ABSTRACT
Flavonoids have been the center of huge research interest over the past decade.1-6 They have been attributed to a wide range of beneficial properties regarding human health, including effects on cancer,7-16 cardiovascular diseases,14,17-19 atherosclerosis,20,21 inflammation,14,22 and other diseases in which oxidative stress has been implicated, such as the neurodegenerative disorders.3,23-26 A large number of in vitro studies have characterized flavonoids as powerful antioxidants against both reactive oxygen and reactive nitrogen species.4,27-32 Until recently, the ability of flavonoids to act as classical H-donating antioxidants was believed to underlie many of their reported health effects.10,11,18,21,33,34 However, the extent
of their antioxidant potential in vivo will be dependent on the absorption, metabolism, distribution, and excretion of these compounds within the body after ingestion and the reducing properties of the resulting metabolites. An understanding of the processes involved in the absorption and distribution of polyphenols is essential for determining their bioactivities in vivo and their significance. Recently, much data have accumulated on the biotransformation of flavonoids in the small intestine and gastrointestinal tract,14,35,35-42 as well as the hepatic metabolism.38,43,44 This chapter attempts to highlight the major sources of flavonoids in the human diet, draw attention to the main sites of biotransformation of flavonoids within the body, and emphasize the major metabolites that may exert biological activity in vivo.
