Rising food prices and widening nutrition gaps in Mexico: The cost of nutrient-dense and ultra-processed foods before, during, and after COVID-19.

The COVID-19 pandemic disrupted global food systems, contributing to rising food prices and altering the affordability of healthy diets. This study examined the relationship between nutrient density of foods, food prices and inflation in Mexico before, during, and after the pandemic. Foods from the ENSANUT dietary survey were assigned to 4 categories using the NOVA classification system and were linked to nutrient composition data and national food price series from 2012 to 2025. The Nutrient Rich Food Index (NRF9.3) was a measure of nutrient density. Affordability was defined as nutrient density relative to price per 100 kcal. Trends in prices and inflation were analyzed using a panel data model with food-level fixed effects. Minimally processed foods had substantially higher nutrient density (NRF9.3: 202.2) than processed (15.7) and ultra-processed foods (UPFs; 5.4), but were also markedly more expensive per 100 kcal. Across the study period, higher nutrient density was consistently associated with higher prices per calorie. During the pandemic, inflation for minimally processed foods increased by 1.64 percentage points (p.p.; p = 0.064) relative to pre-pandemic levels, and by 6.04 p.p. in the post-pandemic period (p < 0.001). Processed foods and culinary ingredients experienced additional inflation of 1.99 p.p. and 1.21 p.p., respectively, during the pandemic, while no significant differences across processing categories were observed post-pandemic. Following the onset of the pandemic, food prices increased across all processing categories. Because minimally processed foods had higher baseline prices, similar inflation rates translated into a widening affordability gap between more and less nutritious foods. These findings suggest that foods aligned with dietary recommendations became relatively less affordable during a period of economic disruption, potentially incentivizing substitution toward lower-cost, energy-dense UPFs. Policies that improve the affordability and price stability of nutrient-dense foods may be critical to support healthy diets under conditions of economic volatility.