Changes in sugar-sweetened beverages and non-essential energy-dense food purchases overall and by type before and after the implementation of taxes in Mexico: repeated cross-sectional national surveys (2008-2018).

Background: In January 2014, the Mexican federal government implemented a tax to sugar-sweetened beverages of 1 peso per litre and an 8% tax to non-essential energy-dense foods. Prior studies have evaluated the association of these taxes on household purchases, but none considered the potential heterogeneity of purchases by type of store. We aimed to estimate the impact of the taxes on food and beverage purchases in Mexican households overall and by type of store. Methods: We estimated changes in the quantity purchasesd of taxed and untaxed food and beverages using six rounds of the Mexican National Household Income and Expenditures Survey, which are repeated cross-sectional surveys. To estimate changes in purchases, we used a two-part model, testing for interactions by type of store to assess effect modifications. Results: During the 4 years after the implementation of the taxes, purchases of non-essential energy-dense foods and sugar-sweetened beverages decreased on average by -7.0% and -4.4%, respectively. There was also a slight decrease in purchases of untaxed foods (-1.7%), while untaxed beverages increased by 10.9%. The largest reductions for taxed foods were found in small neighbourhood stores (-19.0%). We did not observe significant heterogeneity in the remaining types of stores. For SSBs, public markets showed the largest decrease (-22.7%) followed by small neighbourhood stores (-11.4%), while increases were observed in convenience stores (44.8%) and other stores (22.2%). The high increases in convenience and other stores suggest that taxes may not be fully passed on to prices, that promotional pricing was used to offset the tax or that these increases reflect secular trends. Conclusion: Despite the modest amounts of taxes in Mexico, reductions in purchases were documented 4 years after implementation, emphasising the potential benefits of increasing the taxes. Heterogeneity in purchases by store types suggests the need to analyse differences in the tax pass-through and its mechanisms at the store level.