Comparative effects of milk, yogurt, butter, and margarine on mammary tumorigenesis induced by 7,12-dimethylbenz(a)anthracene in rats.

The effects of margarine and butter on mammary tumorigenesis were compared in the first experiment. Altering the levels of dietary margarine and butter influenced the development of mammary tumors induced with 7,12-dimethylbenz(a)anthracene (DMBA) in rats. Margarine enhanced tumorigenesis dose dependently in both the incidence and the number of mammary tumors. On the other hand, butter that was substituted for margarine did not show any enhancing effects. Inasmuch as butter is made from cow's milk, the effect of cow's milk was studied in the second experiment. It was expected that milk might inhibit mammary tumorigenesis. Contrary to our expectations, however, milk and yogurt did not inhibit but enhanced the DMBA-induced mammary tumorigenesis. It remains to be elucidated whether the enhancing effect was caused by some specific factors in milk or by the difference in energy or nutrient intakes.