Nutrient intakes: cancer causation and prevention.

High intakes of the macronutrients--proteins, lipids, and carbohydrates in the form of excess energy-have some cancer stimulating properties. On the contrary, epidemiologic and animal laboratory data indicate that high-level supplementation of some micronutrients--certain vitamins, minerals, and lipotropes, as well as some non-nutrients, most notably various types of dietary fiber, may be useful in the prevention of cancer. A wealth of data exists for macronutrients whereas most micronutrients are almost unstudied concerning their role in cancer prevention. Vitamins A, E, and C and selenium are the most well-studied micronutrients, and are recognized as effective with significant anticancer effects, at least in animal models. There are minimal data to suggest that some other micronutrients may also exert varying degrees of incidence reduction on one or more types of cancer. This is most true for folic acid, manganese, molybdenum, copper, the amino acids phenylalanine and methionine, and the lipotrope choline. Zinc and vitamins B1, B2, B6, B12 and pantothenic acid have even less data, and some data are contradictory. Therefore, it is premature to make recommendations concerning their usefulness in cancer prevention at present.