Dietary practices of early life and spontaneous tumors of the rat.

A complete life history was obtained of the dietary practices, growth responses, and diseases of outbred male Charles River COBS rats permitted to select their own diets. Simple correlation analyses proved inadequate for detecting an association between any single factor at any age and tumor development. A multifactorial model showed that animals that developed tumors could be distinguished from those that did not, solely on the basis of age- or weight-specific information prior to maturity. The combination of variables that maximize the probability of a neoplasm is: 1. a high absolute protein intake shortly after weaning, 2. a high degree of efficiency in converting consumed food into body mass at the time the individual enters puberty, 3. a high level of protein intake relative to body weight during the early adult period and concomitantly, 4. a high level of food intake, and 5. a rapid growth rate during early postnatal life so that comparatively less time is required to attain a specified body weight than a subsequent weight increment. The opposite set of conditions reduces the probability of neoplasm occurrence, which is even further minimized if the proportion of protein in the diet in early postweaning life and the absolute intake of protein during the early adult period are relatively high. Differences in temporal-specific dietary practices and growth responses accounted for differences in the tissue origin of the tumors.