Giammattei et al1 found that both diet and sugar-sweetened soft drinks were positively associated with obesity and concluded that "it is not the calories in drinks per se that are responsible for this association." We are surprised by this assertion, in view of the methodological limitations of their study. The design was cross-sectional in nature, and very few relevant covariates were examined in statistical models. Therefore, the potential for confounding and reverse causality must be carefully weighed. As the authors acknowledge, obese children are probably more likely to drink diet soda, a fact that might explain entirely the observed association. We conducted a prospective observational study of soft drinks and obesity during 2 academic years and sought to control for multiple demographic, dietary, and behavioral confounders (including whether the child was exercising to lose weight).2 We found that sugar-sweetened drinks were positively associated, while diet drinks were negatively associated with the odds ratio of obesity. Two intervention studies found that energy intake and/or body weight increased among subjects given sugar-sweetened drinks but decreased among subjects given diet drinks.3,4 Moreover, a meta-analysis of studies conducted during a 25-year period demonstrated that humans compensate poorly for calories consumed in liquid form.5 We agree with the authors that more research is needed into the effects of beverages on body weight, but must disagree with their contention that the calories in these beverages do not matter.
Ludwig DS, Ebbeling CB, Peterson KE, Gortmaker SL. Hard Facts About Soft Drinks. Arch Pediatr Adolesc Med. 2004;158(3):290. doi:10.1001/archpedi.158.3.290-a