Exercise training modifies nutrient self-selection in rats

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Few studies have examined the effects of exercise training on macronutrient self-selection in rats. It has been observed that trained rats decreased carbohydrate and increased fat and protein intakes. In the present experiment, total energy intake and macronutrient self-selection were examined in adult male rats placed on a self-selection regimen and submitted to 2 h of treadmill exercise daily for 20 days at the beginning of the nocturnal period. Two control groups of rats were examined during the same time: a sedentary group that was food and water deprived during the same 2 h while trained rats were exercising, and a control group that was examined only for body weight gain and 24-h food intake. Food intakes of sedentary and trained rats were continuously recorded. At the end of the experiment, body weight of trained rats was lower than that of sedentary and control rats. The 24-h cumulative intake of trained rats was significantly reduced; this reduction was due to a decrease in fat intake, whereas carbohydrate intake was increased. In sedentary rats, 24-h intake was not modified but fat intake was significantly increased from the beginning to the end of the experiment. During the first 6 h of the night, protein and fat intakes of trained rats were reduced, and carbohydrate ingestion remained the same. Daytime food intake represented only 8.7% of the 24-h intake. Exercise training significantly increased this intake. It is noteworthy that during the middle part of the day (3–9 h) trained rats significantly enhanced 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 increased carbohydrate intake, early in the light period preceding exercise, might improve exercise endurance, whereas sedentary rats anticipate an obligatory induced fast by increasing fat intake.