Does Relative Fluid Delivery Of Beverages Into The Blood Influence Short-term Fluid Retention?

The speed of fluid delivery of beverages into blood appears to be influenced more by macronutrient content than sodium levels; however, fluid retention is influenced by sodium and macronutrient content. PURPOSE: To examine whether the relative “speed” of hydration for beverages entering the blood inversely influences subsequent short-term fluid retention. METHODS: Fifteen healthy men completed a resting deuterium oxide (D2O) tracer ingestion study followed by 2 h beverage hydration index (BHI) protocol. Four beverages with similar [electrolyte] were compared to water: 0% carbohydrate (CHO) + amino acid alanine (AA), 4% CHO and 6% CHO. After ingesting 500 ml tagged with 10 g D2O, blood was sampled over 60 min. The BHI protocol immediately followed with 1 L beverage ingestion (every 7.5 min for 30 min) followed by 2 h serial urine and body mass change measurements. RESULTS: D2O accumulation post-ingestion and half-time to reach peak (t1/2max) were not different among beverages, although water tended (p = 0.09) to be slower than 0% + AA (19.1 ± 5.5 vs. 16.3 ± 6.2 min) and similar to 4%CHO and 6%CHO (18.4 ± 4.9, 18.7 ± 4.2 min, respectively). Peak blood glucose was higher (p < 0.05) for 6%CHO and 4%CHO compared to water and 0%CHO + AA. BHI at 2 h was lower (p < 0.05) for water (1.0 reference value) and 0%CHO + AA (1.07 ± 0.16) compared to 6%CHO (1.42 ± 0.32) but not different from 4%CHO (1.19 ± 0.28). Net fluid balance was lower (p < 0.05) for water compared to 6%CHO; however, 0%CHO + AA was lower compared to both 4%CHO and 6%CHO. CONCLUSIONS: Inclusion of sodium in an amino acid drink without carbohydrate did not improve acute fluid bioavailability compared to water. Moreover, the alanine beverage with sodium exhibited lower net fluid balance compared to 6% and 4% carbohydrate beverages with similar electrolyte levels. The speed of beverage appearance into the blood was not associated with subsequent short-term fluid retention. Supported by: Funded by The Coca-Cola Company