Effect of the amount of dietary fat on the development of mammary tumors in BALB/c-MTV mice.

The relationship between dietary fat consumption and the incidence of breast cancer, if any, needs to be quantified so that dietary guidelines can be issued for the prevention of breast cancer. Frequently, only two widely different dietary fat levels, often differing in essential fatty acid content, have been compared in animal models. Moreover, the latent period in common animal models for breast cancer is very short and does not reflect the relatively long latent periods in human breast cancer. We describe a study with BALB/c-MTV mice, a strain with a high average tumor incidence and a latent period of over 60 weeks on average. The mice were fed diets with fat levels ranging from 10% to 40% of energy, in which fat was isocalorically substituted for carbohydrates. The level of linoleic acid in these diets was kept constant at 6.5% of energy. Both the mean tumor incidence and latent periods of the groups fed diets with 10-16% of energy as fat were not significantly different from each other. There were also no differences between these parameters in the groups fed 22-40% of energy as fat. However, the mean incidence and latent period of the groups fed 22% or more of energy as fat was significantly higher than that of the groups fed less fat. We conclude that above about 22% of energy, fat does not influence the incidence and latent period of mammary tumors in BALB/c-MTV mice.