Effects of Drink Composition on the Appearance of Ingested Water in Body Fluids

To determine the effects of amino acids on the rate of water absorption and availability as a precursor fluid for sweat. Young and healthy (male or female) volunteers will take part in three experimental trials. In each trial, volunteers will be given one of two commercially available sports drinks or a commercially available sport drink with added amino acids in a double-blinded, randomised, crossover design. Each drink will be a single 550 mL bolus. All beverages will be labelled with deuterium (D2O). Trials will be compared for temporal accumulation of deuterium in plasma over the course of 60 minutes and in urine (60 min). Whole blood measurements of haemoglobin and haematocrit will also be made and plasma volume changes calculated. It is hypothesised that the amino acid trial will increase the rate of fluid absorption.