The Timing of Protein Feeding and Dietary Protein Levels Affect Taste Preference, Serum Zinc Concentration and Glossal Epithelial Morphology in Growing Rats

Abstract

Objective: The present study investigated the effect of timing of protein feeding on taste preference, serum zinc concentration and morphological changes of tongue epithelia.Methods: Weanling rats were fed one of three diets: protein-free and 2.5 or 8% purified egg protein (PEP) diets for 14 days (first feeding period). Rats in each group were further subdivided into three dietary treatments, totaling nine groups and fed one of the same three diets for 14 days (second feeding period). Preference tests between 3 or 6 mmol/L NaCl vs. deionized water were conducted in both feeding periods. At the end of each period, blood and tongue were collected for the measurement of serum zinc concentrations and morphological observations.Results: The rats fed the protein-free diet in the first feeding period did not discriminate 3 mmol/L NaCl from deionized water in both feeding periods, even though adequate protein was administered in the second feeding period. The rats fed the 2.5 or 8% PEP diet in the first feeding period discriminated 3 mmol/L NaCl from deionized water regardless of the protein levels in the diet during the second feeding period. Serum zinc concentration was proportionate to protein content in the diet at the end of each feeding period (p<0.0001), and low serum zinc concentration was restored by protein feeding. Abnormal changes of tongue epithelia were observed only in the rats fed the protein-free diet throughout the two feeding periods.Conclusions: The results suggest that protein nutrition immediately after weaning is important to maintain normal taste function.