Anthocyanins are a class of polyphenols abundant in the skins of red grapes, and have been shown to have anti-cancer effects in models of colon cancer [Cooke et al. Int J Cancer 2006;119:2213-2220; Jing et al. J Agric Food Chem 2008;56:9391-9398]. Gut microflora metabolize anthocyanins to phenolic