Water-induced thermogenesis and fat oxidation: a reassessment

BACKGROUND/OBJECTIVES Drinking large amounts of water is often recommended for weight control. Whether water intake stimulates energy and fat metabolism is, however, controversial with some studies reporting that drinking half a litre or more of water increases resting energy expenditure (REE) by 10-30% and decreases respiratory quotient (RQ), whereas others report no significant changes in REE or RQ. The aim here was to reassess the concept of water-induced thermogenesis and fat oxidation in humans, with particular focus on interindividual variability in REE and RQ responses, comparison with a time-control Sham drink, and on the potential impact of gender, body composition and abdominal adiposity. SUBJECTS/METHODS REE and RQ were measured in healthy young adults (n=27; body mass index range: 18.5-33.9 kg m(-2)), by ventilated hood indirect calorimetry for at least 30 min before and 130 min after ingesting 500 ml of purified (distilled) water at 21-22 °C or after Sham drinking, in a randomized cross-over design. Body composition and abdominal fat were assessed by bioimpedance techniques. RESULTS Drinking 500 ml of distilled water led to marginal increases in REE (<3% above baseline), independently of gender, but which were not significantly different from Sham drinking. RQ was found to fall after the water drink, independently of gender, but it also diminished to a similar extent in response to sham drinking. Interindividual variability in REE and RQ responses was not associated with body fatness, central adiposity or fat-free mass. CONCLUSIONS This study conducted in young men and women varying widely in adiposity, comparing the ingestion of distilled water to Sham drinking, suggests that ingestion of purified water per se does not result in the stimulation of thermogenesis or fat oxidation.