Dietary Protein and Physical Fitness in Temperate and Hot Environments

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Abstract
The effect of variation in the level of dietary protein upon the physical fitness and metabolism of three subjects was studied under both temperate and tropical conditions while reclining, standing and marching. The urinary nitrogen excretion in grams per day averaged 18.5 during the high protein period, 9.5 during the low protein period and 12.9 and 13.5 during the normal periods before and after the experiment, respectively. There were minor changes in body weight with a maximum during the high protein period. The plasma protein level showed no significant changes. Physical fitness under temperate conditions showed no changes attributable to dietary protein level. Performance of work in both hot, dry and hot, moist environments showed no changes attributable to dietary protein level. In both cases, however, improvements due to training and acclimatization were observed. Metabolism while reclining and while standing was not significantly different in the high and low protein periods. Metabolism while marching was slightly lower in the low protein period. However, as judged by actual performance in the heat this was a physiologically insignificant change. It is concluded that even though protein does have a high specific dynamic action, the theoretical objections heretofore raised against a high protein diet in hot environments are unjustified under the conditions of our observations. Protein intake may vary widely from 75 to 150 gm. daily without effect upon performance of intermittent work in the heat.

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