No Change in 24-Hour Hydration Status Following a Moderate Increase in Fluid Consumption.

PURPOSE: To investigate changes in 24-hour hydration status when increasing fluid intake. METHODS: Thirty-five healthy males (age 23.8 ± 4.7 years; mass 74.0 ± 9.4 kg) were divided into 4 treatment groups for 2 weeks of testing. Volumes of 24-hour fluid ingestion (including water from food) for weeks 1 and 2 was 35 and 40 ml/kg body mass, respectively. Each treatment group was given the same proportion of beverages in each week of testing: water only (n = 10), water + caloric cola (n = 7), water + noncaloric cola (n = 10), or water + caloric cola + noncaloric cola + orange juice (n = 8). Serum osmolality (Sosm), total body water (TBW) via bioelectrical impedance, 24-hour urine osmolality (Uosm), and volume (Uvol) were analyzed at the end of each 24-hour intervention. RESULTS: Independent of treatment, total beverage consumption increased 22% from week 1 to 2 (1685 ± 320 to 2054 ± 363 ml; p < 0.001). Independent of beverage assignment, the increase in fluid consumption between weeks 1 and 2 did not change TBW (43.4 ± 5.2 vs 43.0 ± 4.8 kg), Sosm (292 ± 5 vs 292 ± 5 mOsm/kg), 24-hour Uosm (600 ± 224 vs 571 ± 212 mOsm/kg), or 24-hour Uvol (1569 ± 607 vs 1580 ± 554 ml; all p > 0.05). CONCLUSIONS: Regardless of fluid volume or beverage type consumed, measures of 24-hour hydration status did not differ, suggesting that standard measures of hydration status are not sensitive enough to detect a 22% increase in beverage consumption.

Hydration Status over 24-H Is Not Affected by Ingested Beverage Composition.

OBJECTIVE: To investigate the 24-h hydration status of healthy, free-living, adult males when given various combinations of different beverage types. METHODS: Thirty-four healthy adult males participated in a randomized, repeated-measures design in which they consumed: water only (treatment A), water+cola (treatment B), water+diet cola (treatment C), or water+cola+diet cola+orange juice (treatment D) over a sedentary 24-h period across four weeks of testing. Volumes of fluid were split evenly between beverages within each treatment, and when accounting for food moisture content and metabolic water production, total fluid intake from all sources was equal to 35 ± 1 ml/kg body mass. Urine was collected over the 24-h intervention period and analyzed for osmolality (Uosm), volume (Uvol) and specific gravity (USG). Serum osmolality (Sosm) and total body water (TBW) via bioelectrical impedance were measured after the 24-h intervention. RESULTS: 24-h hydration status was not different between treatments A, B, C, and D when assessed via Uosm (590 ± 179; 616 ± 242; 559 ± 196; 633 ± 222 mOsm/kg, respectively) and Uvol (1549 ± 594; 1443 ± 576; 1690 ± 668; 1440 ± 566 ml) (all p > 0.05). A -difference in 24-h USG was observed between treatments A vs. D (1.016 ± 0.005 vs. 1.018 ± 0.007; p = 0.049). There were no differences between treatments at the end of the 24-h with regard to Sosm (291 ± 4; 293 ± 5; 292 ± 5; 293 ± 5 mOsm/kg, respectively) and TBW (43.9 ± 5.9; 43.8 ± 6.0; 43.7 ± 6.1; 43.8 ± 6.0 kg) (all p > 0.05). CONCLUSIONS: Regardless of the beverage combination consumed, there were no differences in providing adequate hydration over a 24-h period in free-living, healthy adult males. This confirms that beverages of varying composition are equally effective in hydrating the body.