Do high vs. low purchasers respond differently to a nonessential energy-dense food tax? Two-year evaluation of Mexico's 8% nonessential food tax.

It is unclear whether response to a nonessential food tax varies across time or for high vs. low-consuming households. The objective is to examine whether the effect of Mexico's 2014 8% nonessential energy-dense foods tax increased in the second year post-implementation and whether it differentially affected households by pre-tax purchasing pattern. We used longitudinal data on Mexican household food purchases (n=6089 households) from 2012 to 2015. Households were classified based on median pre-tax purchases: low untaxed/low taxed ("low"), low untaxed/high taxed ("unhealthy"), high untaxed/low taxed ("healthy"), and high untaxed/high taxed ("high") purchasers. Fixed effects models tested whether observed post-tax purchases differed from the counterfactual, or what would have been expected based on pre-tax trends. Post-tax declines in the % taxed food purchases increased from -4.8% in year one to -7.4% in year two, yielding a 2-year mean decline of 6.0% beyond the counterfactual (p<0.01). Post-tax change in % taxed food purchases varied by pre-tax purchasing level. Healthy purchasers showed no post-tax change in % taxed food purchases beyond the counterfactual, while unhealthy, low and high purchasers decreased (-12.3%, -5.3% and -4.4%, respectively) (p<0.01). The positive effect of Mexico's junk food tax continued in the second year, and households with greater preferences for taxed foods showed a larger decline in taxed food purchases.