Cancer preventive impact of naturally occurring, non-nutritive constituents in food

Numerous epidemiologic studies have shown that a diet rich in vegetables, fruits and fiber is associated with a decreased risk of cancer, particularly of epithelial tumors. Especially this association is evident for various citrus fruits, carrots, leafy green vegetables, as well as cruciferous- (sorts of cabbage, broccoli) and leak vegetables (garlic, onions, etc.). In the course of investigation of the protective mechanisms exerted by vegetable foodstuffs, a great number of secondary plant products such as carotenoids, sulfides, glucosinolates, plant sterols, saponins, terpens, phytoestrogens, flavones, protease inhibitors, or phenolic acids, which are substantial constituents of our daily food, have changed their meaning from a non-nutritive constituent to a probably cancer preventive biological-active substance. But also fermentable, soluble fibers and substances in fermented foods can exert protective effects on development of cancer. Mostly the anticarcinogenic action of biological-active substances is limited to an early stage of carcinogenesis. Therefore it seems to be important to start prevention of cancer by nutrition as early as possible and adhere to it over a long period.