The role of palatability in the food intake response of rats fed high-protein diets.

Male albino rats, trained to eat over a 3-h period, reduced their food intake from 0.38 +/- 0.04 g of a low-protein diet to 0.14 +/- 0.03 g of a high-protein diet, within 1 min following diet presentation. Since this occurred before the metabolic effects of a high-protein diet should be seen, we suggest that, although neophobia could play a role, poor initial palatability may be a significant factor in this early depression in food intake. To differentiate initial palatability from responses to metabolic feedback, we designed a feeding paradigm using positive or negative taste cues and a 6-h feeding period. Pre-treatment with a 6% casein diet containing 0.15% quinine HCl resulted in near equal consumption of a 75% casein and a 6% casein unadulterated diet during the first 30 min after introduction of the diets. Later, the rate of consumption of the high-protein diet was lower than of the lower-protein diet, likely the result of post-absorptive factors. We suggest that prevention of the early reduction in food intake due to initial palatability may facilitate study of post-absorptive response(s) to high-protein diets.