Hydration plays a crucial role in maintaining physical performance, effective post-exercise
recovery and overall health. For hydration purposes, recreational athletes often use isotonic
beverages, which mostly contain simple sugars. At the same time, excessive sugar intake in
the general population represents a widespread public health issue and is recognised as a risk
factor for obesity, diabetes and cardiovascular disease. The aim of this Master’s thesis was
to investigate the effects of hydration beverages without added simple sugars or other
carbohydrates, but with varying sodium concentrations, on the rehydration process following
physical activity. A single-blind pilot crossover study was conducted in one participant. Over
fifteen experimental days, the participant underwent standardized exercise resulting in 1,5 –
2 % body-mass dehydration, followed by a rehydration phase with five different beverages
with varying sodium concentrations (placebo, 26 mmol/L, 21 mmol/L, 37 mmol/L and 52
mmol/L). The effectiveness of rehydration was assessed using cumulative urine volume after
beverage ingestion, net water and sodium balance, urine specific gravity, and the calculated
beverage hydration index (BHI). Additionally, we monitored heart rate variability (HRV)
and subjective well-being indicators. The results showed that beverages containing 37
mmol/L sodium or more significantly reduce diuresis, increases BHI and improve fluid
retention compared to the placebo. No substantial differences in BHI or cumulative urine
volume were observed between the beverages containing 37 mmol/L and 52 mmol/L sodium.
No statistically significant differences in HRV were observed between the beverages.
Therefore, HRV did not clearly differentiate between the rehydration conditions. The
findings suggest that effective post-exercise rehydration can be achieved with carbohydrate-
and sugar-free electrolyte beverages if they contain an adequate amount of sodium. Because
of the pilot nature of the study and the inclusion of only one participant, the results cannot
be directly generalised. However, they provide a useful basis for further research in larger
samples and contribute to a better understanding of hydration without sugars and
carbohydrates.
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