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

Abstract

1. 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 50 g protein (= 8 g N) daily. They performed strenuous physical work of a normal nature for an average of 6½ 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 6½ h work approximately 3 l. of sweat were lost, containing on average 0·49 g N, 64 m-equiv. Na and 22 m-equiv. K.4. The N concentration in sweat was 0·20 mg/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.