Complex sentence: Nattō contains chemicals alleged to prevent cancer, for example, daidzein, genistein, isoflavone, phytoestrogen, and the chemical element selenium, however, most of these chemicals also may be found in other soybean products, and their effect on cancer prevention is uncertain.
Split into simpler sentences: Nattō contains chemicals alleged to prevent cancer, for example, daidzein, genistein, isoflavone, phytoestrogen, and the chemical element selenium. However, most of these chemicals can also be found in other soybean products, and their effect on cancer prevention is uncertain.