Dietary carbohydrates: effects on self-selection, plasma glucose and insulin, and brain indoleaminergic systems in rat

The aim of the study was to investigate the effect of different dietary carbohydrates such as corn starch, sucrose, fructose and glucose on carbohydrate and protein self-selection and on arterial and venous concentrations of glucose and insulin, and brain indoleamines in rats. Fructose and sucrose feeding induced the lowest food intakes which were due respectively to a lower carbohydrate and protein selection. The present data showed that feeding with dietary glucose as the main carbohydrate source gave the highest glycemic response, the lowest one being found with fructose and corn starch, and an intermediate one with sucrose feeding. The insulin response to the dietary carbohydrates followed a somewhat different pattern with the highest insulin secretion observed after fructose feeding whereas highly variable and inconsistent results were obtained following corn starch, sucrose and glucose feeding. Feeding chemically different sugars was also characterized by decreased serotonin synthesis in the raphe nuclei, brainstem and thalamus, and increased 5-HT synthesis in the hypothalamus of rats fed fructose when compared to glucose fed animals. The present results highlight the importance of considering the nature of dietary carbohydrates in the regulation of feeding.