Although most soy products, even TVP, have some genistein, it was discovered recently that miso has about twenty times as much genistein as unfermented soy foods, such as soy milk and tofu. Researchers at Tokyo's National Cancer Center Research Institute believe that during fermentation microbes cleave the bonds of genistein's processor molecule, converting it to the active anticancer substance. Other fermented soy foods, such as natto (fermented soybeans), also have higher levels of genistein than unfermented soy foods.

Several other studies have confirmed the fact that the fermentation of soybeans increases their concentration of isoflavones such as genistein and daidzein. When scientists in Taiwan compared the isoflavone content of dry soybeans to soybeans that had been fermented for just four months, they discovered that fermented soybeans contained much more isoflavones than dry, unfermented soybeans. Moreover, several years ago a group of scientists associated with the USDA compared the isoflavone content of a wide variety of foods and plants and reported in the Journal of Alternative Complementary Medicine that the isoflavone levels were relatively higher in fermented soy products such as soy miso. When they compared the genistein and daidzein levels of the same dry soybeans and fermented soybeans (soybean miso), the fermented soybeans had a 30 times higher concentration of these isoflavones!