Written by Jessica Patella, ND. In a trial of 9,514 breast cancer survivors, women consuming over 10mg of soy isoflavones per day had a 36% reduced risk of recurrence.
There is a debate among health professionals about the benefits and side effects of eating soy, especially when related to breast cancer. This is mostly due to mixed research results and the various properties of soy (1-4). Soy has anti-cancer properties but also has estrogen-like properties, which can stimulate cells to replicate similar to cancer cells (1-4). A recent observational (cohort) study found that women diagnosed with breast cancer who consumed higher amounts of soy had a lower risk of death from breast cancer and breast cancer recurrence than women who consumed lower amounts of soy (1).
The research included 9,514 female breast cancer survivors who had a diagnosis of invasive breast cancer between 1991 and 2006. The research included women from two U.S. studies and one Chinese study (1). The women were followed for an average of 7.4 years and in that time, there were 1,171 deaths (78% from breast cancer, 7.7% cardiovascular disease, 6.2% other cancers, 8.4% other) and 1,348 recurrences of breast cancer (1).
Soy food intake was evaluated by food questionnaires and 24-hour dietary recalls by phone (1). The average intake of soy in US women (3.2 +/9.8 mg/ per day) was much lower than in Chinese women (45.9 +/- 38.3 mg per day) (1). Both U.S. and Chinese women with higher intakes of soy also were more likely to exercise and eat more cruciferous vegetables (broccoli, brussels sprouts, etc). In the US specifically, women with higher intakes of soy were also more likely to have lower body mass indices, be highly educated and be current nonsmokers (1).
Despite the large difference in types of soy food intakes between China and the US, women who consumed greater than or equal to 10 mg of soy (isoflavones) per day, compared to women who consumed 4 mg per day or less, had a 29% reduced risk of dying from breast cancer and a 36% reduce risk of recurrence (HR 0.71; 95%CI 0.52, 0.97 and HR 0.64; 95%CI 0.50, 0.82 respectively) (1).
Women who were taking the drug tamoxifen (with estrogen receptor-positive tumors) and consumed greater or equal to 10 mg of soy (isoflavones) per day had a 37% reduced risk of recurrence compared to women who consumed less than 4 mg per day of soy (HR 0.63; 95%CI 0.46, 0.87) (1).
There are a few weaknesses in the study. Because higher levels of soy intake were also associated with women who had healthier lifestyle factors (exercise, increased vegetable consumption, lower weight & non-smokers), it is possible those factors also played a role (1). It is also possible that the food questionnaires were not completely accurate representations of total soy intake, since questionnaires were based on the participants’ ability to recall what they had consumed previously (1).
In conclusion, soy intake of greater than or equal to 10 mg per day was associated with a reduced risk of death from breast cancer and a reduced risk of breast cancer recurrence when compared to women who consumed less than 4 mg of soy per day (1). This was the largest study of its kind to date (1).
Jessica Patella, ND, is a naturopathic physician specializing in nutrition and homeopathic medicine and offers a holistic approach to health. She earned her ND from Southwest College of Naturopathic Medicine in Tempe, AZ, and is a member of the North Carolina Association of Naturopathic Physicians. Visit her website at www.awarenesswellness.com.
Source: Nechuta, Sarah J., et al. “Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women.” The American journal of clinical nutrition 96.1 (2012): 123-132.
© 2012 American Society for Nutrition
Posted May 9, 2013.
References:
- Nechuta SJ, et al. Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women. Am J Clin Nutr 2012; 96:123-32.
- Hilakivi-Clarke L, et al. Is soy consumption good or bad for the breast? J Nutr 2010; 140:2326S–34S.
- Trock BJ, et al. Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst 2006; 98:459–71.
- Taylor CK, et al. The effect of genistein aglycone on cancer and cancer risk: a review of in vitro, preclinical, and clinical studies. Nutr Rev 2009;67:398–415.
