1. Introduction
Beverages are significant contributors to the daily diets of US adults and have been associated with health through a number of different pathways [
1]. Sugar-sweetened beverages (SSB), including soda and sweetened fruit drinks in particular, have remained at the forefront of obesity-related policy debates due to their contribution to excess energy intake and the observation that liquid calories (e.g., beverages) may [
2,
3,
4] or may not [
5,
6,
7] be as satiating as calories in solid form (e.g., food). Regular SSB consumption has been positively associated with increased body weight and risk of obesity [
8,
9,
10,
11,
12,
13], diabetes [
9,
14,
15,
16], cardiovascular disease [
10], and adverse dietary intake patterns [
10,
17]. While there is increasingly consistent evidence suggesting that total SSB consumption has been declining over the past 10–15 years [
18,
19], current consumption levels among many racial/ethnic, age, and income groups nationally (and internationally [
20]) remain higher than recommended [
19]. For example, while the prevalence of soda consumption among US adolescents decreased between 1999 and 2010, the prevalence of energy drink consumption tripled over that same time period [
19].
Maintaining adequate hydration, specifically through water consumption, is associated with a number of beneficial health outcomes including maintaining peak physical and cognitive performance [
21], weight management [
22] and weight gain prevention [
23], and improving metabolic rate [
24]. Though there is not a Recommended Daily Allowance for total water intake, the Institute of Medicine’s Food and Nutrition Board suggested a Daily Recommended Intake for adult males and non-pregnant, non-lactating females over 19 years of 3.7 L/day and 2.7 L/day, respectively. Although water intake remains below recommended levels among most segments of the population [
24,
25], bottled water is poised to overtake soda as the top selling beverage (by volume) [
26,
27], and powerful new marketing campaigns [
28] are hoping to change the way Americans think about water, bottled and tap [
29].
Among the top recommendations put forth in the 2015 Dietary Guidelines for Americans is to shift to healthier food and beverage choices [
30], specifically that Americans should “shift to reduce added sugar consumption to less than 10 percent of calories per day” [
30]. The guidelines additionally state that when choosing beverages “calorie and nutrient contribution to the diet should be considered” and that “calorie-free beverages—especially water—should be favored” [
30]. Making individual beverage choice changes can be a challenge because recommendations are not put into the broader context of overall beverage and dietary intake patterns. The Healthy Beverage Index (HBI) [
31] was designed to overcome that challenge by providing a system for evaluating overall beverage quality and comparing that intake against standards set forth by the Dietary Guidelines for Americans and the Beverage Guidance Panel [
32]. Furthermore, preliminary studies indicate that higher HBI scores are positively associated with cardiovascular health [
31,
33] and may, therefore, prove a useful tool for evaluating the beneficial impact that changes in beverage consumption patterns might have on health.
The purpose of the present study was to evaluate the potential impact of replacing one serving of SSB with water on HBI score and overweight prevalence.
4. Discussion
This present study confirmed previous reports that a considerable portion of adults are regular consumers of SSB and that those who frequently consume SSB have higher levels of total energy intake as well as energy from beverages. Individuals who consumed a higher number of servings of SSB also had significantly lower HBI scores, indicating that they were further from meeting beverage recommendations compared to those who were SSB non-consumers. In the present study we also report that replacing one serving of SSB with one serving of water significantly improved HBI scores, lowered percent of energy from beverages across intake groups and, in the lowest intake group (1 serving SSB) allowed them to meet the recommendation of consuming <14% of total energy from beverages. Lastly, our findings provide further evidence that water replacement may be an effective strategy for adults concerned about excessive weight. The energy reduction associated with water replacement we predict would significantly lower the proportion of adults classified as obese from 35% down to 32% of the population.
Similar results have been previously reported. A recently published study of more than 18,000 adults using US-based nationally representative dietary intake surveys predicted that a 1 percentage point increase in the proportion of daily plain water was associated with a reduction of roughly 8.5 kcal/day [
25]. This finding has been confirmed in experimental and epidemiological studies, where pre-meal water consumption has been documented to reduce meal energy intake in various groups of individuals, including those who are overweight and obese and among older adults [
41,
42,
43]. Given these previously estimated energy savings (68 kcal savings with an 8 ounce replacement of water for SSB [
25]), and the fact that roughly 30% of US adults drink one or more servings of SSB/day [
44], swapping water for SSB could reduce an estimated 3.9 billion calories from US adult diets daily. Using the observed prevalence of adults consuming at least one SSB serving/day in this study (41.4%), this saving could be as high as 5.8 billion calories saved from American adult diets daily.
Evidence of the impact of SSB reduction on body weight is unequivocal. Using nationally representative data from the UK, Ma et al. [
45] report that an estimated 40% reduction in free sugars added to SSB over five years would result in an estimated 1.2 kg body weight reduction and a 1% point decrease in the prevalence of overweight and 2.1% point decrease in the prevalence of obesity among adults [
45]. In the US, each one cup per day increment of water intake was inversely associated with weight gain over a 4 year period [
23] and a 2013 meta-analysis of RCTs provide fairly convincing evidence that decreasing SSB consumption will decrease the risk of obesity and obesity related diseases such as Type 2 diabetes [
8]. Daniels and Popkin additionally state that findings from clinical trials and epidemiologic and intervention studies suggest water has a potentially important role to play in reducing energy intake, and consequently in obesity prevention [
46]. These findings have been replicated in non-US settings as well [
16,
47,
48]. However, Hernandez-Cordero et al. [
49] found there was no effect of the intervention on triglyceride concentration or on any of the studied outcomes (including weight and waist circumference) in a group of overweight and obese Mexican women [
50].
Nonnutritive, or diet, beverages as a replacement for SSB (instead of water) have also been suggested as a means to promote weight loss or encourage weight maintenance, but the findings from these studies are also equivocal. Recently published results from a 1-year RCT evaluating the effects of water compared to low-calorie sweetener (LCS) beverages on body weight in subjects participating in a commercially available weight loss treatment program reported greater 1-year weight loss maintenance among those in the LCS compared to water groups (6.21 kg vs. 2.75 kg respectively) [
51]. Others report no difference in weight loss (after 6 months) in the Low-Calorie Beverage compared to Water intervention group [
52]. However, they did find that participants in the Water arm of the intervention significantly increased their consumption of fruits and vegetables [
53] and had greater reductions in other important markers of health including fasting glucose and improved hydration [
53]. Earlier research has shown that dietary and beverage patterns are associated with one another, suggesting that choosing water over diet beverages, as a replacement for SSB, may be associated with other healthy dietary choices [
54,
55,
56].
The studies from which our weight-loss estimates were drawn were based on weight loss observed in randomized controlled trials, which lasted 6 (−0.40 kg weight loss) and 8 months (−1.99 kg weight loss) in a free-living population. In the context of evaluating potential weight loss, this is a meaningful distinction because RCTs that use a controlled feeding methodology may have limited generalizability to a free-living population [
57]. Our study did not specifically examine or model the potential compensatory changes in dietary components (including foods and beverages) or in other behaviors like changes in physical activity, except to the extent that these compensatory changes were observed in the free-living population participating in the original weight loss studies themselves [
39].
Although trends indicate some decline in intake of sugar sweetened beverages, most Americans are still consuming too many calories from beverages, and from sugar-sweetened beverages specifically. There is ample evidence to suggest that this overconsumption is a contributing factor to excessive weight gain and that options for reducing energy intake, especially the excess energy from beverages, can help limit this excessive weight gain and might even contribute to weight maintenance or weight loss. Results from our study provide further evidence that replacing SSB with water is one potential strategy to achieve these energy reductions and which could benefit adults in the US. Evaluating the impact of water replacement on diet and weight in children and the development of the HBI for a pediatric population are important directions for future research on this topic.