Abstract
Background: Hypohydration is common across a wide range of sport settings, it has been shown to impair both physical and cognitive performance. Rehydration studies have investigated milk as a rehydration beverage and found that it can be more effective than sports drinks at retaining fluid. The components of milk responsible for this effect are currently not known. However, it is possible that casein protein, the main protein constituent in milk could be responsible, to date there are no studies investigating the effect of casein protein on rehydration.
Objective: To investigate the effect of casein protein on markers of rehydration in comparison to a sports drink and to investigate any palatability differences between the casein and sports drink.
Methods: This was a randomised cross over design study, with 10 healthy male participants. Participants arrived at the clinic in the evening and performed an intermittent cycling protocol until they were dehydrated by 2% bodyweight. They were then given 150% of their weight loss in fluids, separated into four boluses provided every 15 minutes. The initial bolus differed between trials and was either 540 mL of casein protein (containing 20g of protein) or 540 mL of sports drink (5.9% carbohydrates). The remaining three boluses were all equal amounts of water. Hydration status was measured at 1 hour, 2 hours and in the morning post exercise using urine specific gravity and urine osmolality. The net fluid balance was also calculated using fluid intake data and urine output measures. Subjective questionnaires with 100mm analogue scales were used to quantify drink characteristics and to measure any gastrointestinal symptoms, these questionnaires were given at the same time hydration status was measured.
Results: There were no significant differences between the two drinks for urine specific gravity, urine osmolality and net fluid balance (p>0.05). The sports drink was significantly more pleasant and sweeter than the casein drink (p=0.005).
Conclusion: Casein protein alone as a rehydration beverage did not significantly improve or impair rehydration and fluid retention after exercise induced dehydration in comparison to a commercially available carbohydrate -electrolyte sports drink. However, the sports drink was significantly more pleasant and palatable than the casein drink, this may have implications for ad-libitum intakes.