Much has been written about the soy and breast cancer relationship. Initial interest in this relationship focused on the role that soy isoflavones may have in reducing the risk of developing breast cancer.1,2 But in the late 1990s, rodent research raised the possibility that soyfoods might worsen the prognosis of women with this disease.3 It wasn’t until 2009 that the first prospective observational study to address this concern showed that to the contrary, not only was post-diagnosis soy intake not harmful, it was associated with reduced risk of recurrence.4 Other studies from China concurred with that finding5,6 as did 2 U.S. cohort studies.7,8 Now, a Korean study can be added to this list.9
This prospective study included 606 women who filled out a dietary survey using a 24-hour recall within 3 years of breast cancer surgery. Women had a mean age of approximately 53.5 years and were followed for a mean of 89 months. During the follow up period, 61 women suffered a recurrence and 35 patients died.
A trained registered dietitian measured dietary intake using a structured 24-hour recall during the weekday to better reflect the patient’s usual dietary habits. If the patient had a special occasion on the day before the dietary survey, dietary intake of 48- hours before the dietary survey was measured. Fermented products were subdivided into three groups: fermented-soy, vegetable, and dairy products. Fermented soy products included Doenjang (long-term fermented soybean paste), Cheonggukjang (short-term fermented soybean paste), Kanjang (fermented soy sauce), and Gochujang (fermented red pepper paste). Women were divided into quartiles according to their fermented soy intake (g/d): ≤ 5.0, >5.0 to ≥15.0, >15.0 to ≥28.5, and >28.5.
When all women were included in the analysis, there was a dose response relationship between fermented soy intake and the likelihood of recurrence (Table 1). However, sub-analysis according to type of breast cancer revealed that fermented soy intake was inversely related to risk of hormone receptor positive breast cancer including both estrogen receptor (ER) positive and progesterone receptor (PR) positive breast cancer, more so than hormone-independent breast cancer. Although, the hazard ratios for intake quartile 4 were below 1.0 for both ER negative and PR negative breast cancer, the results were not statistically significant. Fermented soy intake was also inversely related to breast cancer-specific mortality.
Table 1. Adjusted hazard ratios* plus 95% confidence intervals for fermented soy intake and risk of recurrence
|Breast cancer||Quartile 1||Quartile 2||Quartile 3||Quartile 4||P for trend|
|All types||1.00 (reference)||0.592 (0.29, 1.20)||0.457 (0.22, 0.94)||0.336 (0.14, 0.78)||0.016|
|ER positive||1.00 (reference)||0.490 (0.20, 1.15)||0.130 (0.03, 0.57)||0.398 (0.11, 0.92)||0.012|
|ER negative||1.00 (reference)||2.173 (0.74, 6.32)||1.392 (0.50, 3.87)||0.257 (0.03, 2.19)||0.262|
|PR positive||1.00 (reference)||0.695 (0.29, 1.65)||0.497 (0.19, 1.30)||0.255 (0.07, 0.89)||0.019|
|PR negative||1.00 (reference)||0.760 (0.22, 2.55)||1.060 (0.38, 2.90)||0.553 (0.13, 2.22)||0.532|
There are several limitations to this study that warrant mention. One is that although the follow-up period was quite long, only 61 women suffered a recurrence. Two, total soy intake was not reported, only fermented soy intake was. However, most soy consumed in Korea is in unfermented form.10 It is difficult to speculate as to why unfermented soy was also not quantified although it may be that the impact of fermentation was the focus of this study more than soy per se because as noted previously, the dietary survey included questions about fermented vegetable and fermented dairy intake but not unfermented forms of these foods. Three, the isoflavone content of the soy products was not reported. However, according to the USDA database, miso (NDB, 16112) contains 41.45mg per 100g. If one uses the miso value as a guide, then the isoflavone cutoff for intake quartile 4 would be about 12 mg.
At least 10 health organizations have concluded that soyfoods can be safely consumed by breast cancer patients or that isoflavones don’t adversely affect breast tissue in postmenopausal women.11 The American Cancer Society12 and the World Cancer Research Fund International13 have concluded that post-diagnosis soy intake may improve the prognosis of breast cancer patients. This new study from Korea supports the positions of these organizations.9
Nevertheless, more research is needed to understand the impact of soy on the prognosis of breast cancer patients. However, given the observational data, and the other proposed benefits of soyfoods and their nutritional content, it is certainly reasonable for breast cancer patients to make soy a part of their diet.
1. Messina M, Barnes S. The role of soy products in reducing risk of cancer. J Natl Cancer Inst 1991;83:541-6.
2. Messina M, Messina V. Increasing use of soyfoods and their potential role in cancer prevention. J Am Diet Assoc 1991;91:836-40.
3. 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.
4. Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy food intake and breast cancer survival. JAMA 2009;302:2437-43.
5. Zhang YF, Kang HB, Li BL, Zhang RM. Positive effects of soy isoflavone food on survival of breast cancer patients in China. Asian Pacific journal of cancer prevention : APJCP 2012;13:479-82.
6. 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.
7. Caan BJ, Natarajan L, Parker B, Gold EB, Thomson C, Newman V, Rock CL, Pu M, Al-Delaimy W, Pierce JP. Soy food consumption and breast cancer prognosis. Cancer Epidemiol Biomarkers Prev 2011;20:854-8.
8. Guha N, Kwan ML, Quesenberry CP, Jr., Weltzien EK, Castillo AL, Caan BJ. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study. Breast Cancer Res Treat 2009;118:395-405.
9. Yang JB, Chung MS, Park YS. Association of fermented products with risk of cancer recurrence and mortality among breast cancer survivors: A prospective cohort study. Nutr Cancer 2023:1-11.
10. Kim Y, Kim DW, Kim K, Choe JS, Lee HJ. Usual intake of dietary isoflavone and its major food sources in Koreans: Korea National Health and Nutrition Examination Survey 2016-2018 data. Nutrition research and practice 2022;16:S134-S46.
11. Messina M, Duncan A, Messina V, Lynch H, Kiel J, Erdman JW, Jr. The health effects of soy: A reference guide for health professionals. Frontiers in nutrition 2022;9:970364.
12. Rock CL, Thomson CA, Sullivan KR, Howe CL, Kushi LH, Caan BJ, Neuhouser ML, Bandera EV, Wang Y, Robien K, et al. American Cancer Society nutrition and physical activity guideline for cancer survivors. CA Cancer J Clin 2022;72:230-62.
13. Becerra-Tomas N, Balducci K, Abar L, Aune D, Cariolou M, Greenwood DC, Markozannes G, Nanu N, Vieira R, Giovannucci EL, et al. Postdiagnosis dietary factors, supplement use and breast cancer prognosis: Global Cancer Update Programme (CUP Global) systematic literature review and meta-analysis. Int J Cancer 2023;152:616-34.
This blog is sponsored by SNI Global and U.S. Soy.