Post-exercise rehydration: Comparing the efficacy of three commercial oral rehydration solutions

Abstract

IntroductionThis study compared the efficacy of three commercial oral rehydration solutions (ORS) for restoring fluid and electrolyte balance, after exercise-induced dehydration.MethodHealthy, active participants (N = 20; ♀ = 3; age ∼27 y, V˙O2peak ∼52 ml/kg/min) completed three randomised, counterbalanced trials whereby intermittent exercise in the heat (∼36°C, ∼50% humidity) induced ∼2.5% dehydration. Subsequently, participants rehydrated (125% fluid loss in four equal aliquots at 0, 1, 2, 3 h) with a glucose-based (G-ORS), sugar-free (Z-ORS) or amino acid-based sugar-free (AA-ORS) ORS of varying electrolyte composition. Urine output was measured hourly and capillary blood samples collected pre-exercise, 0, 2 and 5 h post-exercise. Sodium, potassium, and chloride concentrations in urine, sweat, and blood were determined.ResultsNet fluid balance peaked at 4 h and was greater in AA-ORS (141 ± 155 ml) and G-ORS (101 ± 195 ml) than Z-ORS (−47 ± 208 ml; P ≤ 0.010). Only AA-ORS achieved positive sodium and chloride balance post-exercise, which were greater for AA-ORS than G-ORS and Z-ORS (P ≤ 0.006), as well as for G-ORS than Z-ORS (P ≤ 0.007) from 1 to 5 h.Conclusionwhen provided in a volume equivalent to 125% of exercise-induced fluid loss, AA-ORS produced comparable/superior fluid balance and superior sodium/chloride balance responses to popular glucose-based and sugar-free ORS.

Compositional Aspects of Beverages Designed to Promote Hydration Before, During, and After Exercise: Concepts Revisited

“…Sports drinks (often labeled as “isotonics” regardless of their osmolality) typically consist of isotonic or hypertonic solutions containing higher carbohydrate and lower electrolyte levels than ORS and are formulated for different purposes such as accelerating rehydration and enhancing fluid absorption but also providing easily digested energy during exercise [ 33 ]. On the other hand, ORS, which are hypotonic solutions, were originally conceived for the management of diarrhea-induced dehydration [ 36 ], but recent research has explored their potential role in improving hydration outcomes in exercise (as elaborated in later sections) [ 37 , 38 , 39 , 40 , 41 ]. Importantly, although ORS formulations were standardized by the World Health Organization (WHO) to contain 75 mmol/L sodium (range 60–90 mmol/L) among different compositional factors [ 42 ], other expert organizations such as the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) and the American Academy of Pediatrics (AAP) allow lower sodium levels (45–60 mmol/L) for the management of mild to moderate dehydration due to acute diarrhea [ 43 , 44 ], which may be compatible with compositions recommended by expert institutions in the field of sports.…”

“…Subsequent studies showed a limited effect of rehydrating with l-alanyl-l-glutamine in terms of fluid balance or exercise performance compared to water [ 145 ], while others have supported a role in improving cognitive performance during intermittent sport, albeit no data on hydration/rehydration outcomes were reported [ 146 ]. Regarding amino acid-based ORS, a recent study compared the efficacy of a glucose-based ORS, a glucose-free ORS, and an amino acid-based glucose-free ORS on post-exercise rehydration when consumed at a volume of 125% BML [ 39 ]. Notably, authors observed that both glucose-based and amino acid-based glucose-free formulas restored fluid balance to a similar extent and better than the glucose-free beverage [ 39 ].…”

“…Regarding amino acid-based ORS, a recent study compared the efficacy of a glucose-based ORS, a glucose-free ORS, and an amino acid-based glucose-free ORS on post-exercise rehydration when consumed at a volume of 125% BML [ 39 ]. Notably, authors observed that both glucose-based and amino acid-based glucose-free formulas restored fluid balance to a similar extent and better than the glucose-free beverage [ 39 ]. Lastly, it is possible that amino acid-based beverages might deliver additional benefits such as improved maintenance of the gastrointestinal epithelium during exercise-induced heat stress [ 147 ].…”

“…However, the levels of sodium contained in these CES are typically insufficient to match sweat sodium losses in high-intensity or long-duration scenarios, and the type or amounts of carbohydrates used to sustain fuel needs might not be optimal for effectively restoring plasma volume. Consequently, the use of ORS, with lower carbohydrate (i.e., 2–6%) and higher sodium content (i.e., ≥45 mmol/L), has gained momentum in recent years for improving hydration in exercise settings where compensating sweat losses should be prioritized [ 37 , 38 , 39 , 40 , 41 ]. Likewise, these hypotonic formulas are consistently reported to have higher BHI than sports drinks due to their elevated sodium content, which makes them an attractive choice in professional or clinical situations where fluid availability is limited or urine excretion should be avoided [ 27 , 28 , 30 ].…”