Effect of Electrolyte Addition to Rehydration Drinks Consumed After Severe Fluid and Energy Restriction

This study examined the effect of electrolyte addition to drinks ingested after severe fluid and energy restriction (FER). Twelve subjects (6 male and 6 female) completed 3 trials consisting of 24-hour FER (energy intake: 21 kJ·kg body mass; water intake: 5 ml·kg body mass), followed by a 2-hour rehydration period and a 4-hour monitoring period. During rehydration, subjects ingested a volume of drink equal to 125% of the body mass lost during FER in 6 aliquots, once every 20 minutes. Drinks were a sugar-free lemon squash (P) or the P drink with the addition of 50 mmol·L sodium chloride (Na) or 30 mmol·L potassium chloride (K). Total void urine samples were given before and after FER and every hour during rehydration and monitoring. Over all trials, FER produced a 2.1% reduction in body mass and negative sodium (-67 mmol), potassium (-48 mmol), and chloride (-84 mmol) balances. Urine output after drinking was 1627 (540) ml (P), 1391 (388) ml (K), and 1150 (438) ml (Na), with a greater postdrinking urine output during P than Na (p ≤ 0.05). Ingestion of drink Na resulted in a more positive sodium balance compared with P or K (p < 0.001), whereas ingestion of drink K resulted in a more positive potassium balance compared with P or Na (p < 0.001). These results demonstrate that after 24-hour FER, ingestion of a high sodium drink results in an increased sodium balance that augments greater drink retention compared with a low electrolyte placebo drink.