Pediatric Original Article

International Journal of Obesity (2011) 35, 1295–1300; doi:10.1038/ijo.2011.130; published online 12 July 2011

Influence of water drinking on resting energy expenditure in overweight children

G Dubnov-Raz1,5, N W Constantini2,5, H Yariv3, S Nice2 and N Shapira4

  1. 1Exercise, Nutrition and Lifestyle Clinic, The Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel Hashomer, Israel
  2. 2‘Hadassah Optimal’ Sport Medicine Center, Department of Orthopedic Surgery, Hadassah- Hebrew University Medical Center, Jerusalem, Israel
  3. 3School of Nutritional Sciences, The Robert H Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
  4. 4Center for Nutritional Research, Beilinson Campus, Rabin Medical Center, Petah-Tikva, Israel

Correspondence: Dr G Dubnov-Raz, Exercise, Nutrition and Lifestyle Clinic, The Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel Hashomer, Israel. E-mail: gal.dubnov-raz@sheba.health.gov.il

5These authors contributed equally to this paper.

Received 14 September 2010; Revised 4 April 2011; Accepted 31 May 2011; Published online 12 July 2011.

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Abstract

Background:

 

It was previously demonstrated that drinking water significantly elevates the resting energy expenditure (REE) in adults, and that low water intake is associated with obesity and lesser success in weight reduction. This study addressed the potential of water drinking to increase the REE in children, as an additional tool for weight management.

Objective:

 

To examine the effect of drinking water on the REE of overweight children.

Design:

 

A total of 21 overweight, otherwise-healthy children (age 9.9±1.4 years, 11 males) drank 10mlkg−1 cold water (4°C). REE was measured before and after water ingestion, for 66min. The main outcome measure was the change in mean REE from baseline values.

Results:

 

Immediately after drinking water, there was a transient decrease in REE, from a baseline value of 3.32±1.15kilojoule (kJ) per min to 2.56±0.66kJ per min at minute 3 (P=0.005). A subsequent rise in REE was then observed, which was significantly higher than baseline after 24min (3.89±0.78kJ/min (P=0.021)), and at most time points thereafter. Maximal mean REE values were seen at 57min after water drinking (4.16±1.43kJ per min (P=0.004)), which were 25% higher than baseline. REE was significantly correlated with age, height, weight and fat-free mass; the correlations with maximal REE values after water drinking were stronger than with baseline REE values.

Conclusions:

 

This study demonstrated an increase of up to 25% in REE following the drinking of 10mlkg−1 of cold water in overweight children, lasting for over 40min. Consuming the recommended daily amount of water for children could result in an energy expenditure equivalent to an additional weight loss of about 1.2kg per year. These findings reinforce the concept of water-induced REE elevation shown in adults, suggesting that water drinking could assist overweight children in weight loss or maintenance, and may warrant emphasis in dietary guidelines against the obesity epidemic.

Keywords:

energy expenditure; fluids; metabolic rate; pediatrics

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Introduction

Reducing the consumption of sugar-sweetened beverages and drinking water is a justified and repeated recommendation found in many pediatric obesity prevention and treatment guidelines.1, 2, 3 Therefore, drinking water is an obvious alternative for the consumption of sweetened beverages for obesity prevention and treatment. Sugar-sweetened beverages might contribute an average of 224kcal per day (936kJ per day) to a child's energy intake, which could correspond to over 10% of the total daily energy intake.4 Replacing sugar-sweetened beverages with water could result in an average reduction of 235kcal per day (987kJ per day) in children and adolescents.5 In a recent study of a school-based intervention promoting water consumption for overweight prevention, a 31% reduction in the prevalence of overweight among study participants was noted.6

An intriguing mechanism by which water drinking may assist in reducing weight, is ‘water-induced thermogenesis’.7, 8 Related studies conducted in adults demonstrated that drinking water could significantly elevate the resting energy expenditure (REE). In the first study, drinking 500ml of water (temperature 22°C), elicited an increase in REE within 10min, reaching a maximum after 30–40min of 30% higher than baseline. This increase in REE was diminished when a beta-adrenoreceptor blocker was given, indicating that the sympathetic system was responsible for this rise in energy expenditure. In a second study, ingesting 500ml of water increased energy expenditure over the course of 60min after intake, again by a significant magnitude of 24% above baseline values, while administration of 500ml saline or 50ml water had no effect. This finding suggested that the REE-increasing effect is osmosensitive, and not related merely to gastric distension.

Surprisingly, a second research group was not able to replicate these findings.9 In this study, eight healthy normal-weight volunteers from both sexes drank 7.5ml kg−1 body weight (~518ml) of distilled water, 0.9% saline or a 7% sucrose solution (as a positive control). REE, measured from 30min before until 90min after the drinks, was not increased after drinking either distilled water or 0.9% saline. Drinking distilled water at 3°C caused a small increase in energy expenditure, of 4.5%, over 60min. This study introduced some uncertainty regarding the concept of ‘water-induced thermogenesis’. A possible explanation for the differences between these studies is differences in REE measurement techniques or other methodological issues. Additional study is therefore needed to establish the effect of water drinking on energy expenditure. Further, the extension of water-induced thermogenesis to the pediatric population has not been tested.

The aim of this study was to examine the effect of drinking cold water on the REE of overweight children.

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Methods

Participants were 21 overweight and obese children (11 boys, 10 girls; body mass index greater than or equal to85th percentile for age and sex1) aged 7–12 years (mean 9.9±1.4 years), from the pediatric obesity treatment program of a tertiary care center in Jerusalem, Israel. Exclusion criteria were the presence of any additional chronic medical condition, or the use of chronic medications. The study was approved by the Institutional Review Board of the Hadassah- Hebrew University Medical Center, and performed in accordance with the Declaration of Helsinki. Written informed consent was obtained from a parent following the child's agreement to participate.

Children came to the research facility in the morning, after at least 12h of physical inactivity and complete overnight fasting, during which no water drinking was allowed. Height and weight were measured for body mass index calculation and determination of the amount of water to be consumed. After an explanation of the methods, participants lay in bed and were covered with a ventilated hood connected to a portable metabolic cart10 (COSMED K4b2, Rome, Italy) for breath-by-breath respiratory gas exchange measurements. Baseline measurements lasted for 20min; the mean REE of the final 10 minutes was defined as the baseline REE.11 During REE measurements, the children watched a non-action movie of their choice, in order to reduce impatience and large movements. It was previously shown that television watching does not affect the REE of children;12, 13 this was also verified in our setting with a pilot study of three children, which lasted for 60min (data not shown). After determination of the baseline REE, children drank 10mlkg−1 body weight of commercially available natural mineral water (Mey Eden (‘Eden Springs’) Mineral Water Company (Bnei Brak, Israel). Total dissolved solids 240mgl−1, sodium concentration 1.4mmoll−1). Mineral water was preferred over tap water so as to control for solute concentrations. Water temperature was 4°C, measured by a thermometer with an accuracy of ±0.1°C (ME-03-HA-003, HANNA Instruments Inc., Woonsocket, RI, USA). Water drinking took 2–3min, after which the children resumed their lying position under the ventilated hood, and continued to watch the movie. The primary outcome measure was the REE after water drinking, which was measured for another 66min. In our pilot study of three children, rising and lying down again for 60min did not affect the REE (data not shown).

After termination of the metabolic measurements, body fat percentage was measured by bioimpedance analysis (Tanita BC-418 Segmental Body Composition Analyzer, Tanita Corp., Tokyo, Japan).

Statistical analysis

REE values after water drinking were analyzed using means of 3-minute segments, in order to reduce the number of measurements but maintain sensitivity. Repeated measures analysis of variance was used to compare the REE in each time point against baseline values, and a t-test was used to compare respiratory data between baseline and the time point of maximal REE. The net change in energy expenditure was calculated as the area under the curve of the mean REE during the study duration, by adding the sum of trapezoids. Spearman's correlation coefficient was used to assess the relationship between maximal REEs obtained after water drinking and the child's age, sex, height, weight, body mass index, fat mass percentage, lean body mass and amount of water consumed. P<0.05 was considered to be statistically significant. Statistical analysis was carried out using the PASW Statistics program, version 17.0.3 (SPSS Inc., Chicago, IL, USA).

The sample size was calculated based on previous studies7, 8 showing an REE elevation of 24–30%. Using a conservative expected elevation of 20% after water drinking, it was calculated that 19 children would be needed to demonstrate such a difference with a power of 80% and α=0.05.

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Results

Clinical characteristics of study participants are summarized in Table 1. All children were overweight, as per inclusion criteria. All drank the determined amount of water in the specified duration, and all completed the study.


Figure 1 shows the mean changes in REE after water drinking. We noticed a significant drop in REE immediately after water drinking, from 3.32±1.15kJ per min at baseline, to 2.56±0.66kJ per min at minute 3 (P=0.005), with a subsequent rise in energy expenditure. The REE was significantly higher than baseline values at 24min after water ingestion, 3.89±0.78kJ per min (P=0.021), and at most time points thereafter (Figure 1). The highest mean REE value was observed at 57min after water drinking, 4.16±1.43kJ per min (P=0.004). This corresponds to a maximal REE elevation of 25% from baseline. VO2 value at this time point was 26% higher than baseline (196±86ml per min vs 156±53ml per min, P<0.001) and VCO2 value at this time point was 20% higher (172±56ml per min vs 144±48ml per min, P=0.017). There was no significant change in the respiratory quotient between these two time points (0.88±0.8 vs 0.88±0.5, P=0.76). No significant difference was found in REE elevations between males and females (P=0.88). The net accumulated change in total energy expenditure from baseline to the end of measurement after 66min, using the mean REE of each time point, was 26kJ, with individual variability ranging from 13.4 to 84kJ.

Figure 1.
Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

REE following drinking of 10mlkg−1 of cold water (4°C). Water drinking at time point 0 is marked by a vertical arrow. Data points are mean values of the 3min before each time point, and error bars represent the standard error. Values that significantly differ from baseline are marked by an asterisk.

Full figure and legend (42K)

Table 2 presents the relationships between the various clinical characteristics of the participants, and both baseline and maximal REE values. REE was significantly correlated with age, height and weight, as well as with fat-free mass, with a much stronger relationship with the maximal REE than with baseline REE. body mass index correlated significantly only with the maximal REE value, while neither REE values correlated with fat percentage. Both baseline and maximal REE values also correlated with the volume of water consumed.


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Discussion

This study, conducted among 21 overweight and obese children from both sexes, demonstrated a 25% increase in REE following the drinking of 10mlkg−1 cold water (4°C). This increase was apparent from 24min after water drinking, and lasted for at least 66min. The unique effect of ‘water-induced thermogenesis’ is a negative caloric effect, that is, a net increase in energy expenditure, with no added energy intake. This effect is especially important for overweight and obese individuals seeking weight loss or maintenance.

An interesting finding was the large yet transient decrease in REE following the ingestion of cold water. A technical issue is unlikely, as this drop was not seen during baseline REE measurements (data not shown). We presume that this decrease occurred due to the rapid cooling of the upper gastrointestinal tract, which perhaps resulted in an adrenergic-related or other neural response. Although systemic cold exposure is well known to elevate the metabolic rate,14, 15 internal cold exposure by cold water drinking produces a different type of stimulus. The fact that previous studies did not report on this initial reduction in REE may raise the question regarding the generalizability of this phenomenon, for example, if it is dependent on age, overweight status, water volume or body/ambient temperature. The use of 10-min averaging of REE, as performed in previous studies, might cause this transient effect to be overlooked. Nevertheless, this REE reduction was short-term, and throughout most of the post-intervention observation period, REE was higher than baseline values. A previous study of cold water ingestion in adults (4°C, 900ml) showed a reduction in rectal temperature and heart rate during both rest and exercise, with improved exercise capacity.16 Together with our findings, these studies demonstrate that drinking cold water affects energy metabolism in both resting and exercise conditions. This effect can partially explain previous clinical observations in adults, that drinking water assists in weight loss.17, 18, 19

The timing, duration and relative magnitude of the REE increase seen in our study are very similar to those found previously.7, 8 In addition, we demonstrated that the ventilated hood system can be used to demonstrate water-induced thermogenesis in children, which until now was only shown by using a respiratory chamber and in adults. The mechanisms by which drinking cold water elevates the metabolic rate are incompletely understood. They have been suggested to involve the sympathetic nervous system,7 as well as gastric osmoreceptors.8 Gastric distention and gut hypo-osmolarity increase neural sympathetic activity, eliciting both a pressure response and the elevation of energy expenditure.20 Infusing a stomach with distilled water showed a twofold greater increase in blood pressure compared with isotonic saline, suggesting the role of hypo-osmolarity, possibly detected by hepatic osmoreceptors.20 In humans, distilled water, but not saline, increased heart rate and peripheral vascular resistance.21 This provided further evidence of an elevated sympathetic activity in response to the hypo-osmolar state. Recent research has identified molecular transduction mechanisms and channels involved in sensing hypo-osmotic signals and affecting blood pressure and metabolic rate.20 Water temperature could also have a role in REE elevation: in the study by Brown et al.,9 where no increase in REE after drinking distilled water or 0.9% saline was found, a small (4.5%) increase in energy expenditure was found after drinking distilled water at 3°C. Though water at 37°C also elevated the REE in a previous study,7 it was calculated that only 30–40% of the excess energy expenditure after drinking water at 22°C, was used for warming it to body temperature. The precise mechanism of the increased REE after water consumption remains to be identified.

The magnitude of REE elevation found in our participating children (+26kJ during 66min, mean 0.39kJ per min) is half of that seen in adults (+70kJ during 90min, mean 0.78kJ per min).7 This smaller absolute increase can be partially explained by the 30–50% lower mean baseline REE found in our children, as compared with findings from the adult studies.7, 8

Nevertheless, the relative increase, expressed as percentage of baseline, was similar. Hence, despite the low absolute REE in obese children compared with adults, water drinking was able to increase the REE by a similar proportion. Regarding the long-term effect of water drinking, it should be noted that the recommended amount for the average child at this age is 1800ml per day.22 Should the observed effect of a single drink occur repeatedly, then consuming the recommended daily amount of water would result in a mean energy expenditure of more than 34000kJ (over 8100kcal) per year; this could translate into an additional weight loss of about 1.2kg per year, just by adhering to general water drinking recommendations for children. In a study on older adults, drinking 500ml of water before each meal increased weight loss by +2kg over a 12-week period, explained only in part by a reduction in the energy intake of the meal;19 water-induced thermogenesis could have also assisted in the observed weight loss with pre-meal drinking. In another study in adults, an absolute increase in drinking water to greater than or equal to1l per day was associated with ~2kg weight loss over 12 months,18 the effect being significantly larger than drinking non-caloric beverages. This disparity can be explained by the previous observation of Boschmann et al.,8 that water-induced thermogenesis is osmosensitive, as drinking salt water did not elevate the REE while plain water did. Collectively, these studies provide evidence that water drinking may independently assist weight loss.

Regarding the associations between various clinical measures and REE (Table 2), it was expected that all measures of body size would correlate with REE, especially fat-free mass.23 These positive and strong associations reinforce the validity of our measurements, as fat-free mass is the main determinant of the REE. Interestingly, most correlations between body size indices and REE were stronger or became statistically significant with maximal compared with baseline REE values. A possible explanation for this is the effect of rehydration of muscle tissue by water ingestion following the overnight fasting state. The water content of muscle from obese adults was previously found to be 15% lower than that of adults of normal weight.24 Therefore, in addition to the osmosensitive and neural mechanisms of REE elevation suggested above, it is possible that the under-hydrated muscle tissue of the obese children became more metabolically active following its rehydration.

Our findings have two important clinical implications. Primarily, this study identified an additional benefit of water drinking by overweight children—increased energy expenditure. The high rate of overweight and obesity among children, reaching nearly 32% in the US,25 draws great attention even from the highest governmental levels.26 Obese children were found to have a lower REE per kg of fat-free mass as compared with normal-weight children,27 so any means to elevate their energy expenditure is welcome. Drinking water could therefore assist in weight reduction/maintenance in two complementary ways: by reducing energy intake as a substitute for sugar-sweetened beverages, and by increasing energy output through associated thermogenesis. Secondly, as current protocols for measuring the resting metabolic rate do not prohibit water drinking,28 the thermogenic effect of water should be taken into account. From our findings and those of the previous studies in adults,7, 8 it appears that drinking water within at least 90min before REE measurements should be disallowed.

This study has several limitations. Firstly, our baseline testing did not last as long as the post-drinking measurements. Having the children lie still for over 2h seemed unrealistic. Therefore, REE values after water drinking are compared with baseline values (as done in the previous studies in adults), and not to a corresponding time frame of no-drinking conditions. Nevertheless, we did not identify a spontaneous elevation of REE during 60min of rest in our pilot studies. In previous studies where REE was measured in obese children for 30min or more, no spontaneous elevation of REE was reported.23, 29, 30, 31 We therefore have no reason to believe that such an effect might have confounded our results. We also acknowledge that because we did not compare different types of water, or incorporate a broader range of subject characteristics, our findings may be limited to the specific temperature, volume and solute properties of the water used, as well as to overweight children from this specific age group. However, similar results shown in previous studies on adults with water at room temperature strongly suggest the generality of this phenomenon. Additional studies using water of different volumes and temperature, in the presence of beta-blockade, or in other pediatric populations, could help to elucidate the mechanism behind water-induced thermogenesis in children. The potential contribution of water drinking to metabolic balance could further help in the battle against the obesity epidemic, especially in children.

In conclusion, we found that drinking 10ml kg−1 of cold water resulted in an elevation of REE up to 25% from baseline values in overweight children. Consuming the recommended daily amount of water for children could result in an energy expenditure equivalent to an additional weight loss of about 1.2kg per year. Water-induced thermogenesis may therefore assist in weight loss and weight maintenance, in children as in adults.

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Conflict of interest

The ventilating hood used in this study was purchased using funding from Mey Eden (‘Eden Springs’) Mineral Water Company (Bnei Brak, Israel). Hadas Yariv was employed by Mey Eden (‘Eden Springs’) Mineral Water Company at the time of the study and this work was part of her Master's thesis. All other authors declare no conflict of interest.

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Acknowledgements

We wish to thank Dr Nira Koren-Morag for the statistical analysis.

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