Will a tax on soda reduce consumption and lead to a reduction in weight and obesity?
Despite the “disappointing” quality of the evidence linking soda to weight gain, proponents of soda taxes tend towards selectively citing studies which offer the strongest support for their conclusions when arguing for implementation.
In “Ounces of Prevention – The Public Policy Case for Taxes on Sugared Beverages,” which was published in the New England Journal of Medicine, Kelly Brownell, a psychologist who directs the Rudd Center for Nutrition and Obesity at Yale University, and Thomas Frieden, now Director of the Centers for Disease Control, cite only the Vartanian et al. systematic review in support of the link between SSBs and weight gain, ignoring all the others. As Brownell is a co-author of this paper, he is, in effect, citing himself; and he does so to claim that“Sugar sweetened beverages… may be the single largest driver of the obesity epidemic” [emphasis added to denote speculation].
Vartanian is again cited by Brownell et al. in “The Public Health and Economic Benefits of Taxing Sugar-Sweetened Beverages,” which was also published in the New England Journal of Medicine. Malick is also referenced, while Forshee et al. was dismissed as erroneous and funded by the beverage industry.
And a third, recently published paper with Brownell as a co-author, “Estimating the potential of taxes on sugar-sweetened beverages to reduce consumption and generate revenue,” (Preventative Medicine, in publication) cites Vartanian and Malik for an association between soda and obesity.
Another paper put out by the US Department of Agriculture, “Taxing Caloric Sweetened Beverages: Potential Effects on Beverage Consumption, Calorie Intake and Obesity,” (Travis et al.) cites the Vartanian and Malick reviews, which both assert a “strong” association between SSBs and weight gain, while ignoring reviews such as Bachman et al. and Pereira et al. that don’t. Remarkably, Travis et al. seem unaware of the conclusions of their department’s own advisory committee on nutrition.
Similarly, the paper “Can Soft Drink Taxes Reduce Population Weight” (Fletcher et al.) cites Vartanian and Malik for the link.
A soda tax, of course, is meaningless if there isn’t a strong link between consumption and weight gain, so it’s understandable that advocacy papers or economic models should cleave to the strongest evidence for such a link. However, given the problems associated with these systematic reviews, selective citation admits the possibility that these tax proposals may be nothing more than intellectual exercises in wishful thinking. Interestingly, the proliferation of soda tax proposals based on the assumption that there is strong evidence for a link with obesity itself becomes a justification for further soda tax proposals, such as Finkelstein et al.’s “Impact of Targeted Beverage Taxes on Higher- and Lower-Income Households.”
The best place to start in looking at the economic evidence for soda taxation is at the soda taxes currently in place.
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