Muscular Efficiency on High Carbohydrate and High Fat Diets

Abstract

Forty-seven experiments on the muscular efficiency of a single subject while riding the bicycle ergometer are reported. Twelve of the experiments were made while the subject was subsisting on a normal ad libitum diet. The last seven of these served as a basal series with which to compare subsequent experiments while the subject was subsisting on high carbohydrate and high fat diets. The high carbohydrate diet contained 2400 Cal. daily of which 80% came from carbohydrate and approximately 12 and 8% respectively from fat and protein. The high fat diet contained 2800 Cal. of which 80% came from fat and approximately 12 and 8% respectively from carbohydrate and protein. Two series of experiments were run on each of these diets, nearly equally distributed between post-absorptive experiments and experiments taken 4 to 5 hours after a meal rich in carbohydrate or fat. The work was of the same duration (eight minutes) followed by a recovery period, in the same metabolism period, of 17 to 25 minutes on each diet, but differed as regards rate in the first and second series on each diet. Urine was collected in two periods, the first including the pre-work resting period and the second the work and recovery as well as a second post-work resting period. The calculation of efficiency included the protein metabolism in all experiments. The extra metabolism due to work is found by subtracting from the total metabolism for the work and recovery period, the pre-work resting metabolism calculated each time to the same length of period. The average net efficiency on the normal diet at the rate of 1.4 Cal. of work per minute was 22.1%; on high carbohydrate at the same rate, 22.7%; on high fat at the same rate 21.5%. At the lower rate of 1.1 Cal. of work per minute the average net efficiency on the same high carbohydrate diet was 23.4%, and on the high fat 22.6%. On the high carbohydrate diet there was no progressive change in the efficiency, but on high fat the efficiency progressively declined from the 3rd or 4th day of the diet to the 7th in one series and still more to the 11th day in the other. The average difference in efficiency between high carbohydrate and high fat first series, calculated to pure carbohydrate and pure fat combustion, was 11 or 12% (relative), agreeing with previous results found by Frentzel and Reach (1901) and by Krogh and Lindhard (1920). A difference in the diminution of nitrogen excretion from pre-work to work and recovery periods was noted on the high carbohydrate as compared with the high fat diet. This difference is due to the greater sparing effect of increased carbohydrate combustion. Relative to the increase in carbohydrate calories, the decreased protein metabolism was the same on both diets, but since it is total metabolism which affects efficiency, the effect of the greater sparing of protein (on high carbohydrate) depends upon whether the protein calories replace non-protein under the conditions of these experiments. Direct calorimetry would be required to settle this question. The effect of the specific dynamic action of higher protein and fat metabolism would require blood analyses which were not attempted in these experiments.