Water-induced thermogenesis reconsidered: the effects of osmolality and water temperature on energy expenditure after drinking.
BACKGROUND
A recent study reported that drinking 500 ml of water causes a 30% increase in metabolic rate. If verified, this previously unrecognized thermogenic property of water would have important implications for weight-loss programs. However, the concept of a thermogenic effect of water is controversial because other studies have found that water drinking does not increase energy expenditure.


OBJECTIVE
The objective of the study was to test whether water drinking has a thermogenic effect in humans and, furthermore, determine whether the response is influenced by osmolality or by water temperature.


METHODS
This was a randomized, crossover design.


METHODS
The study was conducted at a university physiology laboratory.


METHODS
Participants included healthy young volunteer subjects.


METHODS
Intervention included drinking 7.5 ml/kg body weight (approximately 518 ml) of distilled water or 0.9% saline or 7% sucrose solution (positive control) on different days. In a subgroup of subjects, responses to cold water (3 C) were tested.


METHODS
Resting energy expenditure, assessed by indirect calorimetry for 30 min before and 90 min after the drinks, was measured.


RESULTS
Energy expenditure did not increase after drinking either distilled water (P = 0.34) or 0.9% saline (P = 0.33). Drinking the 7% sucrose solution significantly increased energy expenditure (P < 0.0001). Drinking water that had been cooled to 3 C caused a small increase in energy expenditure of 4.5% over 60 min (P < 0.01).


CONCLUSIONS
Drinking distilled water at room temperature did not increase energy expenditure. Cooling the water before drinking only stimulated a small thermogenic response, well below the theoretical energy cost of warming the water to body temperature. These results cast doubt on water as a thermogenic agent for the management of obesity.
Brown
Clive M
CM
Department of Medicine, Division of Physiology, University of Fribourg, Rue du Musée 5, 1700 Fribourg, Switzerland. clivemartin.brown@unifr.ch
Dulloo
Abdul G
AG
Montani
Jean-Pierre
JP
D000328:Adult; D002153:Calorimetry, Indirect; D018592:Cross-Over Studies; D004326:Drinking / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D011897:Random Allocation; D022722:Thermogenesis / Q000502:physiology*; D014867:Water / Q000502:physiology*
D014867:Water