Interaction of dietary protein with cellulose in the adaptation of caloric dilution by weaning rats.

The adaptive response of food intake to increasing levels of dietary cellulose was studied in weanling rats fed limiting amounts of dietary protein of different qualities. At low levels of dietary cellulose, the food intake depends on protein quality. As the cellulose levels were increased, the diet and gross energy digestibilities diminished, yielding diets with lower digestible energy contents. The rats fed the higher quality protein were able to compensate for this caloric dilution, increasing their food consumption enough to keep constant their digestible energy intake. The animals fed a lower quality protein, however, were unable to make this adaptive increase in food intake. As a result, although gross food intake remained stable, cellulose constituted an increasing proportion of it and the digestible energy consumption of these animals diminished. Water consumption in this trial appears to reflect the animal's digestible energy intake rather than cellulose consumption. The above observations may be considered as an indication that a smooth regulation of the energy intake occurs only with a complete or non-deficient diet and that deficient, abnormal or unusual diets upset this process. In the present experimental situation, when dietary protein is inadequate, the animal can no longer make appropriate compensatory increases in its food consumption to keep its digestible energy intake constant.