glucosides genistin, daidzin and glycitin are present in soybeans which are hydrolysed to their aglycone forms genistein, daidzein and glycitein respectively during soybean fermentation
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Tumor Proliferation Studies
Genistein, genistin, daidzein, and soy protein isolate containing different amounts of genistein have been shown to stimulate MCF-7 growth in ovariectomized athymic mice dose-dependently. The tumors regressed when mice were switched from genistein and genistein-enriched diet to a isoflavone-free diet. Furthermore, when similar amounts of genistein aglycone equivalents (750 ppm) were accompanied by differently processed soy foods, the stimulation of MCF-7 growth correlated inversely with the complexity of the soy product matrix (i.e., genistin > mixed isoflavones > isoflavone-rich soy extract Novasoy® > soy flour plus mixed isoflavones). However, the diet containing soy flour enriched with mixed isoflavones did not alter MCF-7 tumor growth in vivo even though the serum genistein levels were similar in all diet groups (Helferich et al., 2008). Also, daidzein was less effective in this model than genistein (Andres et al., 2011). Interestingly, plasma equol levels were highest in diets containing less processed soy. Because equol itself had no effect on the MCF-7 growth in vivo (Helferich et al., 2008; Andres et al., 2011), bacterial metabolism not related to equol formation might have been contributed. Yet, this thought has not yet been further pursued. Tumor growth stimulated by genistin and mixed isoflavone accompanied activation of the estrogen receptor α. In contrast, no stimulation of estrogen receptor α was observed in daidzein-induced tumor growth. Intraperitoneally injected biochanin A caused a growth delay of MCF-7 cells in vivo (Andres et al., 2011). However, the circumvention of intestinal metabolism impedes comparison with the results from feeding studies.