Effect of Dietary Fats and Carbohydrates on Digestibility of Nitrogen and Energy Supply, and on Growth, Body Composition and Serum Cholesterol of Rats

Abstract

Groups of male and female rats were fed stock or purified low-fat diets and similar diets with corn oil, hydrogenated vegetable oil, or lard added. Records of weight gains and food intakes were kept until the animals were killed when either 200 or 400 days old. Of the groups of male animals, those fed the low-fat stock diet and the low-fat purified diet with cornstarch as the carbohydrate had the lowest final body weights and those fed 15% corn oil, with sucrose as the carbohydrate had the highest final body weight. Weight gains were correlated with apparent digestible energy intake (r = 0.91) but not necessarily with fat intake; the average final weight of the group of animals receiving the low-fat diet with sucrose as the carbohydrate was not significantly higher than the weights of the animals which received 15% hydrogenated vegetable oil or lard. The addition of any of the fats improved digestibility of the energy supply of the stock diet but had no consistent effect on digestibility of the purified diets. Digestibility of nitrogen supply and nitrogen retention expressed as per cent of nitrogen intake did not appear to be related to kind or amount of fat in the diet. The animals receiving the purified diets containing sucrose and either three or 15% corn oil had significantly more body fat than those receiving corresponding diets containing cornstarch, or the stock diets. Of the male animals 400 days old, those which received 15% corn oil and sucrose had the highest body fat, and had the highest level of serum cholesterol, but there was no correlation (r = -0.27) between per cent body fat and serum cholesterol for animals of this group. The per cent of the digestible calorie intake stored as fat was significantly higher for the groups of animals fed the diets containing sucrose and three or 15% corn oil than for animals receiving comparable diets containing cornstarch, or the stock diets. When animals with the same calorie intake were compared, regardless of kind or level of fat, those which received sucrose stored a higher per cent of their caloric intake as fat than those which received cornstarch.