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Am J Clin Nutr 89: 438-439, 2009. First published December 3, 2008; doi:10.3945/ajcn.2008.26980
 American Journal of Clinical Nutrition, doi:10.3945/ajcn.2008.26980
Vol. 89, No. 1, 438-439, January 2009
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© 2009 American Society for Clinical Nutrition

Sugar-sweetened beverages and BMI in children and adolescents: reanalyses of a meta-analysis

Vasanti S Malik, Walter C Willett and Frank B Hu

Departments of Nutrition and Epidemiology, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, E-mail: vmalik{at}hsph.harvard.edu

Dear Sir:

In a recent issue of the Journal, Forshee et al (1) reexamined current epidemiologic and clinical trial evidence on the relation between sugar-sweetened beverages (SSBs) and body mass index (BMI; kg/m2) in children and adolescents. The conclusion of their meta-analysis, which was supported by the beverage industry, contradicts those drawn from several other reviews (2–4). A previous systematic review and meta-analysis on the same topic reported "clear associations of soft drink intake with increased caloric intake and body weight" (4). We believe that the reasons for the discrepant results between Forshee et al and others stem from analytic errors in their meta-analysis.

We were alerted to a potential problem because the percentage weights for several studies in the Forshee analysis, as shown in their forest plot, appeared to be incorrect. For example, the weights for studies by Blum et al (5) and Newby et al (6) were suspiciously high compared with other much larger studies, such as those by Ludwig et al (7) and Berkey et al (8). Because study weights are related to the inverse of the variance of the coefficients, larger studies generally have smaller variances and are thus expected to have larger weights. Because Forshee et al expressed their results as the change in BMI units per 12-oz serving of change of SSB, scaling factors were applied to estimates from some studies to obtain unit consistency. However, estimates from Blum and Newby, both of which are expressed as change per 1-oz serving of SSB in their original publications, were not scaled. We conducted a meta-analysis on the same data using scaled coefficients and SEs and found greatly reduced study weights, larger estimates, and wider CIs for these studies compared with analyses by Forshee et al (Figure 1A). Because the methods used to transform the estimates by Phillips to the required units for the meta-analysis were unclear, we used those reported by Forshee et al. In addition, our weights are summarized using random-effects analysis, which is the preferred method compared with the fixed-effects analysis in the presence of study heterogeneity. Forshee et al reported study weights from the inverse variance fixed-effects analysis, despite having a high degree of heterogeneity between studies (I2 = 73.9%). In our analysis, where available, we also used coefficients that were not adjusted for total energy intake. Because the association between SSB consumption and BMI is mediated in part by overall energy intake, adjusting for energy will tend to underestimate the effect of these beverages on body weight. Forshee et al used results in their analysis that were adjusted for energy and mention that the impact of using unadjusted values on their overall effect estimate was minimal. However, if analyzed separately and weighted properly, studies with energy-adjusted estimates (5, 6, 9, 10) show a nonsignificant inverse trend (–0.03; 95% CI: –0.11, 0.04), whereas those with unadjusted estimates (7, 8, 11–13) show a positive association (0.08; 95% CI: 0.03, 0.13), suggesting the presence of bias in Forshee et al's analysis. Results from a meta-regression that used adjustment for energy as a predictor of effect confirm these findings (P = 0.048) and provide statistical rationale for using unadjusted estimates in the analysis.


Figure 1
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  		FIGURE 1. A: Forest plot of studies of sugar-sweetened beverage consumption and BMI (kg/m2) in children and adolescents. Random-effects estimate (DerSimonian and Laird method). B: Forest plot of studies of sugar-sweetened beverage consumption and BMI in children and adolescents with estimates that are not adjusted for total energy intake. ES, reported estimate for the predicted change in BMI per change in 12-oz serving of sugar-sweetened beverage.

 
Overall, our findings, in contrast to those by Forshee et al, clearly suggest a positive association between SSB intake and BMI among children. The analyses without adjustment for total energy as shown in Figure 1B are more likely to reflect the true association, although this will still be underestimated because of measurement error in dietary assessment. However, the studies in this literature are heterogeneous by nature, with varying lengths of duration, age of participants, methods of exposure and outcome assessment, design (intervention compared with observational), and units of expression. For these reasons, to fully understand the relation between SSB intake and BMI, particularly among children and adolescents who are still growing, studies need to be examined individually with greater emphasis placed on higher quality studies that are adequately powered, with appropriately long periods of follow-up, and use of robust assessment methods (eg, a single 24-h recall provides a poor assessment of an individual's diet). As discussed in previous systematic reviews (3, 4), discouraging consumption of sugary beverages is an important way to achieve and maintain a healthy body weight in children and adults.

ACKNOWLEDGMENTS

No conflicts of interest were declared.

REFERENCES

  1. Forshee, RA, Anderson, PA & Storey, ML. Sugar-sweetened beverages and body mass index in children and adolescents: a meta-analysis. Am J Clin Nutr 2008;87:1662–71..[Medline]
  2. Bray, GA, Nielsen, SJ & Popkin, BM. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr 2004;79:537–43..[Abstract/Free Full Text]
  3. Malik, VS, Schulze, MB & Hu, FB. Intake of sugar-sweetened beverages and weight gain: a systematic review. Am J Clin Nutr 2006;84:274–88..[Abstract/Free Full Text]
  4. Vartanian, LR, Schwartz, MB & Brownell, KD. Effects of soft drink consumption on nutrition and health: a systematic review and meta-analysis. Am J Public Health 2007;97:667–75..[Abstract/Free Full Text]
  5. Blum, JW, Jacobsen, DJ & Donnelly, JE. Beverage consumption patterns in elementary school aged children across a two-year period. J Am Coll Nutr 2005;24:93–8..[Abstract/Free Full Text]
  6. Newby, PK, Peterson, KE, Berkey, CS, Leppert, J, Willett, WC & Colditz, GA. Beverage consumption is not associated with changes in weight and body mass index among low-income preschool children in North Dakota. J Am Diet Assoc 2004;104:1086–94..[Medline]
  7. Ludwig, DS, Peterson, KE & Gortmaker, SL. Relation between consumption of sugar-sweetened drinks and childhood obesity: a prospective, observational analysis. Lancet 2001;357:505–8..[Medline]
  8. Berkey, CS, Rockett, HR, Field, AE, Gillman, MW & Colditz, GA. Sugar-added beverages and adolescent weight change. Obes Res 2004;12:778–88..[Medline]
  9. Striegel-Moore, RH, Thompson, D, Affenito, SG, et al.. Correlates of beverage intake in adolescent girls: the National Heart, Lung, and Blood Institute Growth and Health Study. J Pediatr 2006;148:183–7..[Medline]
  10. Mundt, CA, Baxter-Jones, AD, Whiting, SJ, Bailey, DA, Faulkner, RA & Mirwald, RL. Relationships of activity and sugar drink intake on fat mass development in youths. Med Sci Sports Exerc 2006;38:1245–54..[Medline]
  11. James, J, Thomas, P, Cavan, D & Kerr, D. Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial. BMJ 2004;328:1237..[Abstract/Free Full Text]
  12. Phillips, SM, Bandini, LG, Naumova, EN, et al.. Energy-dense snack food intake in adolescence: longitudinal relationship to weight and fatness. Obes Res 2004;12:461–72..[Medline]
  13. Ebbeling, CB, Feldman, HA, Osganian, SK, Chomitz, VR, Ellenbogen, SJ & Ludwig, DS. Effects of decreasing sugar-sweetened beverage consumption on body weight in adolescents: a randomized, controlled pilot study. Pediatrics 2006;117:673–80..[Abstract/Free Full Text]



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