Summation: which fat/how much fat--animals.

Promotion of carcinogenesis in rats by dietary fat depends on the amount and type of fatty acids ingested, mainly as triglycerides. A certain amount of essential fatty acid of the linoleate type (n-6) is required for promotion of mammary cancer and pancreatic cancer and probably also for colon cancer. Promotion is also enhanced by a high level of dietary fat, and this additional effect seems to be relatively independent of the type of fat. Saturated fatty acids, either medium or long chain, and cis and trans monoenoic fatty acids appear to have no specific promoting effects. Fish oils containing long-chain polyunsaturated fatty acids of the linolenate type (n-3) are inhibitory, and this may also be true for rapeseed oil high in erucic acid, a long-chain monoenoic fatty acid. The promoting action of dietary fat can be modified by other components of the diet, such as starch, sugar, and fiber. Promotion is also dependent on the length of time animals are exposed to the high-fat diet. The overall tumor yield can be decreased by reducing the level and degree of unsaturation of the dietary fat after a period of feeding a high polyunsaturated-fat diet.