Dietary fat, immunological response, and cancer in rats.

lmmunocompetence can be modified by dietary means. Quality and quantity of fat have been associatedwith differ ences in tumor induction and immunological response in ani mals, and epidemiobogical observations have indicated that certain dietary lipids are associated in some obscure way with changes in tumor incidence in human populations. Data pre sented at this Workshop indicate that dietary fats are associ ated with an enhancement of cancer of the breast, prostate, and colon in human populations and with cancer of the breast and possibly the liver in animal models. Polyunsaturated fats are more enhancing, but cholesterol, other dietary sterols, and their degradation products appear to influence cancer induc tion either directly or indirectly. Fats appear to be involved in promotion rather than initiationof the carcinogenesis process. That this is not established, however, indicates that an immu nobogicalmechanism may be involved in these phenomena. Quality and quantity of dietary fat influence lipid metabolism and sterol synthesis. Obesity depresses immune functions, and further, Is involved in some obscure manner with endometrial cancer in women. Lipemia is associated with aberrations of immune function in people; polyunsaturated fats (a) decreased rejection crisis in renal transplant patients and (b) suppressed delayed hypersensitivity to skin tests in cancer patients and control subjects with evidence for a regulatory role by unsatu rated fats on lymphocyte reactivity, possibly through effects on prostaglandinsand hormone synthesis. The oxidation products of cholesterol exhibit profound effects over some aspects of immune response, and plasma lipoproteins and their subjects are involved in some manner with immunoregulatory aspects of lymphocytes, inhibiting in vivo and in vitro functions. Clearly, dietary and endogenous lipids influence immunocompetence and, in this manner, probably susceptibility to cancer.