Many workers have postulated that diet and tumor development are related, and a considerable literature has developed on the possibility of altering the growth rate of tumors by dietary means (1–3). But in spite of a large number of experiments, usually performed with transplanted tumors, there appears to be no known dietary procedure by which the growth rate of a tumor can be altered once it has become firmly established, unless the diet be so grossly abnormal as to injure the host.
A more promising approach to the problem is a study of the effect of diet on the development of tumors induced by carcinogenic agents. The usual procedure consists of painting a large group of mice with tar, feeding them various diets, and then noting the time of appearance of the tumors (3–8). Using this technic, Maisin and co-workers have demonstrated the existence of both stimulating and inhibiting substances in animal tissue. The stimulating substances were found to be water-soluble, the inhibitory substances fat-soluble. Fairly potent concentrates of inhibitor were subsequently prepared from hog brain. Several workers (4, 6) have shown that a diet high in liver speeds up the rate of production of tumors induced by tar painting.