AbstractBackground: Adolescence is a critical period for brain development, coinciding with increased dietary autonomy and exposure toultra-processed foods. Poor diet quality is associated with cognitive impairment and mental health disorders, yet integrated evidence linking these outcomes remains sparse. Objective: To synthesize evidence from biological mechanisms, observational studies, longitudinal cohorts, and randomized controlled trials (RCTs) examining the relationship between diet quality and cognitive performance, academic achievement, and mental health in children and adolescents.Methods: Comprehensive narrative review integrating 41 peer-reviewed studies (2009-2025), including 8 systematic reviews/metaanalyses, 8 RCTs and longitudinal cohorts, and 13 cross-sectional observational studies from multiple countries (Brazil, Spain, Canada, Australia, Chile, Iran, China, South Korea, Sweden, Portugal).Results: Converging evidence demonstrates that poor diet quality (characterized by high consumption of ultra-processed foods and sugar-sweetened beverages, and low consumption of fruits, vegetables, and whole grains) is associated with: 1 impaired cognitive domains (memory, executive function, processing speed); 2 lower academic performance (GPA and standardized test scores); and 3 increased depressive and anxiety symptoms. Three mechanistic pathways emerge: nutrient deficiency impairing structural brain development; ultra-processed foods promoting neuroinflammation, gut dysbiosis, and blood-brain barrier dysfunction; and mental health mediation, whereby depression and anxiety directly impair cognitive capacity. Brief dietary interventions (3-8 weeks) in young adults and adolescents reduce depressive symptoms by moderate-to-large effect sizes (d = 0.36-0.75), sustained at follow-up.Conclusion: Integrated evidence supports improving diet quality during childhood and adolescence as a scalable strategy to protect cognitive development and reduce mental health burden, with mechanisms operating through nutrient adequacy, reduction of neuroinflammation, and mental health protection.
Thaís Cachuté Paradella (Fri,) studied this question.