Utility of Body Weight, Urine Color, and Thirst Perception (WUT) in Determining Hydration in Young Adults

The primary aim of this study was to assess the efficacy of the weight, urine, and thirst (WUT) framework in predicting dehydration after a body water manipulation protocol, while concurrently determining the individual and interactive contributions of the model components.

The total study sample was 93 participants (female, n = 47), recruited from two institutions. Phase 1 involved collecting daily hydration measures from free-living participants (study 1, 58 participants for 3 d; study 2, 35 participants for 7 d). Phase 2 entailed a 2-h passive heating protocol, where participants from study 2 were randomly assigned to one of three groups that manipulated total body water over 24 h using passive heating and fluid restriction. During each phase, participants provided urine samples, underwent body mass measurements, and completed questionnaires pertaining to thirst perception. Morning and 24-h urine samples were assessed for color, osmolality, and specific gravity. Differences between intervention groups, based on the probability of hydration status, were examined (ANOVA), and ridge regression analysis assessed the relative importance of variables within the WUT model.

The study revealed significant differences among the intervention groups for predicted probability of dehydration, as determined by changes in body mass ( P = 0.001), urine color ( P = 0.044), and thirst perception ( P < 0.001). Binomial ridge regression indicated that changes in body mass (58%) and thirst perception (26%) were the most influential predictors of dehydration.

These data support use of an enhanced version of the WUT model, underscoring the significance of changes in body mass and thirst perception in the assessment of hydration status.