Antioxidant Phytochemicals in Fruits and Vegetables: Diet and Health Implications

Abstract

Received for publication 26 May 1999. Accepted for publication 10 Aug. 1999. Mention of a trade name, proprietary product ,or specific equipment does not constitute a guarantee by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. To whom reprint requests should be addressed (phone: (617) 556-3311; fax: (617) 556-3299; e-mail: prior@hnrc.tufts.edu). Increased consumption of fruits and vegetables has been associated with protection against various age-related diseases (Ames et al., 1993; Steinberg, 1991). What dietary constituents are responsible for this association is not known, but well-characterized antioxidants, including vitamins C and E, or β-carotene, are often assumed to contribute to the observed protection (Ames et al., 1993; Buring and Hennekens, 1997; Gey et al., 1991; Stahelin et al., 1991; Steinberg, 1991; Willett, 1994). However, the results from intervention trials have not been conclusive regarding the protection following supplementation with such antioxidants (Hennekens et al., 1996; Omenn et al., 1996; Prieme et al., 1997; Van Poppel et al., 1995). Recent epidemiological evidence indicates that the putative beneficial effects of a high intake of fruits and vegetables on the risk of diseases of aging may not be exclusively due to these antioxidants (Hertog et al., 1992; Knekt et al., 1997), but other antioxidant phytochemicals contained in fruits and vegetables may be equally important. To critically evaluate the potential roles of these phytochemicals in prevention of agerelated diseases, we will discuss the free radical or oxidative stress theory of aging and present data on the antioxidant capacities of fruits, vegetables, and their phytochemical components, mainly flavonoids. Reports on the absorption of these flavonoids and the effects of fruit and vegetable intake on the antioxidant status in humans will be reviewed.