Influence of diet upon the neoplastic diseases of the rodent.

The relationship between tumor incidence and diet, in rodents, has been studied for several decades including the effects of total intake, calorific values and individual components. There is variation with the species and strain of animal used, but in general over nutrition has been shown to promote tumor development. The influence of diet upon the neoplastic diseases occurring in the colonies of Alderley Park strain 1 rats and strain 1 mice has been studied in a series of experiments in which animals were subjected to various dietary regimes for the majority of their lifespan. A twenty percent reduction of food intake produced a marked reduction in total tumor incidence; liver tumors in mice, and pituitary and mammary tumors of rats were most affected; brain tumors in rats and thymic tumors in mice were not affected by dietary manipulations indicating that they have a different aetiology. Commercial diets (Oxoid and Purina) produced a different pattern of mortality when fed ad libitum; this appeared to be related to calorific values of the diets not food intake. Calorific values, rather than protein levels, appeared more important in tumor development in the rat. A lifespan food restriction in mice eliminated the development of some tumors, and retarded the onset of all types except thymic tumors. When food intake was restricted only for the first four months of life it did not prevent the animals from reaching their usual maximum body weight. Food restriction did not eliminate the sensitivity of mice to a specific carcinogen.