Dietary Protein and Utilization of Vitamin A

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Abstract
The effect of protein quantity and quality on vitamin A utilization was studied by administering a large dose of vitamin A to rats at the start of the test and measuring the vitamin A remaining in the liver and kidneys after the test diets were fed for three weeks. Highest vitamin A content was observed in the livers of rats fed a protein-free diet. With an increase in the dietary protein there was a progressive decrease in the amount of vitamin A in the liver and an increase in the amount of vitamin A in the kidneys. A linear relationship was observed between weight gain and vitamin A utilization. The utilization of vitamin A was also affected by protein quality. In rats ingesting an 18% casein diet, less vitamin A was observed in the liver and more in the kidneys than in slower-growing animals fed 18% of either gluten or zein. Amino acid supplementation of gluten and zein resulted in an improved growth rate, increased depletion of hepatic vitamin A and greater total utilization of the vitamin. The efficiency of vitamin A utilization, calculated after correction for the maintenance requirement, was decreased by inferior protein quality, but was not affected by the level of dietary protein.