Voluntary Fluid Intake with Milk or Chocolate Milk in Boys Exercising in the Heat

Abstract

The main goal of this study was to compare fluid balance (FB) and voluntary intake (VI) in 10-to 14-year-old boys, when they combine partially skimmed milk or chocolate milk with water during exercise in the heat, as an alternative to using sports drinks. In addition, palatability and gastrointestinal (GI) symptoms were compared. Methods: Thirty-one boys from a junior soccer team (12.6 ± 1.4 y.o., 42.69 ± 2.09 kg and 147.8 ± 10.0 cm) (Mean ± S.D.), exercised in a controlled environment chamber (31.6 ± 0.36 °C dry bulb and 47.3 ± 2% relative humidity), at 67.4 ± 4.1% HRmax using a cycle ergometer and a treadmill. They alternated 20 minutes of exercise with 10 minutes of rest on four consecutive times, for a total of 120 minutes in the chamber. Ad libitum fluid intake was monitored from the simultaneous presentation of water and partially skimmed milk (session A), or water and partially skimmed chocolate milk (session B); the drinks had a temperature of 15.9 ± 0.12°C. Fluid balance was calculated from differences in nude body weight. Palatability and GI symptoms were reported upon arrival, and before, during, and at the end of the exercise session. Results: No significant differences were found in the initial conditions between sessions A and B. No significant difference was found between sweat rates during session A (460.8±217.4 mL*h-1) and session B (459.8±229.4 mL*h-1) (p = 0.98). FB was the same for both sessions (0.76 ± 0.80 %BW vs. 0.77 ± 0.76 %BW, p = 0.94). A significant difference was found in time: a positive FB (overhydration) was observed during the first hour of exercise, but not during the second hour. VI was the same for both sessions (p = 0.87), but different over time: boys drank more fluid during the first hour (573 and 526 mL for sessions A and B, respectively) than during the second hour (307 and 343 mL for A and B, respectively) (p<0.001). Chocolate milk showed the highest palatability scores and water showed the lowest. GI symptoms were low. Conclusion: When presented simultaneously with water, both partially skimmed milk and chocolate milk were effective in preventing voluntary dehydration in boys exercising in the heat. Palatability scores were favorable and GI symptoms were not clinically relevant.