Soyfoods Association of North America

1050 17th Street, NW • Suite 600 • Washington, DC 20036 • USA

Standby Statement on Soy Protein and Genes Linked to Breast Cancer

Soyfoods are part of a healthy diet and Americans combine soy protein-based foods with animal proteins and other plant proteins from legumes, grains and nuts in their daily diets. One bioactive component of soy protein containing foods is a phytoestrogen, known as isoflavone. Mean isoflavone intake for the average U.S. person is only 2.35 mg/day, about the amount from one ounce of soymilk, calculated using the USDA database and the National Health and Nutrition Examination Survey (NHANES) III 24-h dietary recall.[1] The total mean intake of isoflavones in Asian countries ranges from 25 to 50 mg/d, with a small proportion (10%) consuming as much as 100 mg/d.[2] Japanese women have historically had very low rates of breast cancer.

Researchers at the Sloan Kettering Cancer Center have recently reported that 52 grams of soy protein isolate with an average of 104 mg isoflavones consumed daily for a duration ranging between a minimum of 7 days to a maximum of 30 days by women with diagnosed breast cancer may increase expression of genes related to cell proliferation and tumorgenic growth factor, but there was no recorded growth in the tumor cells. Jacqueline Bromberg, co-author of the study, even stated the limitations of the study when saying: “Although the genes were being expressed, it is not clear that this will translate into actual tumour growth. But the concern is that there may be the potential.”

The soy supplemented group had higher plasma isoflavones which was correlated to changes in multiple genes in breast tissue from women; however, the researchers did not clearly describe why they concluded that these over-expressed genes would have an adverse effect. Additional assays would be needed in order to make such conclusions. Soyfoods and soy-protein containing foods confer some benefit to lowering the risk of certain chronic diseases as part of low cholesterol, low saturated fat diets; but soyfoods or soy protein are not medicines and would not normally be used as medicinal treatments for women with breast cancer. The most promising research suggests there is a protective effect against development of breast cancer when soy protein containing foods are consumed early in life and throughout puberty[3],[4],[5],[6],[7].

The American Institute for Cancer Research reviewed the latest scientific evidence on soy and cancer in 2012, and released a position statement[8] that soyfoods are not only safe but “contain several key nutrients and phytochemicals studied for their cancer prevention properties.” The American Cancer Society reiterates this statement and supports soyfood consumption.[9]

[1] Bai W, Wang C, Ren C. Intakes of total and individual flavonoids by US adults. Int J Food Sci Nutr. 2013 Sep 11.

[2] Messina M, Nagata C, Wu AH. Estimated Asian adult soy protein and isoflavone intakes. Nutr Cancer. 2006;55:1–12.

[3] Warri A, Saarinen NM, Makela S, Hilakivi-Clarke L. The role of early life genistein exposures in modifying breast cancer risk. Br J Cancer. 2008;98:1485–93.

[4] Korde LA,Wu AH, Fears T, Nomura AMY,West DW, Kolonel LN, Pike MC, Hoover RN, Ziegler RG. Childhood soy intake and breast cancer risk in Asian American women. Cancer Epidemiol Biomarkers Prev. 2009;18:1050–9.

[5] Lee SA, Shu XO, Li H, Yang G, Cai H, Wen W, Ji B-T, Gao J, Gao YT, Zheng W. Adolescent and adult soy food intake and breast cancer risk: results from the Shanghai Women’s Health Study. Am J Clin Nutr. 2009;89:1920–6.

[6] Shu X-O, Jin F, Dai Q, Wen W, Potter JD, Kushi LH, Ruan Z, Gao YT, Zheng W. Soyfood intake during adolescence and subsequent risk of breast cancer among Chinese women. Cancer Epidemiol Biomarkers Prev. 2001;10:483–8.

[7] Wu AH, Wan P, Hankin J, Tseng C-C, Yu MC, Pike MC. Adolescent and adult soy intake and risk of breast cancer in Asian-Americans.Carcinogenesis. 2002;23:1491–6.

[8] http://www.aicr.org/foods-that-fight-cancer/soy.html#sthash.IFQzu4Kb.dpuf

[9] http://www.cancer.org/search/index?QueryText=soybean#sthash.IFQzu4Kb.dpuf