Phytoestrogens in soy: a tentative protective factor against breast cancer

Background: Breast cancer is the most highly diagnosed cancer among women in the world, accounting for almost 1.7 million new cases diagnosed in 2012. The investigation of soy’s role in the prevention of breast cancer arose from the significant differences in breast cancer incidence between American women and Asian women. One key difference observed between these two populations is the amount of soy consumed: Asian women are reported to consume a mean daily intake of 10-50g of soy, while American women are reported to consume a mean daily intake of 1-3g of soy. Soy isoflavones, the third main class of phytoestrogens, merit grounds for investigation in breast cancer research as they are structurally similar to estrogen hormone, estradiol, and pose agonist and antagonist effects on estrogen receptors.\ud Objectives: The purpose of this research is to evaluate the literature and investigate whether the ingestion of phytoestrogens found in soy products decreases a woman’s risk of developing breast cancer.\ud Methodology: A search of the JNCI, Google Scholar, and Pubmed was conducted using search terms such as: soy, phytoestrogens, tofu, isoflavones, genistein, daidzein, premenopausal, asian, caucasian, women, and breast cancer. The final search was evaluated and narrowed down to six articles published between December 1998 and 2013, which were selected for review and use in this abstract assignment. Meta-analyses, observational studies, and experimental case-controlled studies were reviewed. Only full-length original journal articles were considered for review. Results: Estimations of risk, levels and measures of soy, and control of confounding variables varied considerably across studies. While non-fermented soy products tended either to show no association or an inverse association with the development of breast cancer, contrasting studies showed that isoflavones, particularly genistein, in soy products stimulate the proliferation of breast tumours in premenopausal women. Fermented soy products, such as miso, showed little effect at all. While the intake of soy isoflavones among Asian populations was associated with a decreased risk of breast cancer, the opposite was true for Western populations.\ud Conclusions: As a result of the heterogeneity present in study designs, it is unclear whether phytoestrogens in soy have a preventative or stimulatory effect on the development of breast cancer in women. More long-term prospective cohort studies are needed to evaluate the relationship between phytoestrogens and breast cancer risk