Long-chain polyunsaturated fatty acids, walnuts and brain development Nutrition during pregnancy, lactation, childhood and adolescence has a fundamental influence on overall development. Essential fatty acids are long chain polyunsaturated acids (LCPUFAs) that the body cannot synthesize by itself, and must be obtained through the diet (mainly from oily fish, seeds and nuts). Three of these fatty acids play an essential role in brain development: omega-3 (docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids) and omega-6 (arachidonic acid (AA)) (McCann, 2005). LCPUFAs comprise approximately 15 to 30% of the brain's dry weight (Hallahan, 2005), and are involved in the function and architecture of the central nervous system throughout various stages of life. Studies show that DHA regulates neurotransmission systems such as serotonergic, dopaminergic, norepinephrinergic, and acetylcholinergic systems (Fontani, 2005). Of all edible plants, walnuts have the highest level of the omega-3 fatty acid, alpha-linolenic acid (ALA). ALA is the precursor for DHA and EPA, the two most essential fatty acids for the brain (Carey, 2013). Walnuts are also rich in fiber, vitamins, minerals, and other bioactive substances, such as phenolic antioxidants and phytosterols (Bao, 2013). Several studies have confirmed an increment in blood n-3 PUFA levels and improvements in lipid profile after a short-term intervention of a few walnuts per day (Marangoni, 2007; Maranhao, 2011). While most human studies have shown the cardiovascular benefits of walnut intake (Poulose, 2014), there is a need to investigate the potential beneficial effects on brain development, some incipient research on adults show positive results in cognition, these results are further described in Background section (Pribis, 2012; Sánchez-Villegas, 2011). These findings in adults provide a proof of concept for the potential brain development benefits of walnuts, which never has been studied among young teenagers.