Safety of Soyfoods and Breast Cancer

By Meghan Malka

Woman eating Edamame (istock)

Soyfood consumption and the risk of breast cancer has been a controversial topic.  And this Breast Cancer Awareness Month, we’re here to share the current research, which has found that eating soyfoods is safe for both healthy individuals as well as breast cancer survivors.  The science shows soyfood consumption is not linked with developing breast cancer or breast cancer recurrence, and, in reality, soyfood consumption has been linked to a reduction in breast cancer risk.

The American Cancer Society says, “For the breast cancer survivor, current research finds no harmful effects from eating soy foods. These foods may even help tamoxifen work better.”

Another top cancer-fighting association, the American Institute for Cancer Research, reviewed all the latest research in 2012 and maintained its stance that soyfoods are not only safe but “contain several key nutrients and phytochemicals studied for their cancer prevention properties.”

Myth Buster

Myth: Soyfoods are not safe for women at risk of developing breast cancer or breast cancer survivors because they contain estrogen.

Truth: Research shows that women who are at risk for developing breast cancer or who are breast cancer survivors can safely consume moderate amounts of soyfoods.  A review of more than 130 human research trials and meta-analyses published in peer-reviewed journals since 1998(1-6) indicates that soyfoods do not cause tumors in breast tissue and do not have significant effects on those at risk of getting breast cancer.

Hearing conflicting messages in the media can be confusing, but it’s important to look at the science.  Human research trials have not demonstrated any link between eating soyfoods and tumor growth.  Where the conflicting information comes from are a couple studies done on animals that have indicated soy might increase the chances of breast cancer recurrence because soy contains isoflavones.(7,8) Isoflavones are often described as phytoestrogens because they are found in plants (phyto) and are structurally similar to human estrogens. Isoflavones are much weaker than naturally circulating human estrogens, as they have approximately 1/1000th the biological activity of circulating human estrogens, and therefore do not have estrogen-like effects in humans.  Furthermore, the levels of isoflavones given to mice in these studies were at enormously higher than levels found in traditional soyfoods.  People who eat a balanced diet rich in soyfoods would not come close to consuming isoflavone levels as high as those used in these experiments on animals.

Soyfoods are safe for breast cancer survivors. Soyfoods do not appear to increase the risk of breast cancer recurrence among survivors of the disease. (9-17) The American Cancer Society recommends that breast cancer survivors can safely consume moderate amounts of soyfoods – anywhere from a few servings per week to 3 servings per day.(17)

Soyfoods may reduce the risk of developing breast cancer. Research has found that women who eat soyfoods regularly are less likely to develop breast cancer, compared to those who don’t.  Soyfoods consumption may reduce the risk of breast cancer especially when soy is consumed during childhood and adolescence.(18-20)

Researchers at the University of Southern California found women averaging one cup of soymilk or about one-half cup of tofu daily have a 32% less risk of developing breast cancer and a 29% decreased risk of death, compared with women who ate little or no soyfoods.(21)

Breast cancer is a very complex disease and risk may be dependent on multiple factors.  As always, it is important to eat a healthy diet, get physical activity and maintain medical checks for overall health and breast cancer prevention.

Links worth checking out

 

As always be sure to check us out on Facebook, Twitter and Pinterest for more great recipes and interesting facts about soyfoods. Check out our YouTube page featuring with videos hosted by food and nutrition expert Rebecca Scritchfield, RD.

My name is Meghan.  I have a Masters of Public Health in Nutrition from the University of North Carolina and I will soon acquire the Registered Dietitian license.  So you could say I am an “RD to be.”  You can be sure that all of the information here is based on scientific research and in line with the recommendations of national health organizations and agencies.  We bring you the science, connect you to the recipes and so let us know what you like and what you want to know.

 

References

1. Maskarinec G, Morimoto Y, Conroy SM, Pagano IS, Franke AA. The volume of nipple aspirate fluid is not affect by 6 months of treatment with soy foods in premenopausal women. J Nutr 2011;141:626-30.

2. Maskarinec G, Takata Y, Franke AA, Williams AE, Murphy SP. A 2-year soy intervention in premenopausal women does not change mammographic densities. J Nutr 2004;134:3089-3094.

3. Brown BD, Thomas W, Hutchins A, Martini MC, Slavin JL. Types of dietary fat and soy minimally affect hormones and biomarkers associated with breast cancer risk in premenopausal women. Nutr Cancer. 2002;43:22-30.

4. Verheus M, van Gils CH, Kreijkamp-Kaspers S, Kok L, Peeters PH, Grobbee DE, van der Schouw YT. Soy protein containing isoflavones and mammographic density in a randomized controlled trial in postmenopausal women. Cancer Epidemiol Biomarkers Prev. 2008;17:2632-2638.

5. Ward HA, Kuhnle GGC. Phytoestrogen consumption and association with breast, prostate and colorectal cancer in EPIC Norfolk. Arc of Biochem and Biophys. 2010;501:170-5.

6. Dijkstra SC, Lampe JW, Ray RM, Brown R, Wu C, Li W, Chen C, King IB, Gao D, Hu Y, Shannon J, Wa¨ha¨ la¨ K, Thomas DB. Biomarkers of dietary exposure are associated with lower risk of breast fibroadenomas in Chinese women. J Nutr. 2010;140:1302-10.

7. Hsieh CY, Santell RC, Haslam SZ, Helferich WG. Estrogenic effects of genistein on the growth of estrogen receptor-positive human breast cancer (MCF-7) cells in vitro and in vivo. Cancer Res 1998 ; 58 : 3833

8. Allred CD, Ju YH, Allred KF, Chang J, Helferich WG. Dietary genistin stimulates growth of estrogen-dependent breast cancer tumors similar to that observed with genistein. Carcinogenesis 2001 ; 22 : 166773.

9. Nechuta S, Caan B, Chen W, Lu W, Chen Z, Kwan ML, Flatt SW, Zheng Y, Zheng W, Pierce JP, Shu XO. Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of compbined evidence from cohort studies of US and Chinese women. Amer J Clin Nutr. 2012;96:123-132.

10. Dong JY, Qin LQ. Soy isoflavones consumption and risk of breast cancer incidence or recurrence: a meta-analysis of prospective studies. Breast Cancer Res Treat. 2011;125:315-23.

11. Cho Y, Kim J, Park KS, Kim SY, Shin A, Sung MK, Ro J. Effect of dietary soy intake on breast cancer risk according to menopause and hormone receptor status. Eur J Clin Nutr. 2010;64:924-32.

12. Kang X, Zhang Q, Wang S, Huang X, Jin S. Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy. CMAJ. 2010;182:1857-62.

13. Iwasaki M, Hamada GS, Nishimoto IN, Netto MM, Motola J, Laginha FM, Kasuga Y, Yokoyama S, Onuma H, Nishimura H, Kusama R, Kobayashi M, Ishihara J, Yamamoto S, Hanoaka T, Tsugane S. Dietary isoflavone intake and breast cancer risk in case-control studies in Japanese, Japanese Brazilians, and non-Japanese Brazilians. Breast Cancer Res Treat. 2009;116:401-411.

14. Zhang CX, Ho SC, Cheng SZ, Chen YM, Fu JH, Lin FY. Effect of dietary fiber intake on breast cancer risk according to estrogen and progesterone receptor status. Eur J Clin Nutr. 2011;65:929-36.

15. Horn-Ross PL, John EM, Lee M, Stewart SL, Koo J, Sakoda LC, Shiau AC, Goldstein J, Davis P, Perez-Stable EJ. Phytoestrogen consumption and breast cancer risk in a multiethnic population. Am J Epidemiol. 2001;154:434-441.

16. Wang Q, Li H, Tao P, Wang YP, Yuan P, Yang CX, Li JY, Yang F, Lee H, Huang Y. Soy isoflavones, CYP1A1, CYP1B1, and COMT polymorphisms, and breast cancer: A case-control study in southwestern China. DNA Cell Biol. 2011;30:585-9

17. American Cancer Society. Nutrition and Physical Activity During and After Cancer Treatment: Answers To Common Questions. Accessed Oct. 1, 2013 at http://www.cancer.org/treatment/survivorshipduringandaftertreatment/nutritionforpeoplewithcancer/nutrition-and-physical-activity-during-and-after-cancer-treatment-answers-to-common-questions?sitearea=MH

18. Trock BJ, Hilakivi-Clarke L, Clarke R. Meta-analysis of soy intake and breast cancer risk. J Nat Cancer Inst. 2006;98:459-71

19. Yan L, Spitznagel E. A meta-analysis of soy foods and risk of breast cancer in women. Int J Cancer Prevention 2005;1:281-293.

20. Shu, X, Zheng, Y, Cai H, et al Soy Food Intake and Breast Cancer Survival. JAMA. 2009;302(22):2437-2443.

21. Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008;98:9-14.

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