Global Objective The global objective of this population-based randomized controlled trial is to investigate whether the intake of 30 g of walnut kernels (or ~1.5g of n-3 PUFA) per day is beneficial for brain development among teenagers. The combination of sophisticated tools for assessing brain functions, such as computerized neuropsychological tests, will provide the precise data required to detect even subtle changes in brain development resulting from the effects of the nutritional intervention. Further assessments using behavioural rating scales will give us a wider look of the potential effects of the intervention.