A standardized freeze-dried preparation of desiccated table grapes containing polyphenols (including flavanols, anthocyanins, flavonols, and stilbenes such as resveratrol) and other unidentified compounds with antioxidant activity. Standardized freeze-dried table grape powder increases serum antioxidant activity and reduces the macrophage-mediated oxidation and uptake of low-density lipoprotein (LDL). This agent has been shown to inhibit genes linked to the development of sporadic colorectal cancer and may exhibit chemopreventive activity for other human cancers.