The role of nutrients in cancer causation.

The role of nutrients in cancer causation has been a subject of considerable interest, research, and public discussion in recent years. Results from epidemiologic, clinical, and animal studies have suggested that: 1) a reduction in total calories decreases risk for a number of tumor types; 2) dietary protein is directly correlated with liver, prostate, and colon cancer, among others, with increasing dietary protein increasing the risk; 3) increased dietary fat is correlated with increased risk for breast cancer; the evidence for an effect of fat on colon cancer is equivocal in human and animal studies; 4) a deficiency of vitamin A may enhance lung and colon tumors in animal experiments but in human this is equivocal. Increasing vitamin A above normal levels, as an anticarcinogenic effect, has not been satisfactorily demonstrated in animal models. The synthetic retinoid, 13-cis retinoic acid, inhibits both colon and lung cancer in animal models; 5) zinc deficiency is associated with enhanced esophageal cancer in humans and markedly enhances animal tumors; selenium inhibits this form of neoplasia in animals, 6) diets low in lipotropes enhance liver cancer induced by a variety of hepatocarcinogens. Our data from studies in animal models agree in some cases with epidemiological observations, but disagree with others, particularly fat and colon cancer. Overall, some forms of cancer are enhanced by excessive calories, increased dietary protein and fat, and by deficiencies of vitamin A, selenium, zinc, and lipotropes. Decreasing total intake of calories, protein, and fat, and ensuring adequate dietary levels of vitamin A, selenium, zinc, and lipotropes decreases risk for some forms of cancer.