VALIDATION OF DOUBLY LABELED WATER FOR MEASUREMENT OF CALORIC EXPENDITURE IN COLLEGIATE SWIMMERS

To validate doubly labeled water (DLW) in aquatic athletes, energy expenditures (EE) were determined by energy intake/balance (IB) and DLW in free-living collegiate swimmers [n = 8, age 20.1 +/- 1.7 (SD) yr, height 186 +/- 11 cm, weight 74.1 +/- 9.3 kg] over 9 days. EE(IB) was determined from caloric analysis of duplicate foods to those consumed by subjects and corrected for changes in body composition across the study. For EE(DLW), subjects were given (H2O)-H-2 and (H2O)-O-18 on day 0 and (H2O)-H-2 on day 10. Day 0 and 10 body compositions were measured by use of H-2 dilution space, and elimination rates over days 1-10 were determined for H-2 and O-18. EE(DLW) was calculated from CO2 respiratory quotient by use of a food quotient. Fat mass increased (P < 0.01) over the study period. Mean uncorrected energy intake was 3,895 +/- 621 kcal/day. When all eight subjects were compared, EE(IB) and EE(DLW) were 3,492 +/- 876 and 3,466 +/- 992 kcal/day, respectively. Data from one subject compared poorly despite repeat isotopic analyses. In the remaining seven subjects, EE(IB) and EE(DLW) were 3,444 +/- 925 and 3,556 +/- 1,025 kcal/day, respectively. These data indicate that DLW is a good indicator of EE in groups of swimmers and that energy requirements of swimmers are similar to other athletic groups.