The issue is whether the fermentation of the soy beans negates the estrogen.
Dear Colleague
The effect of dietary phytoestrogens on estrogen-sensitive tumor proliferation is not yet scientifically documented. These issues should be considered in deciding whether to consume a nutrient:
1. The effect of the nutrient on tumor cell proliferation
2. The interaction of the nutrient with antineoplastic drugs
It is hypothesized that the phytoestrogens can have agonist or antagonist effects on estrogen receptors but these effects are related to the target tissue (eg. bone, breast, uterus, etc.), potency of the phytoestrogen, type of estrogen receptor in the tissue (ERa or ERB), duration of exposure to phytoestrogen and the dosage. Phytoestrogens were shown to have more affinity to ERB which is more abundant in bone tissue. Although phytoestrogens are of weak estrogenic effects and therefore have the potential of being an antagonist, but most of them are not documented to act as estrogen antagonist. Study findings are conflicting in this field. While some studies have shown prolipherative effect of phytoestrogens on estrogen-sensitive tumor cells, some others did not find any difference in the effect of phytoestrogens on estrogen-sensitive and non-estrogen-sensitive tumor cells. Even it is said that occasional consumption of phytoestrogens might result in increased proliferation of tumor cells.
Some studies showed a synergistic activity of Genistein with gemcitabine (an antineoplastic drug) on osteosarcoma. But the other possible nutrient-drug interactions are not yet documented.
In my opinion, if the patients is not exposed to high soy consumption before (eg. East Asian ethnicity) it might not be wise to advice a high risk patient consume natto in presence of conflicting findings and undocumented hypotheses.
You may also read these references for more information
Heather B. Patisaul and Wendy Jefferson. The pros and cons of phytoestrogens. Front Neuroendocrinol. 2010 October; 31(4): 400–419. doi: 10.1016/j.yfrne.2010.03.003
Zhang B, Shi ZL, Liu B, Yan XB, Feng J, Tao HM. Enhanced anticancer effect of gemcitabine by genistein in osteosarcoma: the role of Akt and nuclear factor-kappaB. Anticancer Drugs. 2010 Mar;21(3):288-96.
Leena Straussa, Risto Santtia, Niina Saarinena, Tomi Strenga, Suresh Joshia, Sari Mäkelä. Dietary phytoestrogens and their role in hormonally dependent disease. Toxicology Letters. Volumes 102–103, 28 December 1998, Pages 349–354.
Mark Frederick McCarty . Isoflavones made simple – Genistein’s agonist activity for the beta-type estrogen receptor mediates their health benefits. Medical Hypotheses. Volume 66, Issue 6, 2006, Pages 1093–1114
P Diela, S Schmidta, G Vollmer. Review In vivo test systems for the quantitative and qualitative analysis of the biological activity of phytoestrogens. Journal of Chromatography B. Volume 777, Issues 1–2, 25 September 2002, Pages 191–202
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