BEVERAGE OSMOLALITY

Abstract

It has been hypothesized that beverage osmolality may influence gastric emptying and fluid delivery. PURPOSE To examine if small differences in the osmolality of a carbohydrate-electrolyte (CE) sports drink would impact fluid delivery, gastrointestinal distress (GI), and exercise performance during prolonged, high-intensity cycling in warm, humid conditions (27°C, 55%RH). METHODS During 120 min of cycling (alternating between 60 and 75%VO2max), 10 trained cyclists ingested 6%CE (360 mosmol/kg), 7%CE (290 mosmol/kg), and 12%CE (380 mosmol/kg) sports drinks. The volume of fluid ingested was 6 ml/kg prior to cycling and 3.5 ml/kg body weight every 15 min during cycling. Relative fluid uptake was assessed by the appearance of deuterium oxide (D2O) in plasma via mass spectroscopy. GI tolerance of beverages was examined using a Visual Analogue Scale. RESULTS Mean (± SD) work completed during the last 5 min of cycling (kJ) was not significantly different (p> 0.05) among 6%CE (93.7 ± 11.6), 7%CE (91.8 ± 14.8), or 12%CE (88.3 ± 15.8). There were no differences in heart rate, % □ plasma volume, blood lactate, serum electrolytes, core temperature, or perceived exertion among beverages. At 120 min of cycling, blood glucose was significantly lower with 6%CE compared to 12%CE(−12.9%) and 7%CE (−5.8%). D2O was significantly lower with 12%CE compared to 6%CE and 7%CE at 10 min and through 95 minutes of cycling. Subjects indicated greater stomach bloating with 12%CE compared to 7%CE and “felt worse” with 12%CE compared to 6%CE and 7%CE. CONCLUSIONS Energy density influences fluid delivery more than beverage osmolality, confirming recommendations that CE beverages ≥ 10% should not be used during exercise in the heat. GI ratings provide concurrent validity for D2O as a useful index of fluid uptake among beverages. Supported by The Coca-Cola Company.