ABSTRACT
This chapter focuses on the isoflavones, but it is reasonable to deduce that the same general trends for bioavailability and metabolism will hold true for many flavonoids. The ability of isoflavones to exert their anticarcinogenic and other possible health effects depends upon their bioavailability, defined in a nutritional sense as the relative ability of these compounds to reach their sites of action in biologically active forms. Biliary excretion is likely the main limiting factor with respect to the dose percentage of isoflavones that is systemically available, meaning the proportion of the total dose that reaches the general circulation. Isoflavones in the human diet exist largely as glycosides. Isoflavone bioavailability depends upon the phenolic nature of these compounds, which determines their major metabolic products, the glucuronide and sulfate conjugates. Understanding the metabolism and bioavailability of these compounds is crucial to an appreciation of their potential as health protectants.
