Hydration Dynamics and Influence of Beverage Composition

The study examines interactions between fluid availability in the gut and fluid retention in the body. The relative rate of fluid uptake, the expansion of the plasma volume, and percent of fluid retained by the body will be measured in response to ingestion of beverages of different composition. Healthy, euhydrated adults will be studied. The results will help establish formulations of beverages that sustain if not promote acute euhydration.

Using a randomized order for beverage treatments at three separate trials, subjects will ingest 1 Liter of one of three beverages in 10 minutes: water, a beverage with 2.5% glucose with 45 mmol sodium/L, or a beverage with 1.7% glucose with 60 mmol sodium/L. Before and repeatedly for 2 h after ingestion of the beverage, blood samples will be drawn for assessments of D2O, Hb, Hct, osmolality, sodium, and glucose. The rate of appearance of D2O will be evaluated using the area under the curve, the slope of the appearance, and half time to plateau. Comparisons will be made between beverages for indices of the rate of appearance of D2O, the change in PV over time, and cumulative urine excreted. The cumulative urine produced will be used to calculate a modified BHI for the two glucose-electrolyte beverages and water for comparison with 1.0 (expected for no beverage effect). We hypothesize faster absorption (D2O appearance rate), and better overall hydration (expanded PV and higher modified BHI) will occur for beverages containing glucose and sodium compared to water. Further, we hypothesize that of the electrolyte beverages, the beverage with higher sodium content will promote greater overall hydration (less urine excreted) than the beverage with lower sodium.

Hydration, Deuterium oxide, Plasma osmolality, Sodium, Urine production, Fluid absorption, Euhydration

Measure the rate of fluid uptake by the gut using appearance of deuterium oxide, or D2O, in the blood after ingesting a fixed volume of placebo.

Measure the rate of fluid uptake by the gut using appearance of deuterium oxide, or D2O, in the blood after ingesting a fixed volume of placebo.

Measure the rate of fluid uptake by the gut using appearance of deuterium oxide, or D2O, in the blood after ingesting a fixed volume of placebo.

Measure fluid retention using the difference between ingested volume and cumulative urine excretion as a percentage of the ingested volume.

Measure fluid retention using the difference between ingested volume and cumulative urine excretion as a percentage of the ingested volume.

Measure fluid retention using the difference between ingested volume and cumulative urine excretion as a percentage of the ingested volume.

Inclusion Criteria: Have a BMI of 18.5 to 29.9 kg/m2. Be normotensive (<120/80 mm Hg). Must be able to speak and read English. Be physically active or a regular exerciser but be able to abstain from exercise for 48 h prior to each study trial. Fast for at least 8 hours prior to and through the study trial. Be able to abstain from alcohol for 48 h prior to each study. Be able to abstain from caffeine for 24 h prior to each study. If female, must have regular menstrual cycles, that are > 27 days and < 35 days in length. Exclusion Criteria: Under 18 y of age or over 45 y of age. Have a BMI <18.5 or >30. Being pregnant. Lactating. Tobacco user. Have hypotension or hypertension. Have any type of kidney disease or dysfunction. Have diabetes. Have any type of cardiovascular disease. Have been diagnosed with galactosemia. Females with irregular menstrual cycles. Females with polycystic ovary disease.