Measuring weight outcomes for obesity intervention strategies: the case of a sugar-sweetened beverage tax.

Taxing unhealthy foods has been proposed as a means to improve diet and health by reducing calorie intake and raising funds to combat obesity, particularly sugar-sweetened beverages (SSBs). A growing number of studies have examined the effects of such food taxes, but few have estimated the weight-loss effects. Typically, a static model of 3500 calories for one pound of body weight is used, and the main objective of the study is to demonstrate its bias. To accomplish the objective, we estimate income-segmented beverage demand systems to examine the potential effects of a SSB tax. Elasticity estimates and a hypothetical 20 percent effective tax rate (or about 0.5 cent per ounce) are applied to beverage intake data from a nationally representative survey, and we find an average daily reduction of 34-47 calories among adults and 40-51 calories among children. The tax-induced energy reductions are translated into weight loss using both static and dynamic calorie-to-weight models. Results demonstrate that the static model significantly overestimates the weight loss from reduced energy intake by 63 percent in year one, 346 percent in year five, and 764 percent in year 10, which leads to unrealistic expectations for obesity intervention strategies. The tax is estimated to generate $5.8 billion a year in revenue and is found to be regressive, although it represents about 1 percent of household food and beverage spending.