The Influence of Varying Levels of Dietary Protein, Carbohydrate and Fats in the Nutrition of the Rat

Abstract

The effects of varying levels of dietary protein, carbohydrate and fats on the nutrition of the rat over a 57-week feeding period were studied. After the rats had received the test diets for 4 weeks, those fed diets containing 50% of their calories as casein had superior rates of gain and utilization of crude calories as compared with rats fed diets containing either 20 or 80% of their calories as casein. Lard or corn oil substituted at the expense of sucrose increased the caloric efficiency of rats fed the diets containing 50 or 80% of their calories as casein. No apparent differences in average serum cholesterol, average total serum polyunsaturated fatty acids, and average liver cholesterol were noted between the dietary groups through the initial 22 weeks of this study. After 57 weeks, high levels of dietary casein tended to increase serum cholesterol and to decrease liver cholesterol. Substitution of lard at the expense of sucrose tended to increase serum cholesterol at the low and high dietary casein levels, and to increase total liver cholesterol at all dietary casein levels. Substitution of corn oil at the expense of sucrose tended to decrease serum cholesterol at the intermediate and high dietary casein levels and to increase liver cholesterol at all dietary casein levels. The highest liver cholesterol values were obtained in the groups fed corn oil at the lowest dietary casein level. The average total polyunsaturated fatty acids of the serum was increased in the groups fed the high level of casein plus either lard or corn oil. No evidence of abnormal fat deposits was observed in any of the hearts and aortas from these animals.