Post-exercise rehydration: a randomized cross-over trial comparing a 100% fruit juice, a glucose-based sports drink, and water.
BACKGROUND: Previous studies indicate that sports drinks may improve rehydration, compared to water, an effect likely achieved by manufacturing sports drinks to contain carbohydrates and sodium. However, there is a growing preference for natural products and a "food first" approach to sports nutrition. Fruit juices naturally contain similar concentrations of carbohydrates to sports drinks, but fruit juices may produce a more stable blood glucose profile. Fruit juices also naturally contain electrolytes, particularly potassium, but their potential as effective rehydration alternatives to sports drinks, which have higher sodium concentrations, is not well understood. This study compared the rehydration efficacy and glucose responses following consumption of a 100% fruit juice (Raw Hydrate®; FRU), a glucose-based sports drink (SPO), and water (WAT) after exercise-induced hypohydration. Importantly, rehydration beverages were matched for water volume, rather than total volume, to ensure that any potential differences in water balance were not due to unequal water volumes between trials, a limitation affecting previous rehydration research. METHODS: After familiarization, 17 adults (age: 28 ± 8  years; BMI: 23.8 ± 2.9 kg/m2) completed three trials in a randomized cross-over design. The participants cycled in the heat (~35°C) to induce ~2% body mass loss (BML), then rehydrated over a 1 h period in a laboratory (~21°C) with a water volume equivalent to 150% of BML from either FRU, SPO, or WAT. This was followed by an additional 4 h of seated rest (5 h rehydration period), when blood glucose was measured (0, 0.25, 0.5, 0.75, 1, 1.5, and 2 h after beverage consumption), and all urine produced was collected. RESULTS: During the 5 h rehydration period, there was no effect of trial on total urine volume (FRU: 1266 ± 403 mL, SPO: 1338 ± 361 mL, WAT: 1394 ± 360 mL; P = 0.156) or water retention (FRU: 42 ± 12%, SPO: 37 ± 10%, WAT: 35 ± 11%; P = 0.059). The blood glucose area under the curve differed by trial (P < 0.001), with all beverages significantly different from each other (FRU: 10.12 ± 0.72 mmol/L/2h, SPO: 12.48 ± 1.34 mmol/L/2h, WAT: 7.90 ± 0.47 mmol/L/2h; P < 0.003). CONCLUSION: Rehydration efficacy was similar between all beverages, but each elicited a distinct glycemic response. For sports drink consumers seeking a natural alternative or implementing a "food first" nutritional strategy, switching to a 100% fruit juice will not compromise rehydration effectiveness, but may elicit a lower blood glucose response. Although, it should be noted that an additional three participants were withdrawn from the study because of gastrointestinal issues after consuming the 100% fruit juice. This was likely a product of the present study's design, where a large volume of 100% fruit juice (average ~2,300 mL) was consumed in a short period of time (1 h). Whilst this is a commonly used study design to robustly assess the rehydration efficacy of different beverages, future studies should distribute fluid intake over a longer duration, in order to improve ecological validity and reduce the risk of gastrointestinal issues.