Intake of phytoestrogen foods and supplements among women recently diagnosed with breast cancer in Ontario, Canada.

Phytoestrogens are found in foods such as soy (isoflavones) and flaxseed (lignans), and certain botanical supplements. Their role in estrogen receptor positive (ER+) breast cancer recurrence and treatment is controversial, and it is unknown how this affects intake among patients. The Ontario Cancer Registry was used to identify 417 population-based breast cancer cases (mean time from diagnosis was 57 days). A questionnaire was mailed to determine intake of phytoestrogen foods and supplements in the last 2 mo, changes since diagnosis and differences by ER tumor status or hormonal treatment. Of 278 (67%) respondents, 56% consumed soy foods, 39% consumed isoflavone-rich foods (tofu, soybeans, soy milk, soy nuts), and 70% ate lignan-rich foods, including flaxseed (33%). Only soy milk, flaxseed, and flaxseed bread were commonly consumed more than once/wk. Few patients (4%) took isoflavone (soy, red clover, kudzu, licorice, isoflavones) or lignan/flaxseed supplements. Since diagnosis, 17% started or stopped soy foods (most stopped); this was more prevalent among those receiving hormonal treatment (20%; 95% confidence interval (CI): 14, 26) than not (6%; 95% CI: 1, 12). No other differences by ER status or hormonal treatment were observed. Research is needed to confirm this and to explore influencing factors.