Conversion of diets at tumor induction shows the pattern of tumor growth and metastasis of the first given diet.

In a previous study, significant differences in the growth rate of a transplantable mammary adenocarcinoma were observed between rats receiving a diet rich in saturated fatty acids (lard, diet A), and rats on a diet in which the saturated fat was partly replaced by polyunsaturated fatty acid of the omega-3 type (Menhaden oil, diet B). In the present investigation, it was our aim to study tumor growth in rats on diet A and B, as well as in rats that had, at tumor inoculation, a change of diets, from diet A to diet B. Tumor growth of rats receiving diet A throughout the whole experiment was the same as in those rats that had a conversion of diets. The data shows that the observed inhibiting effect of diet B on tumor growth could not be obtained when this diet was given exclusively after tumor inoculation.