Vegetables, fruit and cancer mechanisms 1991英文电子书.pdf

Cancer Causesand Control, 2, 427 - 442 REVIEW Vegetables, fruit, and cancer. II. Mechanisms Kristi A. Steinmetz and John D. Potter (Received 7March 1991;accepted in revisedform 23 May 1991) The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites was reviewed systematically in Part 1.1It was concluded that consumption of higher levels of vegetables and fruit is associated consistently, although not universally, with a reduced risk of cancer at most sites, and particularly with epithelial cancers of the alimentary and respiratory tracts. Possible mechan- isms by which vegetable and fruit intake might alter risk of cancer are addressed here. A large number of potentially anticarcinogenic agents are found in these food sources, including carotenoids, vitamins C and E, selenium, dietary fiber, dithiolthiones, glucosinolates and indoles, isothiocyanates, flavonoids, phenols, prot- ease inhibitors, plant sterols, allium compounds, and limonene. These agents have both complementary and overlapping mechanisms of action, including the induction of detoxification enzymes, inhibition of nitros- amine formation, provision of substrate for formation of antineoplastic agents, dilution and binding of car- cinogens in the digestive tract, alteration of hormone metabolism, antioxidant effects, and others. It appears extremely unlikely that any one substance is responsible for all the associations seen. Possible adverse effects of vegetable and fruit consumption are also examined. One way to consider the relationships reviewed here is to hypothesize that humans are adapted to a high intake of plant foods that supply substances crucial to the maintenance of the organism, but only some of which are currently called essential nutrients. Cancer may be