Abstract:
Background: Research suggests that water consumption leads to increased activity of the sympathetic nervous system as shown by increases in heart rate, blood pressure, and increased blood norepinephrine levels. Increased sympathetic activity results in changes in resting metabolic rate (RMR) including energy expenditure and substrate oxidation. Previous research has indicated that water consumption may be used as a means to increase RMR, however the research is limited and inconclusive. The objective of this study is to determine the effects of water ingestion on resting metabolic rate.
Methods: This was a cross-over study of 16 (M=6, F=10) healthy (BMI: 22.8 ± 1.9 kg/m2) adult (age: 25.9 ± 5.5 years) subjects that ingested 250 mL and 500 mL of water after 30 minutes of baseline measures of resting metabolic rate (RMR), the order of water was randomized. RMR was measured using a metabolic cart (QuarkRMR, Cosmed, Rome, Italy) and continued for 90 minutes following water consumption. Body composition was assessed using Dual-energy X-ray Absorptiometry (Horizon, Hologic,Bedford, MA). Hydration status was measured using both a urine color chart (Human Hydration, LLC, Hampton, VA) and by urine specific gravity (Fisher Scientific, 13-946-27).
Results: Our results indicated that water consumption had a metabolic impact. There was a significant (p=0.022) increase in resting energy expenditure (50.4 ±115.9 kcal/ 24hr) over the 90-minute period. There was also a significant (p=0.005) decrease in respiratory quotient from 0.785 ±0.051 at baseline to an average respiratory quotient of 0.770 ±0.046 over the 90 minutes following ingestion of water. Our results showed a statistically significant (p=0.003) 11.4% increase in fat oxidation over the 90-minute period. Both the change in respiratory quotient and fat oxidation were found to be greater after 500 mL of water compared to 250 mL of water (p<0.05). There was no significant correlation between hydration status and change in resting energy expenditure.
Discussion: Our results suggest that ingestion of 500 mL of water could provide a feasible method to increasing fat metabolism during a fasting state and may play a role in weight loss. This study was the first to both evaluate and find a dose-dependent effect of water on resting metabolic rate.
