Introduction

Globally, the prevalence of overweight and obesity in adults doubled between 1980 and 2008 (1).Worldwide, 2.8 million people die each year (5% of global deaths) as a result of being overweight or obese (1). The need to address this mounting epidemic is urgent as the numbers are growing rapidly in virtually all countries, including low- and middle-income countries.

The challenges from an increasingly global “obesogenic environment” that promotes high-energy dietary intakes and sedentary activity mean that addressing environmental and public health factors are increasingly seen as essential (2,3). Heavy marketing of sugar-sweetened beverages (4) contributes to the obesogenic environment and has led to a steady increase in global consumption of sugar-sweetened beverages (5). Of particular concern is the rise in consumption in many low- and middle-income populations, as well as amongst lower-socio-economic children, adolescents and adults in affluent societies (4,6). Sugar-sweetened beverages, now the primary source of added sugars in the American diet and 10% of total dietary energy in Mexican diets (7), include energy-containing sweeteners such as sucrose, high-fructose corn syrup, or fruit juice concentrate, all of which have essentially similar metabolic effects (8). Sugar-sweetened beverages may lead to weight gain through their high sugar content (140–150 calories and 35.0–37.5 g sugar per average 12 oz serving), low satiety, and an incomplete compensatory reduction in energy intake at subsequent meals after the intake of liquid calories (9).

Numerous systematic reviews of the literature confirm the link between increased consumption of free sugars, particularly in the form of sugar-sweetened beverages and unhealthy weight gain in both children and adults (5, 9–14). This commentary will focus on results from one of the most recent systematic reviews evaluating sugar-sweetened beverage consumption and unhealthy weight gain in adults (13).

Methodology summary

The systematic review and meta-analysis of Malik et al. (13) used standard methods for conducting and reporting meta-analyses with relevant articles identified by searching PubMed, EMBASE and the Cochrane Library, using various terms for sugar-sweetened beverages and for body weight, related cardio-metabolic outcomes (e.g. diabetes mellitus, insulin resistance, cardiovascular diseases, hypertension), and various study design/epidemiological methods, but focused on outcomes related to body weight. Potential sources of heterogeneity, including adjustment for total energy, duration, age, dietary assessment, method, sample size, and baseline weight status, were explored by using univariate meta-regressions and stratified analyses. Study-level risk of bias was assessed. Thirty-two original articles (twelve conducted in adults) were included in their meta-analysis, with excluded studies evaluated qualitatively. All studies were adjusted for additional diet and lifestyle factors but none for total energy intake.

Evidence summary

Prospective cohort studies

Seven studies consisting of 170,141 adult men and women were included in the analysis of sugar-sweetened beverage consumption and change in body weight over one year. An increase of one serving per day of sugar-sweetened beverages was associated with an additional weight gain of 0.22 kg over one year (95% CI: 0.09 to 0.34) using the random-effects model. The estimate from the fixed effects model was also significant but not as strong (mean difference (MD) 0.12 kg [95%CI: 0.10 to 0.14]). When the analysis was stratified by baseline weight status, there was greater, although non-significant, weight gain associated with increased sugar-sweetened beverage consumption in the studies conducted in overweight populations (MD 1.22 kg [95%CI: –0.23 to 2.68]) compared with those conducted in populations that were not overweight (MD 0.15 kg [95%CI: 0.06 to 0.24]).

Trials

Five trials, consisting of six comparisons of 292 adult men and women, were included in the analysis. The authors found a significant association between increased consumption of sugar-sweetened beverages and weight gain (weighted mean difference (WMD) 0.85 kg [95% CI: 0.50 to 1.20]) using the random effects model. The estimate obtained from the fixed-effects model was identical. All studies observed significantly greater weight gain or trends toward greater weight gain with increased sugar-sweetened beverage consumption, and there was no evidence of heterogeneity. When the analysis was stratified by baseline weight status, the association between sugar-sweetened beverage consumption and weight gain was greater in the studies conducted in nonoverweight populations (WMD 0.89 kg [95%CI: 0.52 to 1.26]) compared with those conducted in overweight populations (WMD 0.47 kg [95%CI: –0.70 to 1.63]).

Qualitative evaluation of studies not included in the analysis

The majority (four of six) of the cohort studies in adults that were excluded (as a result of difficulty in deriving suitable units for pooling) found positive associations between sugar-sweetened beverage consumption and body weight in either primary analysis or subgroup findings, whereas two studies did not find significant associations. Two large cohort studies, which were excluded because they were conducted in previously-documented duplicate populations, found significant associations between increased sugar-sweetened beverage consumption and weight gain (15,16).

Discussion

Findings from the systematic review and meta-analyses by Malik et al. showed an overall positive association between consumption of sugar-sweetened beverages and weight gain in adults. Based on results from analysis of prospective cohort studies, the authors concluded that an increase in consumption of sugar-sweetened beverages by one serving per day was associated with additional weight gain in adults of 0.12 to 0.22 kg over one year (13).

The studies included in the meta-analyses varied substantially with respect to study design, exposure assessment, adjustment for covariates, and specific outcomes evaluated and this relatively high degree of unexplained heterogeneity observed in the analyses might limit the validity of the summary estimates (13). However, all of the cohort studies included in the meta-analysis were adjusted for potential confounding by various diet and lifestyle factors, and for most, a positive association was still observed, suggesting an independent effect of sugar-sweetened beverage consumption. Furthermore, risk of bias assessment suggested that most cohort studies were of good quality and the majority of trials had a low or unclear risk of bias for the variables that were evaluated. In contrast to previous meta-analyses, Malik et al. conducted separate analyses for prospective cohort studies and trials, qualitatively reviewed studies that were not included in their analyses, and separately evaluated prospective cohort studies that used a change versus change analysis (that is, studies which correlated a specified serving size of sugar-sweetened beverages to a quantified change in body weight) (13). Notably, while overweight and obesity are growing problems in low- and middle-income countries, no studies conducted in adults were identified in these settings.

Conclusion

The systematic review and meta-analysis by Malik et al. (13) and the majority of earlier studies support the view that decreasing sugar-sweetened beverage consumption will reduce the prevalence of obesity and obesity-related diseases (17). If this is so, then public health measures addressing sugar-sweetened beverage consumption should be put in place as soon as possible, especially in low- and middle-income countries where the rates of obesity, overweight and diet-related noncommunicable diseases are rapidly increasing and placing additional demands on already over-burdened health systems. The WHO Global action plan on the prevention and control of noncommunicable diseases 2013–2020 (18) urges countries to reduce modifiable risk factors for noncommunicable diseases, including unhealthy diets, and underlying social determinants through creation of health-promoting environments. In addition to practical knowledge being acquired on various nutrition interventions targeting diet-related noncommunicable diseases, national experience with well-designed taxes on unhealthy food and beverages is growing (19). Many national societies and organizations have called for reductions in consumption of sugar-sweetened beverages to help prevent obesity and improve overall health. The results of the meta-analysis by Malik et al. offer additional support for these recommendations by providing a strong evidence-base for ramping up measures to reduce the intake of sugar-sweetened beverages as part of a larger effort to address the growing epidemic of overweight and obesity.

References

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16. Pan A, Malik VS, Hao T, Willett WC, Mozaffarian D, Hu FB. Changes in water and beverage intake and long-term weight changes: results from three prospective cohort studies. Int J Obes (Lond). 2013; 37(10):1378-85.

17. Hu FB. Resolved: there is sufficient scientific evidence that decreasing sugar-sweetened beverage consumption will reduce the prevalence of obesity and obesity-related diseases. Obesity Reviews. 2013; 14(8):606-619.

18. WHO. Global action plan for the prevention and control of noncommunicable diseases. 2013-2020. Geneva: World Health Organization; 2013. (http://apps.who.int/iris/bitstream/10665/94384/1/9789241506236_eng.pdf?ua=1, accessed 12 April 2014)

19. OECD. Obesity update 2012. OECD; 2012. (www.oecd.org/health/49716427.pdf, accessed 12 April 2014)

Disclaimer

The named authors alone are responsible for the views expressed in this document.

Declarations of interests

Conflict of interest statements were collected from all named authors and no conflicts were identified.