COMPARISON OF GROUND-BASED AND SPACE-FLIGHT ENERGY-EXPENDITURE AND WATER TURNOVER IN MIDDLE-AGED HEALTHY MALE US ASTRONAUTS

Energy requirements during space flight are poorly defined because the y depend on metabolic-balance studies, food disappearance, and dietary records. Water turnover has been estimated by balance methods only. T he purpose of this study was to determine energy requirements and wate r turnover for short-term space flights (8-14 d). Subjects were 13 mal e astronauts aged 36-51 y with normal body mass indexes (BMIs). Total energy expenditure (TEE) was determined during both a ground-based per iod and space flight and compared with the World Health Organization ( WHO) calculations of energy requirements and dietary intake. TEE was n ot different for the ground-based and the space-flight periods (12.40 +/- 2.83 and 11.70 +/- 1.89 MJ/d, respectively), and the WHO calculati on using the moderate activity correction was a good predictor of TEE during space flight. During the ground-based period, energy intake and TEE did not differ, but during space flight energy intake was signifi cantly lower than TEE; body weight was also less at landing than befor e flight, Water turnover was lower during space flight than during the ground-based period (2.7 +/- 0.6 compared with 3.8 +/- 0.5 L/d), prob ably because of lower fluid intakes and perspiration loss during fligh t. This study confirmed that the WHO calculation can be used for male crew members' energy requirements during short space flights.