, and eat a wide variety of legumes as well, including beans, lentils and peas. In the plant world, diversity your diet as much as possible and eat the rainbow every day in order to maximize your micronutrient diversity

Leave a Comment Below

Leave a comment below and let us know what you think of soy products. Have you been told they are good or bad, and what do you believe?


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  1. Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, et al. Soy Food Intake and Breast Cancer Survival. JAMA J Am Med Assoc. 2009 Dec 9;302(22):2437–43.
  2. Caan BJ, Natarajan L, Parker B, Gold EB, Thomson C, Newman V, et al. Soy food consumption and breast cancer prognosis. Cancer Epidemiol Biomark Prev Publ Am Assoc Cancer Res Cosponsored Am Soc Prev Oncol. 2011 May;20(5):854–8.
  3. Hwang YW, Kim SY, Jee SH, Kim YN, Nam CM. Soy Food Consumption and Risk of Prostate Cancer: A Meta-Analysis of Observational Studies. Nutr Cancer. 2009 Sep 23;61(5):598–606.
  4. Yang W-S, Va P, Wong M-Y, Zhang H-L, Xiang Y-B. Soy intake is associated with lower lung cancer risk: results from a meta-analysis of epidemiologic studies. Am J Clin Nutr. 2011 Dec 1;ajcn.020966.
  5. Kim J, Kang M, Lee J-S, Inoue M, Sasazuki S, Tsugane S. Fermented and non-fermented soy food consumption and gastric cancer in Japanese and Korean populations: A meta-analysis of observational studies. Cancer Sci. 2011 Jan 1;102(1):231–44.
  6. Yan L, Spitznagel EL, Bosland MC. Soy Consumption and Colorectal Cancer Risk in Humans: A Meta-Analysis. Cancer Epidemiol Biomarkers Prev. 2010 Jan 1;19(1):148–58.
  7. Dewell A, Weidner G, Sumner MD, Barnard RJ, Marlin RO, Daubenmier JJ, et al. Relationship of dietary protein and soy isoflavones to serum IGF-1 and IGF binding proteins in the Prostate Cancer Lifestyle Trial. Nutr Cancer. 2007;58(1):35–42.
  8. Nagata C, Shimizu H, Takami R, Hayashi M, Takeda N, Yasuda K. Dietary soy and fats in relation to serum insulin-like growth factor-1 and insulin-like growth factor-binding protein-3 levels in premenopausal Japanese women. Nutr Cancer. 2003;45(2):185–9.


About The Author

Cyrus Khambatta

Diagnosed with type 1 diabetes at the age of 22, I have spent over a decade learning the fundamentals of nutrition at the doctorate level. My goal is to share my knowledge of practical nutrition and fitness with people with prediabetes, type 1 and type 2 diabetes. Diabetes is an OPPORTUNITY to attain excellent health. Reversing the effects of insulin resistance can be a fun and enjoyable process if the right system is in place. That's why I've spent over 10 years developing a rock solid system that can minimize blood glucose variability and insulin resistance.

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