EXERCISE TRAINING MODIFIES NUTRIENT SELF-SELECTION IN RATS

Few studies have examined the effects of exercise training on macronut rient self-selection in rats. It has been observed that trained rats d ecreased carbohydrate and increased fat and protein intakes. In the pr esent experiment, total energy intake and macronutrient self-selection were examined in adult male rats placed on a self-selection regimen a nd submitted to 2 h of treadmill exercise daily for 20 days at the beg inning of the nocturnal period. Two control groups of rats were examin ed during the same time: a sedentary group that was food and water dep rived during the same 2 h while trained rats were exercising, and a co ntrol group that was examined only for body weight gain and 24-h food intake. Food intakes of sedentary and trained rats were continuously r ecorded. At the end of the experiment, body weight of trained rats was lower than that of sedentary and control rats. The 24-h cumulative in take of trained rats was significantly reduced; this reduction was due to a decrease in fat intake, whereas carbohydrate intake was increase d. In sedentary rats, 24-h intake was not modified but fat intake was significantly increased from the beginning to the end of the experimen t. During the first 6 h of the night, protein and fat intakes of train ed rats were reduced, and carbohydrate ingestion remained the same. Da ytime food intake represented only 8.7% of the 24-h intake. Exercise t raining significantly increased this intake. It is noteworthy that dur ing the middle part of the day (3-9 h) trained rats significantly enha nced protein and carbohydrate ingestion. In sedentary rats during the 3 h preceding fasting, fat intake increased. The present results could be ascribed to an anticipatory phenomenon. In trained rats, an increa sed carbohydrate intake, early in the light period preceding exercise, might improve exercise endurance, whereas sedentary rats anticipate a n obligatory induced fast by increasing fat intake.