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PURPOSE: Animal research suggests that variations in daily dietary macronutrient distribution may impact fluid consumption. However, this has not been fully investigated in humans. Thus, the purpose of this study was to determine the impact of dietary intake on fluid intake, thirst, and urinary hydration biomarkers. METHODS: Thirty-four participants (44% female; age: 23±4 years; height: 172.9±10.3cm; body mass: 77.2±18.1kg; body fat: 18.4± 8.4%) recorded their food and fluid intake, and provided a 24h urine sample over seven consecutive days. Urinary hydration biomarkers included urine volume (UVOL), urine osmolality (UOSM), urine specific gravity (USG), and urine color (UCOL). Each morning, participants completed two subjective ratings of perceived thirst; a 9-point Likert scale, and 100mm visual analog scales comprised of six indices (thirstiness, pleasantness, dryness, taste, fullness, sickness). RESULTS: Mean weekly macronutrient percentages and total calorie intake were used in multiple regression models as predictors of average total fluid intake, thirst, and urinary hydration markers. Throughout the week, participants reported consuming, on average, 1945±429 calories (36.5±4.4% fat, 44.3±6.3% carbohydrate, 18.5±4.5% protein) and 2508±1122mL fluid per day. Mean 7-day 24h urinary hydration markers were UVOL:1724±850mL, USG :1.017±0.005, UOSM: 565±212, UCOL: 3.89±0.99. Dietary intake that was higher in percentage of fat consumed was associated with higher ratings of "fullness" on morning thirst scale sub ratings (adj R² = 0.1181, p =0.0167). Consuming a greater proportion of calories from protein was associated with increased UVOL (adj R² = 0.1370, p = 0.0340). However, protein intake was not significantly associated with fluid intake (adj R2 = 0.0569, p = 0.2516), regardless of the type of fluid consumed (p > 0.05). UOSM, USG, UCOL and the other indices of thirst were not associated with macronutrient consumption (p>0.05). CONCLUSION: These results suggest increased consumption of dietary protein intake is associated with improved hydration status based on increased 24h urine volume, with the maintenance of other urinary hydration indices. Grant or Funding Information: This study was funded by a University of North Carolina at Greensboro Office of Research Engagement New Faculty Grant. [ABSTRACT FROM AUTHOR]