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Water-Induced Thermogenesis Reconsidered: The Effects
of Osmolality and Water Temperature on Energy
Expenditure after Drinking
Clive M. Brown, Abdul G. Dulloo, and Jean-Pierre Montani
Department of Medicine, Division of Physiology, University of Fribourg, 1700 Fribourg, Switzerland
Context: 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, de-
termine whether the response is influenced by osmolality or by water
temperature.
Design: This was a randomized, crossover design.
Setting: The study was conducted at a university physiology laboratory.
Participants: Participants included healthy young volunteer
subjects.
Intervention: Intervention included drinking 7.5 ml/kg body weight
(⬃518 ml) of distilled water or 0.9% saline or 7% sucrose solution
(positive control) on different days. In a subgroup of subjects, re-
sponses to cold water (3 C) were tested.
Main Outcome Measure: 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 the-
oretical energy cost of warming the water to body temperature.
These results cast doubt on water as a thermogenic agent for
the management of obesity. (J Clin Endocrinol Metab 91:
3598 –3602, 2006)
T
HE HIGH PREVALENCE of overweight and obesity has
led to the search for compounds that can increase en-
ergy expenditure and fat oxidation, thereby promoting
weight loss. Because thermogenesis is partly regulated by
sympathetic activity, substances that interact with the sym-
pathetic nervous system can be considered as potential
agents for weight reduction (1). Sympathomimetic com-
pounds such as ephedrine are effective at increasing ther-
mogenesis (2) but can have undesirable side effects (3). Safe,
preferably nonpharmacological substances that can stimu-
late thermogenesis without causing side effects are therefore
sought. A surprising candidate for a thermogenic agent is
one of the most essential of all substances required for life:
water. Drinking half a liter of water increases activity of the
sympathetic nervous system as measured by enhanced
plasma norepinephrine levels (4) and muscle sympathetic
nerve activity (5). Boschmann et al. (6) hypothesized that the
sympathetic activation after water drinking might stimulate
thermogenesis. They reported that drinking 500 ml of water
increased resting energy expenditure by 30%. The response
started within 10 min of drinking the water, peaked at 30 –40
min, and was sustained for more than an hour (6). The
water-induced thermogenesis was attributed to sympathetic
nervous system activation because ingestion of a

-adreno-
receptor blocker before drinking almost completely abol-
ished the response. Drinking water that had been heated to
37 C attenuated the thermogenic response by 40%, which led
to the suggestion that water-induced thermogenesis could be
partly attributed to the energy cost of warming the water to
body temperature (6). The authors extrapolated that increas-
ing daily water intake by 1.5 liters would augment energy
expenditure by approximately 200 kJ/d (6). If confirmed,
water-induced thermogenesis would have important impli-
cations for weight control programs. However, the concept
of water-induced thermogenesis is controversial. Several
studies in humans (7–16) have reported that water drinking
has little or no effect on resting energy expenditure (Table 1).
We therefore undertook the present study to further in-
vestigate the concept of water-induced thermogenesis. To
eliminate the possibility that dissolved impurities or other
substances in tap or mineral water might contribute to ther-
mogenesis, we used distilled water. On the basis that osmo-
lality might have a role in water-induced thermogenesis, we
also tested responses to physiological (0.9%) saline. As a
positive control, thermogenic responses were measured after
ingestion of the same volume of a 7% sucrose solution. Fi-
First Published Online July 5, 2006
Abbreviations: BMI, Body mass index; RQ, respiratory quotient;
VCO
2
, carbon dioxide production; VO
2
, oxygen consumption.
JCEM is published monthly by The Endocrine Society (http://www.
endo-society.org), the foremost professional society serving the en-
docrine community.
0021-972X/06/$15.00/0 The Journal of Clinical Endocrinology & Metabolism 91(9):3598–3602
Printed in U.S.A. Copyright © 2006 by The Endocrine Society
doi: 10.1210/jc.2006-0407
3598
nally, considering the suggestion that part of water-induced
thermogenesis might be attributed to the energy required to
warm the water to body temperature, we tested whether
ingestion of cold water would augment the thermic response.
Subjects and Methods
Subjects
Responses to ingestion of distilled water, 0.9% saline, and 7% sucrose
were measured in eight healthy volunteer subjects [six males, two fe-
males; aged 25 ⫾ 1 yr; height 176 ⫾ 3 cm; weight 69 ⫾ 2 kg; body mass
index (BMI) 22.5 ⫾ 0.7 kg/m
2
]. Statistical analysis showed that this
number of subjects was sufficient to detect, at a significance level (alpha)
of 0.05 and power (1-beta) of 0.96, a change in resting energy expenditure
of 6% with a sd of the response of 5%. Time-control experiments were
performed in five subjects (three males, two females; aged 26 ⫾ 2 yr;
height 176 ⫾ 3 cm; weight 64 ⫾ 3 kg; BMI 20.8 ⫾ 0.7 kg/m
2
). In six healthy
subjects (five males, one female; age 27 ⫾ 1 yr; height 179 ⫾ 3 cm; weight
66 ⫾ 3 kg; BMI 20.8 ⫾ 0.6 kg/m
2
), we assessed responses to ingestion of
cold water (3 C). None of the subjects had any diseases or were taking
medications. The subjects were requested to avoid doing physical exercise,
refrain from caffeine consumption for at least 24 h, and have nothing to eat
for 12 h and nothing to drink for 2 h before the experiments. Written
informed consent was obtained from each subject according to the Decla-
ration of Helsinki. The study protocol was approved by the institutional
ethics committee.
Protocol
All measurements were performed in the morning, starting at 0830–
0930 h, in a temperature-controlled (21 C) quiet room with the subjects
in a comfortable seated position.
Ingestion of distilled water, 0.9% saline, and 7% sucrose. The subjects at-
tended three experimental sessions according to a randomized crossover
design. Respiratory gas exchange was measured by indirect calorimetry
using an open-circuit ventilated hood system (Deltatrac monitor; Datex,
Helsinki, Finland). Resting energy expenditure and respiratory quotient
(RQ) were derived from the rates of oxygen consumption (VO
2
) and
carbon dioxide production (VCO
2
) using the Weir equation (17). The
precision of the gas analyzers, the calibration procedure, and the accu-
racy of the entire ventilated-hood system were regularly determined by
ethanol combustion tests lasting between 2 and 4 h. These ethanol tests
yield values for RQ of 0.67, with a coefficient of variation less than 2%
and differences between calculated and measured energy expenditure
of less than 3%. After an initial resting period of 30 – 40 min to allow gas
exchange values to reach a steady state, resting energy expenditure was
measured over 30 min. Then subjects ingested 7.5 ml/kg body weight
(mean volume 518 ⫾ 16 ml) of distilled water, 0.9% saline, or a 7%
sucrose solution over 3 min. The drinks were served at room temper-
ature. Gas exchange measurements were continued for a further 90 min
after the drink. Values were recorded every minute and then averaged
over 10-min intervals.
Time-control experiment. In five volunteers we tested the effects of a sham
drink. After resting energy expenditure was recorded over a 30-min
period, the subjects raised a vessel containing water (7.5 ml/kg body
weight) to their lips but did not ingest any of the water. Resting energy
expenditure was recorded for a further 90 min after the sham drink.
Ingestion of cold water. In a subgroup of six subjects, we tested the effects
of ingesting distilled water (7.5 ml/kg body weight, mean volume 4.95
ml) that had been cooled to 3 C.
Statistical analysis
All data are given as means ⫾ sem. Responses to the distilled water,
0.9% saline, and 7% sucrose drinks were tested by ANOVA for repeated
measures. The postdrink values at 10-min time intervals were compared
with values recorded during the 30-min baseline period using Dunnett’s
test for multiple comparisons. Total changes in energy expenditure
(areas under the curve) after the three drinks were compared by
ANOVA for repeated measures with Tukey’s post hoc test to compare
pairs of drinks. Energy expenditure after ingestion of cold water was
compared with the corresponding baseline value by a paired t test. The
statistics were performed using statistical software (InStat version 3.01;
GraphPad Software, San Diego, CA). The level of statistical significance
was set at P ⬍ 0.05.
Results
Responses to distilled water, 0.9% saline, and 7% sucrose
Resting values of VO
2
, VCO
2
, resting energy expenditure,
and RQ as recorded over 30 min before ingestion of each of
the drinks were similar and are shown in Table 2. The time
courses of the responses to the three drinks are shown in Fig.
1. Ingestion of distilled water did not significantly affect VO
2
(P ⫽ 0.20), VCO
2
(P ⫽ 0.60), resting energy expenditure (P ⫽
0.34), or RQ (P ⫽ 0.14). Similarly, ingestion of 0.9% saline had
no significant effects on VO
2
(P ⫽ 0.30), VCO
2
(P ⫽ 0.15),
resting energy expenditure (P ⫽ 0.33), or RQ (P ⫽ 0.14). In
contrast, ingestion of 7% sucrose resulted in a significant and
sustained increase in VO
2
, VCO
2
, resting energy expendi
-
TABLE 1. Summary of several published studies measuring acute changes in energy expenditure after water drinking in humans
Study
Year of
publication
Water volume
No. of
subjects
Calorimetry
method
Reported increase in
energy expenditure?
Boschmann et al. (6) 2003 500 ml 14 Whole room 30% increase after 60 min
Brundin and Wahren (7) 1993 375 ml 7 Ventilated hood 2% increase over 2 h
De Jonge et al. (8) 1991 Not stated
a
9 Ventilated hood No
Dulloo and Miller (9) 1986 200 ml 8 Douglas bag No
Felig et al. (10) 1983 400 ml 3 Ventilated hood No
Gougeon et al. (11) 2005 750 ml 2 Ventilated hood No
Komatsu et al. (12) 2003 300 ml 8 Douglas bag 2.7% increase over 2 h
LeBlanc et al. (13) 1984 600 ml 8 Pneumotachograph No
Li et al. (14) 1999 280 ml 19 Ventilated hood No
Paolisso et al. (15) 1997 Not stated 8 Ventilated hood No
Sharief and Macdonald (16) 1982 4 ml/kg ideal body weight
(average 292 ml)
6 Ventilated hood No
a
But at least 410 ml.
TABLE 2. Resting values of gaseous exchange parameters and
resting energy expenditure recorded over 30 min immediately
before ingestion of the water, saline, and sucrose drinks
Water Saline Sucrose
VO
2
(ml/min)
224 ⫾ 14 218 ⫾ 13 228 ⫾ 14
VCO
2
(ml/min)
199 ⫾ 13 190 ⫾ 11 193 ⫾ 12
Resting energy expenditure
(kJ/min)
4.53 ⫾ 0.29 4.40 ⫾ 0.26 4.58 ⫾ 0.28
RQ 0.89 ⫾ 0.02 0.87 ⫾ 0.02 0.85 ⫾ 0.02
Brown et al. • Water-Induced Thermogenesis Reconsidered J Clin Endocrinol Metab, September 2006, 91(9):3598 –3602 3599
ture, and RQ (all P ⬍ 0.0001). The average 90-min increase
in resting energy expenditure (area under the curve) after the
sucrose drink was 33 ⫾ 4 kJ, compared with ⫺2 ⫾ 6 kJ after
the distilled water drink and 7 ⫾ 5 kJ after the saline drink
(ANOVA, P ⫽ 0.0002; Tukey post hoc test, water vs. saline, P ⬎
0.05; water vs. sucrose, P ⬍ 0.001; saline vs. sucrose, P ⬍ 0.01).
Individual responses to ingestion of the water and sucrose
drinks are compared in Fig. 2.
Time-control experiment
Responses to ingestion of the sham drink are included in
Fig. 1. The coefficient of variation for resting energy expen-
diture over the entire 2-h recording period was 2.3% (1.9%
before the sham drink and 2.4% after the sham drink). By
comparison, for the water drink, the coefficient of variation
for resting energy expenditure was 3.0% over the 2-h re-
cording period (2.0% before the drink and 2.7% after the
drink).
Responses to cold water
Drinking distilled water that had been cooled to3Cin-
creased resting energy expenditure in all six subjects (Fig. 3),
from 4.48 ⫾ 0.24 to 4.69 ⫾ 0.23 kJ/min (P ⫽ 0.0068) over 60
min. The total increase in resting energy expenditure (area
under the curve) after 3 C water ingestion was 13 ⫾ 3 kJ after
60 min and 15 ⫾ 3 kJ after 90 min.
Discussion
It was reported that drinking half a liter of water at room
temperature increased resting energy expenditure by 30%
after an hour (6). This previously unrecognized thermogenic
property of water was suggested as a potential means for
increasing energy expenditure in the treatment of obese and
FIG. 1. Changes in VO
2
(A), VCO
2
(B), resting energy
expenditure (REE) (C), and RQ (D) after drinking
distilled water, 0.9% saline, or a 7% sucrose solution.
Responses to a sham drink are also plotted. The
drinks were ingested at time 0 min. Data points rep-
resent the mean value over the preceding 10 min (*,
P ⬍ 0.05; **, P ⬍ 0.01).
FIG. 2. Integrated changes in resting energy expenditure (REE) over
90 min in individual subjects after drinking water or a 7% sucrose
solution (**, P ⬍ 0.01).
3600 J Clin Endocrinol Metab, September 2006, 91(9):3598 –3602 Brown et al. • Water-Induced Thermogenesis Reconsidered
overweight individuals (6). The current study was designed
to reassess water-induced thermogenesis and investigate
whether osmolality or water temperature might influence
energy expenditure after drinking. Our results are, however,
inconsistent with the concept of water-induced thermogen-
esis. Resting energy expenditure remained unchanged after
drinking distilled water or a 0.9% saline solution. Drinking
water that had been cooled to 3 C increased resting energy
expenditure by only about 5%. In contrast, ingestion of a 7%
sucrose solution increased resting energy expenditure by 33
kJ over 90 min. This amounts to about 5% of the energy
content of the sucrose and is in line with the dietary-induced
thermogenesis reported elsewhere after carbohydrate inges-
tion (7, 14).
Boschmann et al. (6) reported that drinking water that had
been warmed to 37 C reduced the postdrink increase in
energy expenditure by 40%. The extent of this attenuation in
water-induced thermogenesis closely matched the calculated
energy required to heat the water from room temperature to
body temperature (about 30 kJ for 500 ml) (6). On that basis,
drinking cold water should augment the thermogenic effect.
Indeed, we found that drinking distilled water that had been
cooled to 3 C slightly increased resting energy expenditure
by an average of 15 kJ over 90 min. However, this is sub-
stantially lower than the calculated energy required to heat
the water from 3 to 37 C (495 ml ⫻ 34 C ⫽ 16830 cal ⫽ 70 kJ),
suggesting that most of the energy required for warming the
water to body temperature is more likely to be met by a
reduction in body heat loss, probably by the peripheral va-
soconstriction that occurs after water drinking (5).
The 30% increase in energy expenditure after water drink-
ing reported by Boschmann et al. (6) is impressive, but it is
not supported by previously published studies (7–16) or the
results of the current study. What could be the explanation
for the apparent water-induced thermogenesis? One clue
could be in the fact that Boschmann et al. (6) measured energy
expenditure by whole-room indirect calorimetery, as op-
posed to the ventilated hood or mouthpiece techniques that
we and others (7–16) have used. Ventilated hood and mouth-
piece apparatus have a small dead space, thereby permitting
rapid attainment of steady-state gas concentrations. In con-
trast, whole-room calorimeters may require1hormore to
attain steady-state conditions because of their large size in
relation to ventilation rate (18) and are therefore less suitable
for acute measurements. Boschmann et al. (6) used a run-in
period of only 15 min before starting to measure resting
energy expenditure. It is possible that their data reported
from 30 min later, after water drinking, might be a conse-
quence of a slow response time of the whole-room calorim-
eter and simply reflect earlier activities within the chamber.
Unfortunately, Boschmann et al. (6) did not provide any
information about the size of their chamber or the time re-
quired to reach a steady state.
Water-induced thermogenesis might also result from sub-
stances dissolved in the water. Boschmann et al. (6) did not
state in their paper whether they used tap water, bottled
water, or distilled water. Tap water and bottled water contain
a number of dissolved electrolytes and impurities that could
potentially stimulate a thermogenic effect. In the current
study, we excluded this possibility by using distilled water.
Various studies have indicated that drinking half a liter of
water increases the activity of the sympathetic nervous sys-
tem (4, 5). The hypothesis that water drinking might also
stimulate the metabolism therefore seems reasonable. It is,
however, important to note that sympathetic activation does
not uniformly affect all physiological functions. Sympathetic
nervous system activity to several organs (such as heart,
liver, kidneys, and pancreas) is increased in response to diet,
but it is uncertain as to whether they contribute to dietary-
induced thermogenesis (19). An increase in sympathetic ac-
tivity to skeletal muscle has been reported after water drink-
ing (5). Yet in humans, infusion of norepinephrine does not
result in a detectable increase in thermogenesis in forearm
skeletal muscle (20). Therefore, sympathetic activation ob-
served after water drinking (particularly to skeletal muscle)
might not necessarily lead to an increase in metabolic rate.
Instead, the increase in sympathetic neural activity after wa-
ter drinking is accompanied by peripheral vasoconstriction
and a reduction in limb blood flow (5).
The confirmation of water-induced thermogenesis would
have important public health implications, not least because
water drinking might be useful as a safe, cheap, and non-
pharmacological method of reducing weight. Using an ex-
perimental setup capable of rapidly detecting small changes
in energy expenditure, we were unable to find a thermogenic
effect of distilled water at room temperature. Consequently,
our results cast doubt on a role for water as a thermogenic
agent in the management of obesity.
Acknowledgments
Received February 22, 2006. Accepted June 27, 2006.
Address all correspondence and requests for reprints to: Dr. Clive M.
Brown, Department of Medicine, Division of Physiology, University of
Fribourg, Rue du Muse´e 5, 1700 Fribourg, Switzerland. E-mail:
clivemartin.brown@unifr.ch.
This work was supported by grants from the Swiss Foundation for
Nutrition Research and the Swiss Heart Foundation.
Author disclosure summary: C.M.B., A.G.D., and J.-P.M. have noth-
ing to declare.
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3602 J Clin Endocrinol Metab, September 2006, 91(9):3598 –3602 Brown et al. • Water-Induced Thermogenesis Reconsidered