Effect of Electrolyte Containing Beverages on Measures of Hydration During Rest

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Previous research indicates that electrolyte beverages (chicken noodle soup) ingested before exercise augments fluid balance by increasing ad libitum water intake and reducing urine volume during exercise. However, we are unable to determine whether sodium or other macronutrients contained in the pre-exercise beverages were responsible for this effect. PURPOSE: To determine the efficacy of four different “pre-exercise” beverages on measures of hydration at rest. METHODS: Ten healthy young male ingested 355 ml of one of four experimental beverages: water (W), water with 1355 mg sodium (SW), chicken noodle soup (CS), or V8 vegetable drink (V8).Blood samples were drawn before beverage ingestion and every five minutes for the first 45 minutes and 60, 80, 100 and 120 minutes after ingestion of the beverages. In addition, every time a blood was drawn, subjects recorded their feeling of thirst on an analogue scale. A urine sample was collected prior to beverage ingestion and total urine volumes were measured and analyzed 45 and 120 min after ingestion of the experimental beverage. RESULTS: Urine output was not significant between the trials; however there was a tendency for the mean of the urine output in V8 and W to be greater than CS and SW. The same tendency for the mean of the urine output was observed between trials by time (p < 0.07). Beverages that produced high urine volumes also produced less concentrated urine shown by lower urine specific gravity (trial × time; p = 0.006). A trial effect exists for percent change in plasma volume (p < 0.001). Further analyses using Holm-Sidak's comparisons revealed significant differences in CS vs. V8 and W and between SW vs. W and V8. Thirst responses over time were different by the experimental beverage (p < 0.007), but none of the individual trials differed at any time point. CONCLUSIONS: The CS and SW beverage induced reduction of urine output and increased plasma volume and thirst response, indicating that sodium concentration is more important than other beverage macronutrients for promoting improve hydration status. In fact the opposite effects on plasma volume, urine volume, and thirst response were observed after water ingestion. The V8 beverage induced reduction of plasma volume and increased urine volume and thirst response, indicating that high potassium concentration in the pre-exercise beverage can interrupt the positive effects on hydration status induced by high sodium concentration. But data showed, also, that V8 beverage before exercise should increased the ingestion of fluid during exercise and so augment the fluid balance.