Abstract
IMPORTANCE: Ultraprocessed foods (UPF) contribute to nearly half of energy intake among preschool-aged children in Canada, yet their impact on behavioral and emotional functioning remains underexplored. OBJECTIVE: To examine the associations between UPF intake at age 3 years and behavioral outcomes at age 5 years. DESIGN, SETTING, AND PARTICIPANTS: This cohort study included children with dietary and behavioral data from September 2011 to April 2018 in the CHILD Cohort Study, a prospective Canadian pregnancy cohort. Data analysis was done between February to July 2025. EXPOSURE: UPF intake at age 3 years was assessed by a 112-item food frequency questionnaire and categorized using the NOVA system. MAIN OUTCOMES AND MEASURES: Behavior was measured using the validated Child Behavior Checklist (CBCL; range 0-100; higher scores indicating more adverse symptoms). UPF intake measured as a continuous percentage of energy was examined using multivariable-adjusted linear regression models accounting for maternal diet, birth factors, infant feeding, and sociodemographic and early-childhood characteristics. A multivariable-adjusted substitution model estimated the association of statistically replacing 10% energy from UPF with minimally processed foods (MPF) among all children. RESULTS: Among 2077 participants, 1092 (52.6%) were male; 1376 children (66.2%) were White, 480 children (23.1%) were multiracial, and 221 children (10.7%) were identified as another ethnic group. At age 3 years, UPF contributed a mean (SD) of 45.5% (11.6%) of total energy intake. At age 5 years, the mean (SD) CBCL scores were 44.6 (9.1) for internalizing, 39.6 (9.4) for externalizing, and 41.2 (9.0) for total behavior. Each 10% increase in energy from UPF was associated with higher CBCL internalizing (β = 0.81 [95% CI, 0.43 to 1.19]), externalizing (β = 0.47 [95% CI, 0.08 to 0.87]), and total (β = 0.64 [95% CI, 0.27 to 1.01]) scores. Substitution of 10% energy from UPF with MPF was associated with lower internalizing (β = -0.91 [95% CI, -1.33 to -0.49]), externalizing (β = -0.49 [95% CI, -0.93 to -0.06]), and total (β = -0.70 [95% CI, -1.12 to -0.29]) scores. CONCLUSIONS AND RELEVANCE: In this cohort study of preschoolers in Canada, higher UPF intake was associated with adverse behavioral and emotional symptoms by age 5 years. These findings suggest that replacing UPF with MPF during the preschool years may support healthier behavioral development, with potential benefits for long-term mental health. These findings also support ongoing policy actions that promote MPF and underscore the need for early-life dietary interventions.