Food Preference and Protein Intake of Normal and Diabetic Rats Fed Diets Varying in Protein Quality and Quantity

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Abstract
An investigation was made of differences in food preference and protein intake between normal and chronically alloxan-diabetic rats allowed to select from two diets that varied in protein quality and quantity. Diabetic rats, unlike normal rats, had a decreased preference for a basal (6% casein + 0.3% met) diet and an increased preference for a histidine imbalanced (basal plus 6% amino acid mix minus His) diet. However, diabetic rats, like normal rats, predominantly selected a 10% casein (plus 0.3% met) diet when offered a choice of that diet and a protein free or 50% casein diet. It appeared that diabetic rats were unresponsive to the difference in protein quality but aware of the difference in protein quantity of the diets presented for selections. Ingestion of the histidine imbalanced diet by the diabetic rats caused a 20 and 37% decrease in the concentration of plasma and brain histidine, respectively; however, ingestion of the same diet by normal rats caused a 48 and 43% decrease in the limiting amino acid, respectively. The smaller decrease in the plasma histidine level in the diabetic rats appeared to be due to redistribution of amino acids within the body. There was a shift of 14C-labeled histidine ingested from muscle and heart to some other organs and expired CO2 due to diabetes. Regardless of the type of diets presented for choice, diabetic rats had higher intakes of protein as well as energy per unit body weight than normal rats. The higher intakes of protein and energy were associated with lower ratios of plasma Trp/NAA and Tyr/Phe, a lower concentration of brain tyrosine and a higher (but not significantly higher) concentration of brain tryptophan.