Neutral fats and cancer.

High-fat diets enhance the development of mammary and intestinal tumors on animals, and dietary fat also shows a strong positive correlation with mortality from cancers of the breast and colon in human populations. In animals, dietary fat appears to act as a promoter of carcinogenesis rather than as an influence in the initiation of tumors. Polyunsaturated fats enhance mammary tumorigenesis and stimulate tumor growth more effectively than do saturated fats. However, diets containing a small amount of polyunsaturated fat and a high level of saturated fat increase mammary tumor yields as effectively as do diets containing a high level of polyunsaturated fat. Fatty acids of either the linoleate or linolenate family appear to be able to satisfy the small requirement for polyunsaturated fat. The mechanism by which dietary fat influences mammary tumorigenesis is not known but may involve hormonal effects, immune responses, to alterations in cellular membranes. Dietary fat is thought to enhance the development of intestinal tumors by stimulating production of bile acids, some of which act as promoters of tumorigenesis.