Hanley, L. J., Bolster, D. R., Pikowsky, M. A., Bennett, B. T., Maresh, C. M., Armstrong, L. E., Seen, A., Sinston, C., & Rodriguez, N. R. (2001). Effects of increased dietary protein intake on fluid balance indices in endurance runners. Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 786.

Hydration status in endurance runners (N = 6) was evaluated under two conditions; high (3.6 g/kg) protein intake or moderate (1.8 g/kg) intake, each condition lasting four weeks. The percentages of carbohydrate, protein, and fat for the two conditions were 40-30-30% and 55-15-30% respectively.

Body mass and fluid intake did not change during or between conditions. Urine specific gravity and blood urea nitrogen were significantly higher in the high intake condition. Plasma osmolality was significantly higher pre- and post-exercise in the high-intake condition.

Implication. Fluid balance is not influenced by a short-term (e.g., four weeks) increase in protein intake. However, what would happen over longer periods is not known and extensive periods of increased protein intake should be monitored closely and undertaken with caution.

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