Some Metabolic Effects of Prolonged Feeding of Starch, Sucrose, Fructose and Carbohydrate-Free Diet in the Rat

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Abstract
Male rats of the ASL Wistar strain were fed from weaning on starch, fructose or carbohydrate-free diets for 4 and 12 weeks. In addition, further groups were fed for 24 weeks on starch, sucrose or carbohydrate-free diets. Livers were examined for gross composition, glucose-6-phosphatase activity and in vitro lipogenesis and glucose oxidation. Intestinal sucrase was also measured. Dietary fructose and the carbohydrate-free diet induced an enlargement of the livers after 12 weeks feeding, when expressed per 100 g body weight, and at the same time, an increased fat content. Fructose caused an increase in liver glucose-6-ρhosphatase after 4 weeks, which persisted after 12 weeks, and a similar increase was observed after 24 weeks feeding on sucrose. Fructose produced an increase in intestinal sucrase after 4 weeks, but this did not persist and there was no increase evident after 12 weeks feeding, nor after 24 weeks feeding on sucrose. Fructose markedly depressed the in vitro lipogenesis and glucose oxidation in liver slices. This was evident after 4 weeks feeding and also after 12 weeks when the effect of age showed as a fall in both these parameters in the control group of animals. The carbohydrate-free diet caused an increase in liver glucose-6-phosρhatase after 4 weeks, a smaller increase after 12 weeks, and there was no increase apparent when feeding was continued for 24 weeks. Apparently due to the absence of substrate, the intestinal sucrase activity fell to less than half after 4 weeks and to negligible levels after 12 and 24 weeks on carbohydrate-free diet. In vitro liver lipogenesis and glucose oxidation were depressed after 4 and 12 weeks in a similar way to the fructose diet. On both these diets the rise in liver glucose-6-phosphatase appeared to parallel the fall in liver lipogenesis and glucose oxidation.