The role of dietary factors in prevention of chemically-induced cancer was reviewed on two models: i) the role of high fiber diets in prevention of colon cancer and ii) the role of high fat diets in prevention of mammary gland cancer, i) Experiments in colon cancer showed that 20% cellulose content decreased tumor incidence caused by 1,2-dimethylhydrazine (DMH) to 33% compared with 92% of tumors developed in animals fed a fiber-free diet. The tumor-preventive effect of a cellulose diet was accompanied by increased enzyme concentrations, such as ornithine decarboxylase, thymidine kinase and beta-glucuronidase. Corncob fiber (15%), treated with the fungus Pleurotus os., had a significant protective effect against DMH-induced rat colon cancer. This effect was accompanied by activation of some cellular mechanisms, i.e. apoptosis, proliferating cell nuclear antigen (PCNA) and p53 protein synthesis. A high positive correlation was found between tumor grade and p53 protein in the serum (r=0.97) or in the cell cytoplasm (r=0.77), and between tumor grade and PCNA (r=0.81). An inverse relationship was found between tumor grade and apoptosis (r=-0.63). ii) Experiments in mammary gland cancer showed that a 15% olive-oil diet reduced tumor incidence caused by 9,10-dimethyl-1,2-benzanthracene to 30%, compared with 55% in the control group. The antitumor effect of the olive oil diet was connected to its content of monounsaturated fatty acids, such as oleic and palmitic acids. The promotive tumorigenic effects of other high-fat diets (avocado, soybeans) were associated with high content of some polyunsaturated fatty acids (linoleic and alpha-linolenic). We concluded that different diets have different targets. The effect of the same diet depends on its content of anti-tumor substances.

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