ABSTRACT
Isoflavones are a subclass of the rather ubiquitous flavonoids but by comparison have a much more limited distribution in nature. The primary dietary sources of isoflavones are soybeans and soyfoods. It is often stated in the literature that many legumes and fruits and vegetables contain isoflavones; however, although these statements are technically correct they are misleading, because the amount in these foods is so small as to be nutritionally irrelevant.[1]
In contrast to many phytoallexins (substances that are formed by host tissue in response to physiological stimuli, infectious agents, or their products and that accumulate to levels that inhibit the growth of microorganisms), isoflavones are always present in significant quantities in soybeans, because one of their primary functions is to stimulate nodulation genes in soil bacteria called Rhizobium.[2] Rhizobia have the ability to induce the formation of nodules on soybean roots, which are required for the reduction of atmospheric nitrogen to ammonia, which the soybean can then use as a source of nitrogen for growth.
