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LETTER TO THE EDITOR |
Department of Preventive Medicine and Public Health
Medical School–Clinica Universitaria
c/Irunlarrea
1 Ed Investigación
31008 Pamplona
University of Navarra
Spain
E-mail: mamartinez{at}unav.es
Dear Sir:
We read with great interest the meta-analysis by Forshee et al (1) in the June 2008 issue of the Journal. It is at least curious that 2 other studies on the same topic were simultaneously published in other journals (2, 3). Both of these studies suggest at least a partial role of sugar-sweetened beverages (SSBs) on weight gain among children and adolescents. Another study published in 2007 that was not included in the meta-analysis also suggested a detrimental effect of SSBs (4). In addition, some methodologic issues are worthy of consideration.
Although not statistically significant, most of the point estimates in the meta-analysis showed a positive association, albeit of low magnitude. Alternative explanations to a low-magnitude effect are compatible with these results, and the true effect might be of greater magnitude. Children and adolescents, and their parents as well, might be prone to underreporting consumption of these types of beverages, because of a well-known social desirability bias. This would be translated into a nondifferential misclassification that very likely leads the estimates of effect toward the null value. This nondifferential misclassification bias, in addition to the unavoidable measurement error of nutritional epidemiologic studies, may be an alternative explanation of the almost null findings. Of greater concern, and at the same time also possible, is the likelihood that obese subjects may systematically underreport consumption of SSBs more than do their nonobese counterparts. There is empirical evidence supporting this hypothesis (5). This would lead to a differential misclassification that would also mask or attenuate any important result.
We should not forget that this meta-analysis was based only on children and adolescent populations. Thus, as the authors indicated in the discussion section, its conclusions cannot be generalized to the adult population. Therefore, this meta-analysis is not directly comparable with the previous systematic review by Malik et al (6), for which some of the studies were conducted in adults. Specifically, >70% of the total participants in the 10 longitudinal studies reviewed by Malik et al were adults. It seems unfair to include a quote (6; page 274) from this previous systematic review in the discussion of the Forshee meta-analysis (1; page 1670) without any clarification that the study populations of both systematic reviews were different.
Although the overall results were not entirely consistent, and the effect on body weight was nonremarkable at first look, it was substantial for a single food group, especially if it accumulates in the long term. As the authors quoted in the discussion, SSBs are a source of energy. However, this statement is incomplete because SSBs not only contribute to excess energy intakes, but they provide no nutritional benefit. Even though the overall effect on weight gain might appear relatively small, there is no doubt that the alternative of replacing SSBs with water (no calories) does help to reduce total energy intake. This will translate to large long-term benefits because the cumulative effects of small increases in daily energy intakes lead to weight gain and obesity (7). Avoidance of these cumulative effects contributes to the prevention of diabetes and cardiovascular disease.
The advice by Forshee et al to consume SSBs in moderation is mainly of interest for food marketing purposes (8); however, from a public health perspective, it may be naive and potentially harmful. The relative intellectual and psychological immaturity of the young and the complexity of growth and development of adolescents speak against sending them this ambiguous message of consuming SSBs in moderation (9).
We agree that more research is needed to achieve well-established evidence in this field. However, in the meantime, because doubt exists, less harmful advice to the entire population would be to replace the consumption of SSBs with water to comply with the need for good hydration.
ACKNOWLEDGMENTS
The authors had no conflicts of interest.
REFERENCES
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