This study compared differences in weight retention and fluid balance between subjects that consumed various fluids at two different temperatures following exercise-induced dehydration. In this study, we found that weight retention was greatest in those subjects that consumed the cool carbohydrate-electrolyte beverage. In general, in terms of amount consumed, cool temperature and carbohydrate-electrolyte fluid were preferred compared to warmer temperature and plain water, respectively.
These findings support data from previous investigations. Engell and Hirsh [16
] previously reported that the preferred water temperature for rehydration is between 15-21
. In another study, subjects that exercised on a treadmill for 6 hours at elevated temperature consumed 15
fluids more than 40
fluids, and flavored beverage was the most preferred [7
]. Maximal fluid intake was previously shown to be accomplished with 15
water, and any colder or warmer temperature resulted in lower overall consumption [13
]. On the other hand, Jung et al. [21
] reported no difference in fluid consumption between chilled water and five ambient temperature beverages during heat exposure. Thus, in general, it is possible that beverage temperature may affect palatability, which in turn may impact the total amount of fluid consumed during voluntary drinking. One concern is the effect of temperature on the rate of gastric emptying. However, several studies have reported no significant differences in gastric emptying rate and volume using a cold temperature fluid [22
The flavor of the drink is also associated with the amount of fluid intake [24
]. Maughan and Leiper [25
] examined the effect of palatability of the rehydration fluid. The investigators provided beverages with four different solute contents after dehydration, and subjects were allowed to drink ad libitum
. After 2 hours of rehydration, subjects drank a greater volume of sports drink and juice mixture than aerated water. This result indicated that subjects the preferred glucose-electrolyte beverages over non-palatable water. Clapp and colleagues [24
] also reported significantly greater fluid consumption of the carbohydrate-electrolyte beverages as compared with colored water when different beverages were provided for consumption ad libitum
during 4 hours of intermittent exercise in a hot environment. Beridot-Therond et al. [28
] also observed slightly higher consumption of sweetened beverages as compared to mineral water in dehydrated subjects. In addition, consumption of flavored beverages maintained at ambient temperature was shown to be greater than that of ambient temperature water [21
]. Animal studies have suggested that altering the sensorial properties of a beverage by adding a sweetener can increase the volume of consumption through increased palatability [29
]. Further, a sweet taste may stimulate the hunger sensation in humans [30
]. Thus, a cool flavored beverage containing both carbohydrates and electrolytes can stimulate palatability, thereby inducing greater voluntary fluid consumption after dehydration.
There are many reports that have compared the effects of both water and solute-containing beverages on body fluid restoration [33
]. It has been well recognized that water ingestion results in prompt dieresis, even during hypohydration, and prevents a return to a normal hydration state [24
]. Maughan and Leiper [33
] demonstrated that there is a strong relationship between the sodium content of an ingested fluid and the rate of fluid restoration. In one study, the volume of urine excretion was smaller upon consumption of electrolyte-containing beverages as compared with electrolyte-free beverages [37
]. It has also been shown that there is plasma volume is recovered faster using a higher sodium content beverage as compared to a lower one [33
]. The present study also demonstrated higher volume retention as indicated by body weight regain using the cold sports drink. When subjects were allowed to drink plain water regardless of temperature, fluid volume retention was low.
In the present study, subjects did not recover their baseline body weights upon voluntary drinking under any of the conditions. Previous studies have reported that a 1.5-fold volume of fluid ingestion per kilogram of body weight loss is necessary to achieve proper rehydration over a short period of time [3
]. This is due to volume expansion and subsequent increased urine production. In the present study, we observed higher volume consumption only with the cool carbohydrate-electrolyte beverage (1.3 kg weight loss during exercise vs. 1.5 L of beverage intake over 90 min). Further, even under these conditions, the volume of fluid consumed was not anywhere near 1.5-fold the volume of fluid lost. It should be noted that the subjects drank ad libitum
. Previous studies also reported that voluntary fluid consumption is not sufficient to replace all fluid losses following dehydration [35
]. In practical terms, drinking beverages to recover from fluid loss might not be feasible under the circumstance of voluntary drinking, especially when the temperature and composition of the beverage are not optimal to the individual. In fact, many studies reported that subjects who drank water equivalent to 100% of the volume of body fluids lost expressed discomfort during ingestion [38
Under the conditions of this study, we did not observe any marginal differences in blood solute concentration. Further, plasma volume did not fully recover to baseline even after 90 min under all conditions. It has been suggested that the composition of the rehydration beverage should optimally contain 5-10% carbohydrates, 20-30 meq/L of sodium, and 2-5 meq/L of potassium [40
]. Here, sodium and potassium ions replace electrolyte losses due to sweating, and sodium further prevents excessive urine production [6
]. During recovery, sodium consumption in fluids not only retains ingested fluids but also helps to stimulate thirst sensation. Under normal circumstances, the consumption of a carbohydrate-electrolyte solution maintains the sodium concentration in the blood as compared to consumption of plain water [41
]. Thus, plain water is not considered to be the optimal solution for replacing water lost during exercise [39
]. In the present study, under all conditions, both plasma volume and osmolality deviated from baseline after 90 min of recovery. This suggests that both volume and blood tonicity may contribute to the stimulation of thirst sensation [17
]. Ironically, a lesser volume of fluids taken in during recovery had the effect of maintaining thirst when drinking water only. One explanation is that there was lower amount of water consumed versus that lost. In addition, hyponatremia, defined as when the blood sodium level is less than 135 mmol/L [4
], induced by excessive drinking of water following 2% body weight reduction was not observed in this study.
In this study, subjects drank greater amounts of cold carbohydrate-electrolyte beverage than plain water and moderate temperature beverage, resulting in greater weight retention. This suggests that cold carbohydrate-electrolyte beverage is favorable for rehydration during recovery when voluntary drinking is applied.