Protein requirements in tropical countries: nitrogen losses in sweat and their relation to nitrogen balance.

I. An experiment was undertaken to determine whether high rates of sweating in a tropical climate affect protein requirements by increasing the total nitrogen losses from the body. 2. Six fully acclimatized volunteers were given a diet supplying 5 0 g protein (= 8 g N) daily. They performed strenuous physical work of a normal nature for an average of 64 h a day for two 5-day periods. During control periods the subjects took minimal exercise and lived in a cool environment. N balance was measured throughout. 3. Rates of sweating were measured by weighing. Whole body sweat was collected and the concentrations were measured of nitrogen, sodium and potassium. During 64 h work approximately 3 1. of sweat were lost, containing on average 0.49 g N, 64 m-equiv. Na and 22 m-equiv. K. 4. TheNconcentration in sweat was o*zomg/g, which is lower than that found by most other workers. It is suggested that acclimatization is an important factor in reducing N loss by sweating. 5. There was a marked decrease in urinary Na excretion during sweating, which compensated fully for the loss of Na in sweat. Renal compensation for loss of K was less efficient. 6. Because the total N loss in sweat was small, it was not possible to establish with certainty whether it was compensated for by a reduced renal excretion of N. However, after the initial period the subjects were in N balance in spite of the relatively low protein intake. 7. It is concluded that there is no evidence to suggest that heavy sweating under natural conditions in a tropical climate causes a significant increase in protein requirements. Recently suggestions have been put forward that protein requirements may be higher in tropical than in temperate countries because of the loss of nitrogen in sweat. (1963) have proposed that protein allowances should be increased by 13-14%, whilst Mitchell & Edman (1962) state that increases of the order of 20-30% are necessary. Consolazio, Nelson et al. (1963) based their proposals on studies carried out in an environmental chamber at 85' and I O O O F in Denver, Colorado. During 79 h sweating at 85 O F eight young men lost on average 1815 g of sweat containing 1.418 g N. When three young men spent 2 1 h at I O O O F , it was estimated that they would each lose over 4 g …