To examine changes in sales of highly processed foods, including infant formulas, in countries joining free trade agreements (FTAs) with the US.

Annual country-level data for food and beverage sales come from Euromonitor International. Analyses are conducted in a comparative interrupted time-series (CITS) framework using multivariate random-effects linear models, adjusted for key confounders: gross domestic product (GDP) per capita, percent of the population living in urban areas and female labor force participation rate. Memberships in other FTAs and investment treaties are also explored as possible confounders.

Changes are assessed between 2002 and 2016.

Ten countries joining US FTAs are compared with eleven countries without US FTAs in force; countries are matched on national income level, world region and World Trade Organization membership.

After countries join a US FTA, sales are estimated to increase by: 0·89 (95 % CI 0·16, 1·6; P = 0·016) kg per capita per annum for ultra-processed products, 0·81 (95 % CI 0·47, 1·1; P < 0·001) kg per capita per annum for processed culinary ingredients and 0·17 (95 % CI 0·052, 0·29; P = 0·005) kg per capita under age 5 per annum for baby food. No significant change is estimated for minimally processed foods. In statistical models, large unexplained variations in country-specific trends suggest additional unmeasured country-level factors also impact sales trends following entry into US FTAs.

These findings strongly support the conclusion that joining US FTAs can contribute to detrimental changes in national dietary consumption that increase population risk of non-communicable diseases.