THE EFFECTS OF A HIGH-CARBOHYDRATE DIET ON POSTPRANDIAL ENERGY-EXPENDITURE DURING EXERCISE IN RATS

Whether or not a high intake of carbohydrate increases postprandial en ergy expenditure during exercise was studied in rats. The rats were me al-fed regularly twice a day (0800-0900 hours and 1800-1900 hours) on either a high carbohydrate (CHO) (carbohydrate/fat/protein = 70/5/25, % of energy) or high fat (FAT) (35/40/25) diet for 12 days. On the fin al day of the experiment, all of the rats in each dietary group were f ed an evening meal containing equal amounts of energy (420 kJ.kg-1 bod y mass). After the meal, they were divided into three subgroups: pre-e xercise control (PC), exercise (EX), and resting control (RC). The PC- CHO and PC-FAT groups were sacrificed at 2030 hours. The EX-CHO and EX -FAT groups were given a period of 3-h swimming, and then sacrificed a t 2330 hours. The RC-CHO and RC-FAT groups rested after the meal and w ere sacrificed at 2330 hours. Total energy expenditure during the peri od 1.5 h from the commencement of exercise was higher in EX-CHO than i n EX-FAT. The respiratory exchange ratio was also higher in EX-CHO tha n in EX-FAT, suggesting enhanced carbohydrate oxidation in the former. Compared with both PC-FAT and RC-FAT, the liver glycogen content of E X-FAT rats was significantly decreased by exercise. On the other hand, the liver glycogen content of both EX-CHO and RC-CHO was higher than that of PC-CHO rats. The glycogen content of soleus muscle of EX-FAT w as slightly decreased during exercise, however, that of EX-CHO increas ed significantly. Thus postprandial energy expenditure during exercise was higher in the rats fed the CHO diet than in those fed the FAT die t, which could have been related to the increase of both liver and mus cle glycogen storage during exercise in the former.