Similarity between frans Fat and Saturated Fat in the Modification of Rat Mammary Carcinogenesis1

Commercial hydrogénation of vegetable oils results in the introduction of frans fatty acids. In the present study, we have investigated the effect of feeding a fat which contained approxi mately 38% frans isomers (designated frans fat) on the induction of mammary tumors by dimethylbenz(a)anthracene in rats. The corresponding control fat (designated c/s fat), which had a similar fatty acid composition, consisted of only c/s isomers. Since both the frans and c/s fats were rather saturated, a comparison was also made between these 2 types of fat and com oil, which contains about 60% linoleic acid (Ci8.2)-Each fat was present in the diet at 2 levels, 5 and 20% by weight. Although rats fed the 20% frans fat or c/s fat diets had a slightly higher tumor incidence and yield than did those on the corresponding 5% fat control diets, the difference was not statistically significant. In contrast, rats fed the 20% com oil diet developed a much greater number of tumors than did rats fed a diet containing only 5% corn oil. Further analysis of the data showed that diets containing either frans fat or c/s fat were much less effective than were the corn oil diets in promoting the development of mammary neoplasia at either the 5 or 20% level. Our results thus suggest that frans fat behaves very much like a saturated fat in the modification of mammary tumorigenesis. A determination of the fatty acid con tent of the mammary fat pad indicated that its composition generally reflected the dietary fatty acid intake, with the incor poration of frans isomers into the mammary tissue found to be dependent on the quantity of frans fat in the diet.