Changes in taxed food and beverages purchases by type of store and changes in weight trends in Mexican preschoolers after the implementation of taxes in Mexico / Claudia Gabriela García Chavez

Tesis (Doctorado en Ciencias en Nutrición Poblacional) - Escuela de Salud Pública de México. INSP, 2023

ABSTRACT
Introduction: In January 2014, the Mexican government implemented a tax on
sugar-sweetened beverages (SSB) of one peso per liter and an 8% tax on
nonessential energy-dense foods (NEDF) as a package of key strategies to improve
population´s diet. Prior studies have evaluated the association of these taxes on
household purchases or in health outcomes (i.e., body mass index, or body weight)
with microsimulations studies among the Mexican population; however, none have
considered the potential heterogeneity of purchases by type of store with national
survey data and, the potential impact on weight gain among preschool children using
longitudinal data from administrative records.
Aims: To examine the association of the taxes on food and beverage purchases in
Mexican households by type of store (street market, supermarket, small
neighborhood stores, convenience store, specialty stores, and others). This overall
aim was divided into two specific aims: 1) To estimate the impact of the taxes on
food and beverage purchases in Mexican households by type of store (street market,
supermarket, small neighborhood stores, convenience store, specialty stores, and
others); and 2) To estimate the change in body weight in Mexican preschoolers from
daycare centers of the Mexican Institute of Social Security (IMSS, Spanish
acronym).
Methods: For the first aim, we analyzed six rounds of the Mexican National
Household Income and Expenditure Survey (ENIGH, for his acronym in Spanish)
from 2008 to 2018, household information on food and beverage purchases before
and after the implementation of the tax were included. To estimate changes in
purchases overall and by store type, we used a two-part model to assess the
probability of purchase and the amount purchased among purchasers. We stratified
the models by type of store to assess the potential effect modification of the tax on
purchases. For the second aim, We analyzed administrative data containing
anthropometric measures of 39,402 preschool children who attended public daycare
centers in Mexico from 2013 to 2014. Regression models for panel data using fixed
effects were performed to estimate changes in body weight by comparing the pre-
(Jul-Dec 2013) and post-tax (Jan-Jun 2014) trends, adjusted by length/height and
age. A sensitivity analysis was performed on 39,206 children of the same age by
considering a pre-tax period between Jul-Dec 2012 (2012 trend) and Jan-Jun 2013
(2013 trend) as a falsification test. In both scenarios, we stratified the analysis by
sex, baseline age, nutritional status, and geographic region.
Results: For the first aim, we found that after the implementation of the taxes,
purchases of NEDF and SSB decreased by 6% and 4.8%, respectively. There were
no changes in purchases of untaxed foods while untaxed beverages rose by 10.8%.
The largest reductions for taxed foods were found in “small neighborhood stores” (-
19.1%; -9.4 g/capita/week) and “supermarkets” (-10.3%; -3.9 g/capita/week) .
Similarly, for SSB “small neighborhood stores” showed the largest decrease -12.4%,
-104.8ml/capita/week) followed by “supermarkets” (-12.2%, -13.7ml/capita/week).
For the second aim, we observed an association between the taxes on NEDF and
SSB and the change in weight in Mexican preschoolers. There was a slightly higher
significant reduction in body weight after the implementation of the tax among
overweight children (-0.421 kg/month), and, in the regionally stratified analysis, we
found that the changes were driven by higher significant decreases in weight in the
post-policy period among children who lived in Mexico City and the Center-North
region of the country (-0.082 and -0.107 kg/month, respectively). However, the
findings are similar to those reported in the falsification test.
Conclusion
In Mexico, taxes on NEDF and SSB have been documented to have an effect on the
reduction of purchases of these unhealthy products, however, more research is
needed to better understand the potential effect on health outcomes by reducing
weight and thus impact on the prevalence of overweight, obesity, and related NCDs.
This work adds evidence to the body of literature that supports the positive public
health-related effects of such taxes.