Polyphenols ubiquitously occurring in plant foods possess the beneficial effects on our health. The functions are classified into antioxidative potency and protein-function modulating activity. Antioxidative potency is an action eliminating reactive oxygen species and results in prevention of degenerative diseases. A bioavailable polyphenol in antioxidant potency is compound having ortho-diol (catechol) in the chemical structure. Protein function-modulating activity is a modulation of metabolic activity through the interaction with enzymes, membranous transporters, cellular or intracellular receptors, or signaling proteins. The target proteins depend upon the chemical stereosturucture of polyphenols. Phenylpropanoids can act on Nrf2-Keap1 system, flavones, flavonols and anthraquinones on arylhydrocarbon receptor and others, flavanones and isoflavones on estrogen receptor and others. These activities modify our body functions dynamically accompanying the prevention of degenerative diseases including cancers. On the other hand, most of phytochemicals when ingested, however, are removed by conjugation in the intestinal absorption processes. In order to find bioavailable polyphenols to play preventing roles in our body, chemicals that can escape the conjugation systems should be selected. A strategy for finding out the bioavailable polyphenols will also be discussed.

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