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Impact of water intake on energy intake and weight status: a systematic review

Melissa C Daniels, Barry M Popkin
DOI: http://dx.doi.org/10.1111/j.1753-4887.2010.00311.x 505-521 First published online: 1 September 2010

Abstract

The effects of consuming water with meals rather than drinking no beverage or various other beverages remain under-studied. This systematic review of studies reported in the English-language literature was performed to compare the effects of drinking water and various beverage alternatives on energy intake and/or weight status. Relevant clinical trials, epidemiologic studies, and intervention studies were identified and findings across the literature were summarized. From the clinical trials, average differences were calculated in total energy intake at test meals (ΔTEI) for each of several beverage categories in comparison with water. The available literature for these comparisons is sparse and somewhat inconclusive. However, one of the most consistent sets of findings was related to adults drinking sugar-sweetened beverages (SSBs) versus water before a single meal. In these comparisons, total energy intakes were 7.8% higher (ΔTEI range, −7.5 to 18.9) when SSBs were consumed. Studies comparing non-nutritive sweeteners with water were also relatively consistent and found no impact on energy intake among adults (ΔTEI, −1.3; range, −9 to 13.8). Much less conclusive evidence was found in studies replacing water with milk and juice, with estimated increases in TEI of 14.9% (range, 10.9 to 23.9%). These findings from clinical trials, along with those from epidemiologic and intervention studies, suggest water has a potentially important role to play in reducing energy intake, and consequently in obesity prevention. A need for randomized-controlled trials to confirm this role exists.

  • energy intake
  • juice
  • milk
  • non-nutritive sweetened beverages
  • sugar-sweetened beverages
  • water
  • weight gain

INTRODUCTION

While there is a large and growing body of literature on the roles of a range of beverages on health,1,2 the role of water in supporting health remains under-studied. The importance of fluids for survival is well known. Without water, humans can survive for just 2–4 days. Water comprises about 60% of human body weight and is critical for life. Nevertheless, there are many unanswered questions about whether consuming water is superior to consuming other fluids or about the exact effect of replacing water with other fluids (e.g., various caloric and diet beverages) in the diet. Consensus is emerging that food intake is not reduced when caloric beverages are consumed35 and there is a need to further explore how energy intake and weight status are affected by the selection of various beverages compared to water in the diet. This review explores the hypotheses that 1) choosing alternatives to water at meals (i.e., no beverages, or various caloric and diet beverages) results in differences in energy intake, and 2) that choosing alternatives to water can have effects that extend beyond energy intake to affecting weight status.

A large number of studies and a number of reviews17 have examined the energy intake effects of adding sweetened caloric beverages (SCBs) to the diet, while few studies have examined the effects of fruit juices, milk, and other caloric beverages.811 While many of these studies considered water as an alternate beverage, the focus has been on the other fluids. Clearly, some of the meta-analyses and reviews have highlighted water as an important comparison group2 but most have used diet sweeteners or focused on dose-responses related to the consumption of more or less SSBs and other caloric beverages.

The bulk of the literature relating water to energy intake and weight (by contrasting water with no water or with other beverages before a meal) is comprised of short-term clinical studies of energy intake, usually occurring over a 2–5 h period. There are also a small number of cross-sectional and other epidemiological studies and a few interventions, which have often focused on energy intake.

LITERATURE SEARCH

A systematic review was conducted of English-language studies evaluating the impact of drinking water compared with no beverage or other beverages on energy intake and/or weight status. Studies were located in a cross-referencing manner, beginning with reviews and meta-analyses of beverages and energy intake116 as well as other beverage reports known to the authors. The reference lists of eligible publications were searched for further relevant studies. Studies citing eligible studies were also evaluated. When titles and subsequently abstracts mentioned beverages, the entire studies were reviewed for references to water. Reference and citation searches were performed using Web of Science and PubMed. Several short clinical trials, as well as a handful of longer term interventions and observational studies, were located.

Inclusion criteria

Eligible studies evaluated drinking water and one or more of the following comparison beverages: milk, fruit juice, and both diet and non-diet sweetened beverages (i.e., sodas and fruit drinks), or no beverage. These beverages were selected because they are commonly consumed and relevant to population health effects. The criteria and rationales used for excluding studies, along with a list of studies fully or partially excluded, are detailed in Table 1.

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Table 1

Criteria and rationale for exclusions, and list of excluded studies.

Exclusion criteriaRationale for exclusionStudies fully or partially excluded
Non-conventional beverages enriched with proteins and fatsLimited availability; limited consumptionWesterterp-Plantenga and Verwegen (1999)21; Wilson et al. (2002)22; Woodend and Anderson (2001)73
Comparison beverages with sugars and sugar mixtures other than sucrose, fructose, or glucoseLimited availability; limited consumptionBirch et al. (1989)43; Raynor and Epstein (2000)20; Shafer et al. (1987)48; Yeomans et al. (1999)74
Beverages with mixed caloric and non-caloric sweetenersUnable to be grouped cleanly with caloric and non-caloric beveragesWoodend and Anderson (2001)73; Akhavan and Anderson (2007)50; Birch et al. (1989)43; Guss et al. (1994)51; Spitzer and Rodin (1987)49
Comparisons with alcoholic beveragesPreviously shown to be additive to meal calories75; unclear relationship between alcohol calories and BMI appears to rest on absorption and metabolism issues unable to be addressedMattes (1996)12; Poppitt et al. (1996)76; Westerterp-Plantenga and Verwegen (1999)21; Yeomans et al. (1999)74; Yeomans and Phillips (2002)77
Studies presenting a food item that varied with the preloadMasking of beverage effectsCecil et al. (2005)78
Studies of athletes, studies in conjunction with exercise, and military studiesRepresentation of extreme circumstances not necessarily relevant to typical physiologic processesEngell (1988)79; Engell (1995)80; King et al. (1999)81

Quantitative and qualitative review

Clinical studies were typically single-blind, preload studies with a crossover design; most of them evaluated change in food energy intake at a single meal (usually lunch) served in excess, timed 0−60 min after a beverage preload. In four studies longer time frames (2 meals to 48 h) were used, and these studies are presented and discussed here. Total energy intake (TEI) consumed, including preload calories, was recorded or calculated for each study, with TEI measured as preload kcal + meal kcal. The change in total energy intake (ΔTEI), comparing water against no water or a beverage preload, was calculated for each study as ΔTEI = (TEIbev − TEIwater) ÷ TEIwater. ΔTEI was selected as the main comparative measure because it could be calculated and compared for both caloric and non-caloric beverages, and because total energy intake is directly linked to health effects. In several cases, ΔTEI had already been calculated by the authors, and those calculations were recorded and checked. Relevant statistical comparisons were also recorded. Weighted averages of ΔTEI across multiple studies were computed as ΔTEIwa = Σ(ΔTEI*N) ÷ Σ(N). All of the presented studies were included in weighted averages, regardless of significance. Without individual study data, confidence intervals and P values could not be computed for the weighted averages. Percent compensation (% Comp) has been commonly used elsewhere and is generally defined as the percent of preload calories (EIbev) by which the subsequent meal energy intake (MEI) changed. It was also calculated for all caloric beverages in this study (see appendices A and B) as %Comp = ([MEIbev − MEIwater] ÷ EIbev)*100. Where %Comp had already been calculated by the original authors, calculations were recorded and checked. When specific energy intake data were not listed, requests were sent by email to the first and last authors. Six studies were excluded because the authors could not be contacted or were unable to provide data.1722

Epidemiologic studies that directly measured the effect of drinking water on energy intake2326 or weight status2729 were very limited. Two school-based interventions30,31 and two clinical trials32,33 of sufficient length to evaluate the relationship between drinking water and weight loss were also located. These studies are summarized and discussed. Energy density studies, or the health impacts of varying the water content of foods and beverages, were not summarized. Total water studies that grouped drinking water intake with food and beverage water were also not summarized.

ANALYSIS OF FINDINGS

Clinical, preload, meal studies

A large number of short-term feeding trials compared water with either no beverage or a range of caloric beverages (as shown below). Nearly all used a crossover design. The present review examined, in the following order, the comparison of water with no water, milk and juices, various caloric sweeteners, and diet beverages. (The details of each study are presented in Tables S1 and S2 in the Supporting Information published online).

Does removing drinking water from meals affect energy intake?

If drinking water is removed from meals, is energy intake affected? Six clinical trials that addressed this question were compared in this review. Percent differences in energy intake are summarized in Figure 1 (see also Table S1 in the Supporting Information). These studies typically presented a reduction in calories when water was added to the diet. In this study we reversed presentation and made water the control to enable comparability with studies of other beverages versus water.

Figure 1

Difference in total energy intake when drinking water is removed from a meal. Total energy intake (TEI) includes combined kcal from preload and test meal. Differences presented are %ΔTEI calculated as 100*(TEI[w/no water]–TEI[w/water])/TEI(w/water). Weighted averages of ΔTEI across multiple studies were computed as ΔTEIwa = Σ(ΔTEI*N) ÷ Σ(N). All presented studies were included in weighted averages, regardless of significance. The studies cited typically presented a reduction in calories when water was added to the diet. In the present review we reversed presentation and made water the control to enable comparability with studies of other beverages versus water.

Among senior adults, meal energy intakes increased (ΔTEIwa = 8.7%) when premeal water was removed. Three recent studies by Davy et al.3335 contrasted no water with a water preload 30 min before a meal. Meal calories were significantly increased (8.6−14.8%) for both the non-obese35 and overweight/obese33,34 groups of seniors. Dennis et al.33 reported one non-significant observation (ΔTEI = 5.4%); however, it occurred after a 12-week diet intervention, which might have reduced differences at follow-up. No studies looked at time delays other than 30 min.

Among non-obese young-to-middle-age adults (four studies with nine comparisons) significant changes in energy intake did not coincide with the presence or absence of drinking water (ΔTEIwa = −3.1%). Five comparisons used a 30–60-min delay (Figure 1, footnote b), whereas four served water with or immediately before meals (Figure 1, footnote w). For all studies, regardless of timing, removing drinking water did not result in significant changes in meal energy intakes (ΔTEIwa = −5.0% water before meals; ΔTEIwa = −1.4% water with meals).

Does substituting water for caloric beverages before or with a meal reduce energy intake?

Water compared to milk and juice.  How does energy intake change if people drink water instead of juice or milk? Only two studies of adults36,37 and one study of preschool children38 addressed this question (Figure 2) (see also Table S2 in the Supporting Information). Delay times varied among the three studies, and beverages were served >2 h before the meal, with the meal, and just before the meal in each of the studies, respectively. In adult studies, ΔTEI was significant in five of the six comparisons (range 10.9−23.9) and weighted averages appeared similar for both juice (ΔTEIwa = 14.4%) and milk (ΔTEIwa = 15.2%). The preschool children reduced their meal intakes by 10% (P < 0.01) when drinking milk (juice not tested), but total calories still increased significantly (ΔTEI = 16.7%). Overall, ΔTEIwa was 14.9% for the three studies when individuals drank milk rather than water before or with a meal.

Figure 2

Difference in total energy intake when juice or milk displace water. Total energy intake (TEI) includes combined kcal from preload and test meal. Differences presented are %ΔTEI calculated as 100*(TEI[w/beverage]–TEI[w/water])/TEI(w/water). Weighted averages of ΔTEI across multiple studies were computed as ΔTEIwa = Σ(ΔTEI*N) ÷ Σ(N). All presented studies were included in weighted averages, regardless of significance.

Water compared to sugar-sweetened beverages.  Preload studies comparing water intake with SSBs have used various sugars and sugar mixtures. For comparison, studies were organized by the following sugar types: fructose and predominantly (≥65%) fructose beverages, glucose and predominantly glucose beverages, sucrose and high fructose corn syrup (HFCS: usually 55% fructose/45% glucose) beverages. The sucrose and HFCS category contained the largest number of studies, and is shown in Figure 3. Comparisons for glucose and fructose are described below.

Figure 3

Differences in total energy intake when HFCS or sucrose sweetened beverages displace water. Total energy intake (TEI) includes combined kcal from preload and test meal. Differences presented are %ΔTEI calculated as 100*(TEI[w/beverage]–TEI[w/water])/TEI(w/water). Weighted averages of ΔTEI across multiple studies were computed as ΔTEIwa = Σ(ΔTEI*N) ÷ Σ(N). All presented studies were included in weighted averages, regardless of significance.

Water compared to sucrose and high-fructose corn syrup beverages.  Among adults, drinking beverages sweetened with HFCS or sucrose generally raised energy intakes for a single meal compared to water. ΔTEI was positive for 12 of 15 comparisons (ΔTEIwa, 7.8%; range, −7.5 to 18.9) and half of these were significant. The four largest comparisons (N > 30) all reported statistically significant ΔTEI values of greater than 8%.3639

Four studies considered slightly longer time intervals of two or more meals1542 (see Figure 3, footnote L). All had unique design elements deviating somewhat from the typical preload paradigm (see Table S2 in the Supporting Information for details). Holt et al.42 and Lavin et al.40 considered beverages served with or interspersed with ad libitum high-fat/high-carbohydrate snack foods. One-day ΔTEI was not significant for either study (Holt et al.42ΔTEI, −7.9%; Lavin et al.40ΔTEI, 4.7%), nor were second-day intakes recorded by Lavin et al.40 (1.9%). Mattes et al.12 and Van Wymelbeke et al.41 compared intakes from two adjacent days. In both studies, total energy intake was significantly higher when meals were served with a sweetened beverage rather than with water (Mattes et al.12 cola ΔTEI, 7.2% P < 0.05; water ΔTEI, 1.7%, NS; Van Wymelbeke et al.41 fruit drink ΔTEI, 24.3%, P < 0.05). ΔTEIwa is not presented independently for these four studies due to the variation in study designs. For a single day of intake, combined with the single-meal studies above, overall ΔTEIwa was 8.2%.

In the only study of children, Birch et al.43 compared a sucrose fruit drink to plain water on snack intake in two experiments in preschoolers. The children consumed significantly fewer snack calories after a fruit drink compared to water regardless of delay (0, 30, and 60 min). Percent compensation was statistically equivalent to 100% in all cases (i.e., children reduced snack calories to perfectly offset their beverage calories). Therefore, TEI (ΔTEIwa = 3.1%, significance not tested) is likely to be similar for the two groups.

Time-course effects of semi-liquid preloads on subsequent intake have been shown previously.44 In response to liquid calories, time-course has been hypothesized to be of central importance,43 although only two studies evaluated multiple delay times.43,45 Therefore, adult single-meal HFCS and sucrose studies were evaluated to determine whether time delay from preload to meal had an influence on ΔTEI. When beverages were served with meals (6 comparisons, Figure 3, footnote w), most comparisons were clearly positive and significant (ΔTEIwa = 10.0%, four of six significant comparisons, with one [ΔTEI, 9.9] not tested). In contrast, when adult subjects drank a sucrose or HFCS beverage (versus water) 30 min or more before a meal (nine comparisons, see Figure 3, footnote b) ΔTEIs varied greatly (range, −7.5 to 18.9) but were not generally significant (ΔTEIwa = 5.5%, two of nine significant, with one [ΔTEI, 0.0] not tested). The comparison by Almiron-Roig et al.36 is a clear outlier as their preload was 135 min prior to the test meal (all other studies were between 30 and 80 min) (see Table S2 in the Supporting Information for listed delay times). When this study was excluded, ΔTEIwa dropped to 1.6% (range, −7.5 to 12.5) for the remaining eight studies, with only one study significant.

Water compared to glucose- and fructose-sweetened beverages.  To date, few studies have compared glucose- or fructose-sweetened beverages and water (see Table S2 in the Supporting Information). Four compared a glucose beverage with water4649 and one used an 80/20 glucose/fructose blend.50 All preloads were served at least 30 min before meals. Results were inconsistent and ranged widely (ΔTEIwa, 19.3%; range, −10.2% to 45.3%). Fructose beverages and water were compared five times in four studies,4651 and one study compared 20/80 and 35/65 glucose/fructose blends.50 All preloads were served at least 30 min before meals. ΔTEI was positive in five of seven cases (ΔTEIwa = 4.5%) but it was never significant, and the range of differences was again wide (−7.9% to 25.1%). Overall, the wide ranges and limited data for glucose and fructose made it difficult to discern any trends.

Does drinking water, compared to diet beverages, before or with a meal impact energy intake?

Studies containing diet beverages (Figure 4) typically used aspartame or beverages generally sweetened with aspartame (diet Coke and diet Pepsi); two comparisons with saccharin,47,52 and one with acesulfame-K47 were also included, as was a study that combined all three sweeteners in one beverage.41

Figure 4

Differences in total energy intake when diet beverages displace water. Total energy intake (TEI) includes combined kcal from preload and test meal. Differences presented are %ΔTEI calculated as 100*(TEI[w/beverage] − TEI[w/water])/TEI(w/water). Weighted averages of ΔTEI across multiple studies were computed as ΔTEIwa = Σ(ΔTEI*N) ÷ Σ(N). All presented studies were included in weighted averages, regardless of significance.

Ten adult studies gave a total of 19 comparisons. Sixteen comparisons reflected intakes at single meals. Differences were distributed on either side of zero (ΔTEI ranged from −7.4 to 6.1%; ΔTEIwa, −1.4%) and all differences were non-significant. Three longer studies (2+ meals previously discussed) also looked at diet beverages. Differences in TEI were non-significant, except in the one 2-day comparison. Lavin et al.40 reported a non-significant ΔTEI of 7.6% at the end of dinner when women drank diet lemonade, but by day 2 ΔTEI had increased to 13.8% and was significant (P < 0.05).

Birch et al.43 (see above description and Supporting Information) again provided the only study in children. Young children consumed significantly fewer snack calories when diet fruit drinks compared to water were served 30 min before the snack, but not with a longer delay (60 min) or no delay. This pattern was repeated in a second similar experiment. Across all comparisons, ΔTEIwa was −6.7%.

EPIDEMIOLOGICAL AND INTERVENTION STUDIES

Epidemiological population-level impacts of drinking water on energy intake

Four recent US studies (see Table 2) have explored the population-level benefits of drinking water on energy intake. Three used water data from the US National Health and Nutrition Examination Survey (NHANES) to conduct cross-sectional analyses. Two used fixed effects modeling, which uses individuals as their own controls and may reduce confounding by other variables.

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Table 2

Epidemiologic studies of water intake influencing energy intake.

First author (year)Funding (I,N,M)Sample characteristics (N gender, age, BMI)Study name location and timeStudy designDurationOutcomeRelated findings
Kant (2009)26N12,283 M and F, >20 years, mw; 4,112 M and F, >20 years, mw1999–2004 NHANES (US, nationally representative); 2005–2006 NHANESCross-sectional linear model estimating water intakes (plain, beverage, and total waters) as a function of energy intake and other dietary factors. Analysis was conducted separately for each data setNAPlain water intake was not significantly predicted by energy intake in either data setPlain water drinking was inversely related to consuming other beverages (−14.5 g beverage water/ 100 g plain water, P < 0.0001). Other beverages were positively associated with energy intake (44.1 g beverage water / 100 kcal, P < 0.0001)
Popkin (2005)23I4,755 M and F, >18 years, mw1999–2001 NHANESCross-sectional; cluster analysis evaluating food and energy intake patterns of water drinkers (87%) compared to those who did not drink waterNAWater consumers drank, on average, 1.5 L of water and consumed 194 fewer kcal per dayWater drinkers had healthier eating patterns including fewer kcal per day from sodas (−137), fruit drinks (−15), and fast foods (−62)
Stookey (2007)25I118 F, 25–50 years, 27–40 kg/m2Stanford A to Z weight-loss trials, California, ∼2005–2006Longitudinal; fixed-effects study comparing impact of various diet plans on weight loss and fat loss. Modeled changes in beverage intake and energy intake among baseline sugar-sweetened beverage (SSB) consumers.1 yearReplacing all SSBs with water, predicted mean energy intakes were decreased by 200 kcal/day over 12 months.§Replacing SSBs with non-caloric beverages, decreases were smaller; Replacing SSBs with nutritious caloric beverages did not reduce energy intake
Wang (2009)24N3,098 children, 2–19 years, mw2003–2004 NHANESCross-sectional; fixed-effects analysis of two 24-h recalls estimating the impact on total energy intake (TEI) of replacing sugar-sweetened beverages (SSBs) with healthier alternativesNAReplacing all SSBs with water could reduce child's TEI on average 235 kcal/day||Total energy intake increased >100 kcal per 8 oz (237 mL) serving of milk, juice, and soda, but did not increase with water or diet beverages
  • Plain water category excluded unflavored carbonated water. Model controlled for sex, age, race-ethnicity, body mass index, poverty-income ratio, years of education, smoking status, day of diet recall, leisure-time physical activity, average daily physical activity, any self-reported chronic disease, and survey wave.

  • Water category included tap or plain spring water. Unflavored carbonated water not mentioned.

  • § Model controlled for total beverage intake, non-caloric and nutritious caloric beverages, food composition, and energy expenditure.

  • || Model controlled for changes in other beverage consumption, day of the week, fast-food intake, and non-beverage intake. Using two time points, individuals were their own controls.

  • Abbreviations: I, industry; N, non-industry; M, mixed industry and non-industry; mw, mixed weight (normal, overweight, and obese); NHANES, US National Health and Nutrition Examination Survey.

Two of the NHANES studies and one of the fixed-effects studies focused on adults. Popkin et al.23 reported healthier dietary patterns including reduced soda intake and lower energy intakes among water drinkers in the 1999–2001 NHANES study. Kant et al.26 (1999–2006 NHANES) found that energy intake could not predict plain water intake, but was positively associated with consumption of other beverages. Stookey et al.,25 using a fixed-effects longitudinal model, evaluated women's weight and water intake changes over 12 months and found reduced energy intakes when women replaced other beverages with water. For each 1% reduction in beverages due to replacement with water, energy intakes were reduced by −9 kcal (SSBs), −8 kcal (milk, juice, or alcohol), and −3 kcal (non-caloric beverages). When all sweetened-caloric beverages were replaced with water, energy intakes were reduced by 200 kcal/day. No benefit was predicted if sweetened caloric beverages were replaced by other caloric beverages.

Wang et al.24 considered water intake in children (ages 2–19 years) using a fixed-effects model over 2 days of intake. For each 8 oz serving of a range of beverages, energy intakes increased commensurate with beverage calories, i.e., no change (water and diet beverages) P > 0.20; 106 kcal (SSB's), 169 kcal (whole milk), 145 kcal (reduced-fat milk) and 123 kcal (juice); P < 0.001 for all caloric beverages. Overall, the authors estimated a reduction of 235 kcal/day if all SSBs were replaced with water.

Epidemiologic studies of water and weight status

Epidemiologic studies exploring the relationship between drinking water and weight status (see Table 3) were limited to two generalized linear model (GLM) analyses that controlled for body size, and one more complex mixed models analysis, with individuals serving as their own controls).

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Table 3

Intervention and epidemiologic studies of water intake influencing weight status.

First author (year)Funding (I,N,M)Sample characteristics (N gender, age, BMI)Study name location and timeStudy designDurationOutcomeRelated findings
Epidemologic studies
Kant (2009)26See Table 2 above. Unadjusted plain water intakes did not vary by weight status in 2005–2006 NHANES; plain water intakes were higher among those with higher BMI in 1999–2004 NHANES analysis
Johnson (2007)27NRound 1: 521 kids, 5.2 ± 0.6 years, 16.0 ± 1.4; round 2: 682 kids, 7.4 ± 0.1 years, 16.2 ± 2.1; round 3: 692 kids, 9.8 ± 0.2 years, 17.7 ± 2.8ALSPAC; England; ∼1997–2001Longitudinal study; GLM model of fat mass at age 9 years as a function of beverage consumption at ages 5 and 7 years. Water category included flavored water4 yearsWater intake at age 5 and 7 years was not significantly associated with change in fat mass by age 9 years in crude or adjusted modelsSSB intake did not predict fat mass by 9 years. Higher milk intake significantly predicted lower fat mass (at 5 years, −0.51 kg/serving P < 0.01; at 7 years −0.35 kg/serving P < 0.01)
Phelan (2009)28M131 M and F, 49.9 ± 13.2 years, 21.3 kg/m2 (always NW); 172 M and F, 48.2 ± 11.6, 22.0 kg/m2 (WLM)Sample from National Weight Control Registry (US). Study dates not specifiedCross-sectional study using three 24 h recalls. Simple GLM comparison of food and beverage intakes of normal-weight individuals with weight-loss maintainersNAWater was main beverage for both groups; WLM drank more daily servings of water (4.7 versus 3.5; P = 0.002)WLM also had larger serving sizes for water (P = 0.0001) and marginally greater % of overall beverage intake from water (P = 0.06)
Stookey (2008)29M173 F, 25–50 years, 27–40 kg/m2Stanford A to Z, California, ∼2005–2006Longitudinal study over 12 months; used nested mixed models to estimate effects of absolute and relative changes in water intake on weight gain. Participants from four diet groups1 yearIndividuals drinking >1 L water/day lost, on average, 2.3 kg more weight and 2.3 cm WC than those drinking <1 L/dayReplacing 1% of SSBs with water significantly reduced weight (0.3 kg), WC (0.03 cm) and body fat (0.03%)
Intervention studies
Davy (2008)32 (abstract only)NL29 M and F, 62 ± 1 years, 33 ± 1 kg/m2Virginia Tech; 2006–2008Clinical intervention study comparing drinking water before meals versus control; groups received identical weight-loss intervention6 monthsMean weightt loss: −11 ± 2 kg (water), −7 ± 1 kg (control). P = 0.09 (still in progress at time of writing: 20 of 29 had completed 6 months)Rapid weight loss was more common and more often sustained among premeal water drinkers
Dennis (2010)33N18 M and 30 F, 55–75 years, 25–40 kg/m2Virginia Tech; July 2006–September 2008Clinical intervention study looking at the difference in weight loss when a low-calorie diet is coupled with premeal water (500 mL) or no water instructions12 weeksSignificant weight loss in both groups; greater weight-loss rate in water group. Water consumers had significantly reduced fat mass (P = 0.01)Differences in %wt, % body fat, BMI, waist circumference, blood pressure, and blood lipids were not significant
James (2004)30M324 boys and 320 girls, 7–11 years, MWCHOPPS; Southwest England; August 2001–October 2002Primary school classroom level intervention to reduce carbonated drinks and increase water drinking. Various educational methods used: didactics, slogans, games, contests, music.1 school yearPercent overweight§ increased significantly for controls (+7.5%) but not intervention (−0.2%) group.Increases in water intake were similar for both groups, while SSBs decreased with intervention. Substantial underreporting.
Muckelbauer (2009)31N2,950 kids, 8.3 ± 0.7 years, MWGermany; August 2006–June 2007Primary school school-level intervention to promote drinking water and reduce overweight. Intervention was both educational (didactic) and environmental (filtered fountains, water bottles, daily filling process)1 school yearIntervention group water intake was 220 mL/day greater; Adjusted risk of overweight was 31% lower for intervention group. [OR = 0.69 (95% CI 0.06, 1.91)]Intervention had no effect on soft drink and juice consumption
  • Model was adjusted for sex, height at 9 y, child's body mass index at baseline, television watching, maternal education, paternal class, maternal body mass index, paternal body mass index, misreporting of energy intake (energy intake per estimated energy requirement), dietary energy density, percentage of energy intake from fat, and fiber density.

  • Model was adjusted for age, race/ethnicity, baseline status, and diet treatment group, energy expenditure, energy intake from food, and food macronutrient and water composition.

  • § Defined as mean percentage >91st centile.

  • Abbreviations: I, industry; GLM, generalized linear models; N, non-industry; M, mixed industry and non-industry; MW, mixed weight (normal, overweight, and obese); NW, normal weight; WLM, weight loss maintainers; WC, waist circumference; SSBs, sugar-sweetened beverages; CHOPPS, Christchurch Obesity Prevention Projects in Schools; ALSPAC, Avon Longitudinal Study of Parents and Children; CHNS, Chinese Health and Nutrition Survey.

Two studies focused on adults. Phelan et al.28 used simple GLM models to compare diets of weight-loss maintainers and normal-weight controls from the national weight control registry. Weight-loss maintainers drank more servings of water (4.7 versus 3.5, P = 0.002), with larger portions (2.03 servings versus 1.35 servings, P = 0.0001). Stookey et al.,29 using nested mixed models, found greater losses in weight (2.3 kg) and waist circumference (2.3 cm) when individuals drank >1 L water/day over 12 months. Replacing 1% of sweetened beverage intake with water also significantly reduced weight (0.03 kg, P < 0.05), waist circumference (0.03 cm, P < 0.05), and body fat (0.02%, P < 0.05).

In the only study of children, Johnson et al.27 compared fat mass (at age 9 years) with previous beverage data (5- and 7-year). Neither earlier water nor SSB intake predicted fat mass by the age of 9 years. However, authors admitted low energy intakes (∼30% implausible) with under-reporting substantial among overweight children. Low reported consumption of SSBs in this sample (∼150–300 g/d or 5–10 oz/d) and even lower water intakes (∼100–150 g/d or ∼3.5–5 oz/d) are questionable.

Intervention studies of water and weight status

Only four studies exploring water drinking as a weight-loss intervention were located (see Table 3). Two were clinical studies of older adults based at Virginia Tech University in the United States; two were school-based interventions in English and German primary schools.

The two clinical studies performed weight-loss interventions on older adults and seniors. In addition to weight-loss training, a portion of the sample was assigned to drink water before meals. Dennis et al.33 observed a significant decrease in total fat mass at 12 weeks among water drinkers (−5.4 ± 0.6 kg versus −3.3 ± 0.5 kg, P = 0.01), although reductions were not significant when expressed as a percentage of initial weight, or percent body fat. BMI and waist circumference were not significantly different. Davy et al.,32 reporting preliminary results of a 6-month intervention, observed a tendency to greater weight loss (−11 kg versus −7 kg, P = 0.09). Both studies reported more rapid weight loss among premeal water drinkers.

James et al.30 delivered an educational intervention to 15 classes in six schools (14 control classrooms had no intervention) to reduce consumption of carbonated beverages and to increase water drinking. Four 1-hour classes (by one investigator) presented a variety of instruction, demonstrations, music, contests, and games. At one year following the intervention, children completed two 3-day drink diaries. Intervention classes reported lower carbonated beverage intake (difference = 0.7 glasses/3 days; range, 0.1−1.3]) and children were weight stable (change in percent overweight −0.2% versus +7.5% controls). Reported water intakes increased similarly for both groups; however, the authors reported a low return rate for the two diaries (55% initial, 56% final, 36% both).

Mucklebauer et al.31 instituted both educational and environmental interventions to increase water intake in 17 German schools (15 control schools had no intervention). Teachers presented four empirically developed lessons about the body's water needs and the water cycle. Special filtered drinking fountains were installed, water bottles were distributed, and teachers were encouraged to organize filling of water bottles each morning. After one year, children completed 24-h beverage intake recalls in class. Interventions in schools led to higher water intakes (1.1 glasses/day, P < 0.001), and lower adjusted risk of overweight (OR, 0.69; 95% CI, 0.48–0.98).

CONCLUSION

This review clarifies what is known about the effects of drinking water on energy intake and weight status, and highlights critical gaps in the literature. The available evidence does not support that removing drinking water from a meal significantly changes TEI, although a small increase in TEI was seen in older adults. In contrast, for adults, the review finds reasonable agreement among a number of single-meal studies that replacing water with SSBs will increase energy intake (7.8% ΔTEIwa,; range, −7.5 to 18.9). There were far fewer studies replacing water with juice and milk, but the weighted average showed a sizeable increase in total energy intake (15% ΔTEIwa; range, 10.9–19.7). The literature on comparing water with artificially sweetened beverages found a negligible statistically insignificant reduction in energy intake (−1.4% ΔTEIwa; range, −9.0 to 13.8%).

The following key gaps in the caloric beverage literature were identified. Studies comparing water with caloric beverages in children were almost non-existent. The single existing study in children found no difference in TEI when children consumed SSBs (3.1%, NS), which contrasts sharply with the increase reported when children drank milk (16.7%). The largest set of studies currently available relates SSBs and water intakes at single-meals in adults. Results from studies of beverages sweetened with HFCS and sucrose were much more conclusive, with a 7.8% increase in total energy and many studies finding statistically significant results. Great heterogeneity was found in adult studies and findings based on sweetener type, i.e., there was a range of studies on beverages sweetened with HFCS and sucrose and minimal work on beverages sweetened with pure fructose or glucose. Very few studies considered the energy effects of water versus other beverages at more than one meal, and these had increasingly divergent study designs and findings. Clearly, all of this literature is very short-term and the critical gap is longer-term randomized controlled trials.

The diet sweetener literature is not very conclusive. Elsewhere, we recently reviewed what is known about consumption patterns and biological pathways by which these sweeteners might affect behavior.53 Diet beverages have been compared frequently to various solid and liquid preloads,13 but less commonly with plain water. In this review, artificially sweetened beverages clearly did not increase energy intake at the next meal compared to plain water. Again, very few studies have considered effects longer than one meal.

Dietary regulation may differ by age; unfortunately, most studies explored regulation only in adults and very few contrasted subjects of different ages. The study of children by Birch et al.43 found this group had a greater ability to compensate for caloric intake through beverages than the subjects in the collection of adult studies (Figure 3). The studies of seniors by Davy et al. (Figure 1) found a tendency for caloric intake to be reduced when water was consumed before a meal, while studies of younger adults found no clear effect. With just a few studies on children, it is almost impossible to provide any sense about dietary regulation as it relates to beverages and water in children. Research is needed to explore age effects, and clarify age brackets in which energy regulation may vary.

This review suggests delay time may impact the effect of caloric beverages on energy intake. When adult single-meal SSB studies were stratified by delay time, ΔTEIwa was 1.6% with all but one study being non-significant if beverages were served 30–80 min before the meal. ΔTEIwa was 10.0% and generally significant if served with a meal. Juice and milk studies had a larger ΔTEIwa (14.9%), but all served beverages with or long before meals (2+h), which appeared to increase TEI relative to short delays in SSB studies. As hypothesized by Birch et al.43 20 years ago, time course may indeed be “of central importance” in modulating the effect of liquid calories on energy intake and appears worthy of attention in future studies.

The epidemiologic literature exploring the effects of water on energy intake and weight status is also strikingly sparse and this, along with variations in study designs, made drawing broad conclusions difficult; we must consequently be cautious in our interpretation. In general, studies supported an inverse relationship between drinking water and energy intake when compared with other beverages,2325 with both fixed-effects studies estimating a reduction of 200+ kcal per day if all sweetened caloric beverages were replaced with water.24,25 The adult studies by Phelan et al.28 and Stookey et al.29 looking at weight status supported an inverse relationship with water drinking, while the study by Johnson et al.27 did not, but it was focused on children and suffered from substantial underreporting. Of the epidemiologic studies, the two Stookey papers were most noteworthy, both for their careful modeling with fixed-effects and because they were secondary analyses of intervention data (rather than observational). By following women on a range of diet plans that shifted water intake, the studies found significant differences in energy, weight, and percent body fat among those drinking greater amounts of water.54,55

While further epidemiologic studies would be desirable, there are challenges to this literature. With self-reported dietary data (used in all of the above studies) underreporting is common and is thought to occur similarly with both water and energy intakes.56 Since underreporting for water and energy intakes is thought to be balanced, whereas dietary underreporting is known to differ by weight, the studies of weight status naturally require a more cautious interpretation. Another notable challenge for epidemiologic studies is isolating the effects of water drinking. The studies by Popkin et al.23 and Kant et al.26 were in agreement with other studies57 that water intakes are strongly tied to other dietary patterns. Both studies also demonstrate the known coexistence between dietary pattern differences and sociodemographic differences. Since the two are so tightly linked, removing sociodemographic variation to control confounding also limits diet pattern variation, and may obscure related water benefits. Does drinking water support other more healthful dietary patterns? Or does it merely coexist with them? Clearly, further studies are needed to answer this question.

Few intervention studies rigorously examined the role of water education or using water to replace other beverages consumed at the school. The most potentially intriguing result was the German intervention in 32 schools. This year-long German intervention promoted water both by educating about the importance of water and making filtered water readily available to children. The intervention schools increased water intake by 220 mL/d with a significant 31% reduction in the risk of overweight.31

This review suggests plausible benefits of increasing water intake and invites further investigation. Reduced energy intakes are expected when water replaces other caloric beverages at a single meal, but this may not translate into long-term weight changes. For example, drinking milk and SSBs both increased single-meal energy intakes substantially compared to water, but Stookey et al.29 and Johnson et al.27 both found that milk was much less likely than SSBs to promote weight gain. Longer-term randomized controlled trials of water drinking and weight status are needed to better understand these relationships.

The limitations of this review really relate to the lack of randomized controlled trials and more studies that go beyond short-term feeding trials to week-long, month-long, and longer studies. Most of the studies in this review looked at energy intakes at a single meal following a beverage preload, and very few examined the effects of water drinking on more than a day or two and certainly did not not determine 3–6-month or even year-long changes in energy intake or weight. It is critical to understand that future designs should include some randomized controlled trials of the effects of replacing SSBs, other caloric beverages, and diet beverages with water. Since beverage intake patterns are linked with sociodemographic characteristics, studies of this type will be important for fully understanding the future program and policy agenda most clearly.

Along with the great deal of further research needed to define the relationship of water drinking and weight status, research is needed to understand the driving mechanisms supporting these relationships. Rather than assuming energy intake is the only way water intake may affect weight, some early studies support the presence of alternate metabolic pathways. For example, Boschmann showed increased thermogenesis and caloric expenditure within 60 min of drinking water.58,59 Others have suggested that reduced serum osmolality from drinking water may improve cell efficiency and increase fat metabolism.60,61 Unfortunately, the existing research investigating these theories is presently very limited and, at best, speculative; much more work is consequently needed.

Obesity is clearly linked to a host of health problems, and this connection alone supports the promotion of water drinking. Beyond its role in reducing energy intake, however, the unique benefits of water drinking are less well defined. Clearly, maintaining adequate hydration status has important health implications, as discussed at length in a companion paper.62 Most beverages can support hydration, but water is unique in its capacity to do this without also adding sugars or many other compounds to the diet. Unfortunately, little research exists exploring the broader health implications of water intake versus other beverages; however, recent studies linking SSBs to increased rates of diabetes63 and heart disease64 through pathways independent of BMI begin to imply even further benefits of water drinking.6568 The sparse literature on this topic was not reviewed herein as there is currently little consensus on any of these alternate pathways.

Very recently, the American Heart Association published a statement that raised significant questions about the high level of added sugar in the US diet and suggested that American women should consume no more than 100 calories per day, while American men should consume no more than 150 calories per day from added sugars.69 Given the very high intake of calories from beverages in the US diet, following this recommendation would necessitate major shifts in beverage intake patterns in the United States.70,71

Overall, this review suggests promising results for promoting water as a replacement beverage. As shown elsewhere, the proportion of water in the average diet has diminished over time as individuals have shifted consumption patterns to a range of beverages that contain either one or many of the following: sugar, caffeine, natural and artificial flavorings, nonnutritive sweeteners, and carbonation. The beverage revolution in the post World War II period truly shifted drinking patterns and possibly even total fluid intake.572 The question that remains to be answered completely is “Will there be a benefit to shifting back to water more than to other beverage options that reduce or eliminate calories from our diet?” Longer-term randomized controlled trials and more interventions with strong compliance-monitoring designs are needed to fully understand the benefits of drinking water as a replacement for a range of caloric and non-nutritive beverages.

Funding

Funding was provided by the Nestlé Waters, Issy-les-Moulineaux, France, and NIH R01-CA109831 and R01-CA121152.

Declaration of interest

None of the authors has any relevant interests to declare.

Acknowledgments

The authors wish to thank Ms. Frances L. Dancy for administrative assistance, Mr. Tom Swasey for graphics support, Doctors Irwin Rosenberg and Kris D'Anci (Tufts University) and Florence Constant (Nestle's Water Research) for advice and references.

REFERENCES

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