BACKGROUND: Understanding the role of maternal diet in early brain development is critical, as pregnancy represents a period of significant vulnerability and growth for the developing brain. OBJECTIVES: This study aims to assess the association between maternal nuts, total seafood, and large fatty fish consumption during pregnancy and offspring neuropsychological function ≤15 y, considering the potential mediation of omega-3 fatty acids. METHODS: This study was part of The Spanish Childhood and Environment birth cohort, following 1737 mother-child pairs from pregnancy to age 15. Maternal diet was evaluated using a semiquantitative food frequency questionnaire, whereas children's neuropsychological function was measured through standardized computer-based tests. Attention (hit reaction time and its variability, HRT and HRT-SE) was measured with the Conners' Kiddie Continuous Performance Test and the Attention Network Test. Working memory (detectability in 2-back, d2', and 3-back tasks, d3') was evaluated using the N-back task. Fluid intelligence was assessed with Raven's Progressive Matrices and the Test of Primary Mental Abilities. Linear mixed-effects regression models assessed the association of nuts, seafood and large fatty fish with neuropsychological outcomes, whereas generalized structural equation modeling was used for mediation analyses. RESULTS: Higher maternal nut consumption was significantly linked to improved attention [HRT-SE β = -0.05, 95% confidence interval (CI): -0.09, -0.00] and working memory (d2' β = 0.05, 95% CI: 0.00, 0.09, and d3' β = 0.06, 95% CI: 0.02, 0.11) in offspring. Greater consumption of large fatty fish was associated with better attention (HRT-SE β = -0.06, 95% CI: -0.10, -0.02
and HRT β = -0.04, 95% CI: -0.08, -0.00), and fluid intelligence (β = 0.08, 95% CI: 0.02, 0.13). Omega-3 fatty acids mediated 8%-14% of these effects on attention. CONCLUSIONS: Maternal diet at pregnancy and omega-3 intake may support long-term cognitive development in children and adolescents.