The Effect of Exercise on Metabolism Following the Ingestion of Water, Glucose and Fructose, as Shown by the Course of the Respiratory Quotient

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Abstract
The respiratory quotient as affected by exercise taken immediately after the ingestion of 500 cc. water, 50 gm. glucose, 50 gm. fructose, and a mixture of 25 gm. each of these two sugars dissolved in 500 cc. water at 37°C. has been studied on two subjects. The exercise consisted of performing 550 kilogrammeters of work per minute for two consecutive 15-minute periods on a Prony brake bicycle ergometer. In the control experiments with water, the respiratory quotient rose to approximately 0.90 during exercise, an increase of 0.10 above the base line. The quotient of one subject was slightly higher during the second 15-minute period, whereas that of the other remained the same. The increase of the respiratory quotient during exercise was practically the same when the sugars were ingested as when water alone was taken immediately before the exercise. The rise in the respiratory quotient during exercise in the experiments with water and the sugars shows that there was an increase in the relative and absolute amount of carbohydrate oxidized. Since the same rise in the quotient was obtained in the experiments with the various sugars as in the control experiments with water, it is concluded that the percentage of carbohydrate oxidized was not increased by the ingestion of the sugars immediately before exercise. Glucose and fructose were equally ineffective in raising the percentage of carbohydrate oxidized during exercise. Practically the same amount of carbohydrate was oxidized during exercise in the control and various sugar experiments. In all the experiments there was more carbohydrate oxidized in the second than in the first exercise period. During the first recovery period in the control experiments with water the respiratory quotient remained at practically the same level as during exercise, indicating that the increase in carbohydrate metabolism induced by exercise persisted some few minutes afterward. In the experiments with the sugars there was a rise in the quotient during the first recovery period above the level reached during exercise. The greatest rise occurred in the experiments with a mixture of the sugars, the least in those with glucose. This may be explained in part as a superposition of the metabolism of the sugars on the normal metabolism of recovery. The data have been interpreted as suggestive of the conversion of a portion of the glucose into fat and of an acceleration of this process by exercise. Exercise accelerated the metabolism of glucose whereas it had no effect on that of fructose. Inasmuch as the ingested glucose did not increase the total carbohydrate oxidation during exercise, it must have had a greater sparing effect than fructose on the body stores of carbohydrate.