Soy Foods for Breast Cancer Survivors and Women at High Risk for Breast Cancer?

Abstract

Soybeans, grown in East Asia for thousands of years, only arrived in the United States 150 years ago ( 1 Smil V. Magic beans. Nature. 2000; 407: 567 Google Scholar ). Common preparations include boiled green immature soybeans, soy milk, tofu (curd made from soy milk), flour from mature seeds, and fermented products such as miso, natto, and tempeh. Modern processing has led to the production of hundreds of new foods from soy protein, including meat alternatives, flavored and sweetened soy milks, dairy substitutes, powdered soy beverages, and energy bars ( 2 Soy Foods Association of North America. Soyfood Sales and Trends. Available at: http://www.soyfoods.org/sales/sales.html. Accessed June 15, 2005. Google Scholar ). In addition, soy protein isolates and isoflavones are marketed as dietary supplements. Based on their estrogen-like structure and properties, it was proposed that isoflavones may be the active ingredients of soybeans and protect against hormone-dependent cancers ( 3 Messina M. Barnes S. The role of soy products in reducing risk of cancer. J Natl Cancer Inst. 1991; 83: 541-546 Google Scholar , 4 Adlercreutz H. Phyto-oestrogens and cancer. Lancet Oncol. 2002; 3: 364-373 Google Scholar ), prevent osteoporosis ( 5 Sirtori C.R. Risks and benefits of soy phytoestrogens in cardiovascular diseases, cancer, climacteric symptoms and osteoporosis. Drug Saf. 2001; 24: 665-682 Google Scholar ), and alleviate menopausal symptoms without the side effects of hormone replacement therapy ( 6 Kurzer M.S. Phytoestrogen supplement use by women. J Nutr. 2003; 133: S1983-S1986 Google Scholar ). Breast cancer survivors and women at high risk of developing the disease have been exposed to conflicting recommendations with regard to soy supplementation. Whereas the potential benefits of soy are strongly publicized by claims and promises in the popular press, the Internet, and health food stores, some professionals express concerns that soy foods may be harmful to certain individuals. The American College of Obstetricians and Gynecologists states, “Although the mechanisms of action of soy and dietary isoflavones are not fully understood, they seem to involve binding to the estrogen receptor. For this reason, one should not assume that these dietary supplements are safe for women with estrogen-dependent cancers, most importantly breast cancer” ( 7 The American College of Obstetricians and Gynecologists. Use of Botanicals for Management of Menopausal Symptoms. Available at: http://www.acog.org/from_home/publications/misc/pb028.htm. Accessed June 15, 2005. Google Scholar ). The increasing soy consumption, a growth in sales from $300 million to $3.9 billion over 11 years ( 2 Soy Foods Association of North America. Soyfood Sales and Trends. Available at: http://www.soyfoods.org/sales/sales.html. Accessed June 15, 2005. Google Scholar ), has led to continuous soy exposure of adult populations that had consumed little soy earlier in life. According to marketing research, up to one quarter of Americans now eat soy foods once per week or more ( 2 Soy Foods Association of North America. Soyfood Sales and Trends. Available at: http://www.soyfoods.org/sales/sales.html. Accessed June 15, 2005. Google Scholar ). The authorization of the “soy protein and coronary heart disease” health claim by the Food and Drug Administration in 1999 contributed to this increase and, if approved, a health claim for cancer risk reduction that is currently under review by the Food and Drug Administration may further popularize soy foods ( 8 Solae LLC, submitter. 2004Q-0151: Qualified Health Claim (QHC): Soy Protein and Cancer. Available at: http://www.fda.gov/ohrms/dockets/dockets/04q0151/04q0151.htm. Accessed September 3, 2004. Google Scholar ). The potential for breast cell stimulation by isoflavones is a source of concern for many women, health professionals, and in particular, for breast cancer survivors who seek alternatives to conventional hormone replacement therapy ( 9 Messina M.J. Loprinzi C.L. Soy for breast cancer survivors A critical review of the literature. J Nutr. 2001; 131: S3095-S3108 Google Scholar ). This commentary discusses a number of issues that are relevant to these divergent opinions. Although the distinction is not always straightforward, the focus will be on soy foods defined as “any substance that can be metabolized by an organism to give energy and build tissue” as opposed to dietary supplements, which, according to the Food and Drug Administration, are “products that contain one or more vitamins, minerals, herbs or other dietary substances ingested in pill, capsule, tablet, or liquid form” ( 10 US Food and Drug Administration, Center for Food Safety and Applied Nutrition. Dietary Supplement Health and Education Act of 1994. Available at: http://www.cfsan.fda.gov/∼dms/dietsupp.html. Accessed June 22, 2005. Google Scholar ). G. Maskarinec is an associate researcher, Cancer Etiology Program, Cancer Research Center of Hawaii, Honolulu