The influence of dietary levels of vitamin A and fat on colon cancer.

Rats fed diets high (24%) or low (5%) in fat were given dietary levels of vitamin A (retinyl acetate) ranging from 0.3 to 30 micrograms/g food. The lowest tumor incidence was in the group fed diets high in vitamin A and low in fat. When the diet was high in fat and low in vitamin A, tumor incidence and frequency were significantly increased over that in rats fed the high-fat diet with normal levels of vitamin A (10 micrograms/g feed). However, even with a high level of fat in the diet, raising the level of vitamin A above 10 micrograms/g feed had no further beneficial effect. Thus, although there was a significant interaction between vitamin A and fat, it is the latter that appears to require the most attention, once the vitamin A intake is adequate. These data support the view that we should set as a goal an adequate, diversified diet that is low in fat but that an excessive intake of vitamins such as vitamin A that are toxic should be avoided.