Rehydration after Exercise with Common Beverages and Water

Abstract

This study assessed the effectiveness of two common rehydration beverages (a caffeinated diet cola (DC) and a 6% carbohydrate-electrolyte (CE) solution) compared with water (W) for whole body rehydration, gastric emptying and blood volume (BV) restoration during a 2 h rehydration period following exercise-induced dehydration. Subjects (mean V̇O 2 max = 4.2±0.6 1 · min -1 min -1 ; n = 19) exercised at 60-80% V̇O 2 max in the heat (32 °C; 40% rh) until ˜ 2.5% (1.95±0.12 kg) of their body weight (BW) was lost. After exercise, the subjects sat for 2 h in a thermoneutral environment (21 °C; 60% rh) and drank a volume of DC, W and CE equal to the fluid lost. Fluids were consumed in two boluses averaging 1,046±198 and 912±186 ml at 0 and 45 min of the 2 h rehydration period, respectively. At the end of the rehydration period, no fluid remained in the stomach during any of the trials as indicated by epigastric impedance. However, in all the trials the subjects were somewhat hypohydrated (range 0.6-0.9 kg BW below euhydrated BW; p < 0.05) after the 2 h rehydration period since additional water and BW were lost as a result of urine formation, respiration, sweat and metabolism. The percentage of body weight loss that was regained (used as an index of % rehydration) during DC (54±5%) was significantly lower than that of W and CE (64±5% and 69±5%, respectively; p < 0.05; n = 10). Additionally, the percent rehydration during W was significantly lower than that of CE (65±3% vs 73±3%, respectively; p < 0.05; n = 19). The lower whole body rehydration observed with DC compared with CE and W compared with CE was due mostly to greater urine formation (710±102 vs. 483±91 ml, p < 0.05, n = 10; and 505±61 vs. 339±61 ml, p < 0.05, n = 19, respectively). The decline in blood volume as a result of exercise was not restored during the rehydration period by ingesting DC and W, whereas blood volume was fully restored with CE ingestion (p < 0.05). The ingestion of DC is less effective than water for whole body rehydration, whereas ingestion of CE is somewhat more effective than both W and DC.