THE TIMING OF PROTEIN FEEDING AND DIETARY-PROTEIN LEVELS AFFECT TASTEPREFERENCE, SERUM ZINC CONCENTRATION AND GLOSSAL EPITHELIAL MORPHOLOGY IN GROWING RATS

Objective: The present study investigated the effect of timing of prot ein feeding on taste preference, serum zinc concentration and morpholo gical 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 fur ther subdivided into there dietary treatments, totaling nine groups an d 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 an d tongue were collected for the measurement of serum zinc concentratio ns and morphological observations. Results: The rats fed the protein-f ree diet in the first feeding period did not discriminate 3 mmol/L NaC l from deionized water in both feeding periods, even though adequate p rotein 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 di et during the second feeding period. Serum zinc concentration was prop ortionate to protein content in the diet at the end of each feeding pe riod (p<0.0001), and low serum zinc concentration was restored by prot ein feeding. Abnormal changes of tongue epithelia were observed only i n the rats fed the protein-free diet throughout the two feeding period s. Conclusions: The results suggest that protein nutrition immediately after weaning is important to maintain normal taste function.