In 2004 I wrote an unpublished meta-analysis paper investigating the potential protective mechanism of soy phytoestrogens and breast cancer. The conclusion was that “…the consumption of properly prepared fermented soy foods (miso, natto, tempeh) during adolescence appears to provide a chemoprotective effect later in life. Furthermore, sustained soy intake throughout life, both during adolescence and adulthood, may offer the most beneficial effects. However, there is no concrete evidence to suggest that soy or isoflavone consumption only during adult life is protective against breast cancer, although it may provide benefit to some women. The daily isoflavone dosage may factor into the protective effect as well with approximately 15g or two servings of traditional soy foods needed to offer any health benefit. Since intestinal bacteria produce equol adding fermented foods and probiotics to ones diet may realize better phytoestrogen benefits. Therefore, recommendations are for adults that enjoy soy to continue doing so at the suggested servings. For pre-pubescent and adolescent girls adding a couple of traditional soy food servings per day along with fermented foods and/or probiotics may reduce breast cancer risk later in life.
To understand the relationship between soy consumption, lifestyle differences, dosages, individuality and breast cancer, more research is necessary, particularly RCTs. The RCTs need to take into account “equol producers” to determine what, if any, dietary changes can increase equol production. Furthermore, research is needed on soy supplementation to evaluate its effectiveness and safety before it can be recommended as an addition to traditional soy foods.”
What does this all mean? The bottom line is that girls who at traditional soy foods during puberty appear to have protection against developing breast cancer. However there is tremendous amount of biochemical variation as it also depends on how much bacteria are produced in the gut. I also interpolate my conclusion to mean that probiotics (whether from pill or fermented foods) may offer a chemopreventative effect.
Please download my full research paper by clicking here. Soy and Breast Cancer
George Mandler
Licensed Acupuncturist & Nutritionist Dietitian
Acupuncture, Chinese Medicine, & Nutrition
Boston, Jamaica Plain, Cambridge, Massachusetts