Fluid replacement after dehydration: Influence of beverage carbonation and carbohydrate content

This investigation evaluated the effects of beverage carbonation and carbohydrate (CHO) content on fluid replacement following exercise/thermal dehydration. On four occasions separated by at least 7 days, eight healthy men cycled at 50% of V̇O2max in a hot environmental chamber (40°C, 40% relative humidity) until a weight loss of 4.12±0.22% was attained. In the subsequent four hours, subjects ingested one of four solutions at 15-min intervals. The total volume ingested equalled that lost during dehydration. The solutions were administered in randomized order and varied in their carbonation and carbohydrate (CHO) content: 1. CK: carbonated 10% glucose-fructose solution, 2. NCK: non-carbonated 10% glucose-fructose solution, 3. CNK: carbonated non-caloric solution, and 4. NCNK: non-carbonated non-caloric solution. Plasma volume changes, total plasma protein concentration, plasma osmolality, and the plasma glucose concentration were determined at rest before and after dehydration, and at 30, 90, 150, and 240 min of recovery. Plasma volume changes and the plasma protein concentration were not different (p > 0.05) between treatments. Values for the plasma glucose concentration and the change in plasma osmolality were significantly elevated when CHO beverages were ingested when compared with non-CHO beverage ingestion. Five-min cycling bouts were performed at 70% of V̇O2max before and after dehydration and at 60, 120, 180, and 240 min of rehydration. The respiratory exchange ratio was elevated in both of the CHO treatments when compared with both of the non-CHO treatments at 60, 120, 180 and 240 min of rehydration. Lactate determined from arterialized capillary blood obtained one minute after each cycling bout was not different between treatments at any time point. Heart rates during the standardized cycling bouts remained elevated relative to the pre-dehydration values in all treatments after 240 min of recovery despite ingestion of a volume of fluid equal to that lost. In addition, heart rates were significantly elevated in the CK treatment relative to other treatments at 60 (vs CNK and NCNK), 120 (vs CNK and NCNK), 180 (vs NCNK), and 240 min (vs NCK). Rectal temperatures during the cycling bouts were significantly elevated in the carbohydrate treatments relative to the non-carbohydrate treatments at 120 min (CK vs NCNK, NCK vs NCNK) and 180 minutes (CK vs NCNK and CNK) but remained within the normal range (37.3 - 37.6°C). No differences were observed in the % body weight loss or total urine volume after 240 min of recovery. The results suggest that solutions which are carbonated and/or contain 10% CHO are as effective as noncarbonated and non-CHO solutions with regard to fluid replacement over four hours