Effect of Meal Frequency and Diet Composition on Glucose Tolerance in the Rat

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Abstract
It has been reported that rats fed one 2-hour high carbohydrate meal per day remove a load of glucose from the circulation more rapidly than do ad libitum-fed rats. Conversely, humans subjected to decreased meal frequency exhibit an impaired glucose tolerance. Composition of diet has been reported to affect glucose tolerance. In this study rats were fed high carbohydrate diets (glucose or sucrose) or high fat diets to determine whether diet composition could modify the effect of meal frequency on glucose tolerance. One hundred eighty-two glucose tolerance tests were performed. Both oral and intraperitoneal glucose tolerance tests indicated that meal-fed rats cleared glucose from the circulation faster than did nibbling rats. Addition of fat to the high carbohydrate diet impaired glucose tolerance. Replacement of dietary glucose with sucrose also impaired glucose tolerance in meal-fed rats. Changes in in vitro conversion of glucose to fatty acids were consistent with changes observed in glucose tolerance. Adipose tissue from meal-fed rats exhibited a greater capacity to convert glucose to fatty acids than did adipose tissue from nibbling rats. Addition of fat to the diet markedly depressed fatty acid synthesis in adipose tissue and liver. Replacement of dietary glucose with sucrose also decreased adipose tissue conversion of glucose to fatty acids. These results suggest that the differential effect of meal frequency on glucose tolerance in rats and humans cannot be attributed entirely to differences in diet composition.