of Mammary Rats by

ABSTRACT-The development of mammary tumors was ex-amined in female noninbred Sprague-Dawley rats fed either a low-fat diet or high-fat diets containing different fats and fatty acid esters. Each rat was given 5 mg 7.12-dimethylbenz[a)anthracene by stomach tube 1 week before diets were introduced. Addition of 3 % ethyl oleate (an ethyl ester of an unsaturated fatty acid) to a diet high in saturated fat (coconut oil) had no significant effect on tumor development, but the addition of 3 % ethyl linoleate (an ethyl ester of a polyunsaturated fatty acid) increased the tumor yield to about twice that in rats fed either the high-saturated fat diet or a low-fat diet. Animals fed the high-saturated fat diet containing 3 % ethyl linoleate developed as many tumors as those fed a 20 % sunflower seed oil diet. though the sunflower seed oil diet contained about four times as much linoleate. Rats fed a high coconut oil diet containing 3 % menhaden fish oil. whic