Tumor Incidence Patterns and Nutrition in the Rat

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Abstract
Levels of caloric and of protein intake were demonstrated to have a modifying influence on tumor incidence patterns in the male rat. The 5 uniform life-long dietary regimens used differed only in allotments and intakes of protein (casein), carbohydrate (sucrose) or of total calories. Age-specific rate tables and tumor incidence ratios aided in assessment of the nutritional effects. Total tumor risk was directly and exponentially related to caloric intake, but time differences for development of each of the incidence patterns were related inversely to caloric intake. Among all the groups tumor incidences formed an exponential continuum when related to growth rate in early life and mature body weight. Within each dietary group, rats of heavier weight had greater tumor risk than lighter rats. Occurrence, the proportional incidence and the malignancy of certain tumors correlated with the level of protein intake. Malignant lymphomas were predominant in rats with high protein intake, whereas fibromas and fibrosarcomas predominated in rats with low protein intake. Tumor incidence patterns differed quantitatively, qualitatively or both. Thus, in 2 groups with identical caloric intake, risk for all tumor types was similar but the group with higher protein had a greater risk for malignancy. Rate patterns for benign tumors, but not for malignant tumors, were dependent upon the mortality rate patterns of their respective populations. Lowest incidence, greatest delay in time of occurrence, absence of malignant epithelial tumors and greatest life expectancy, were observed when intakes of protein, carbohydrate and total calories were low.

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