The innate immune system of the brain is principally composed of microglial cells and astrocytes, which, once activated, protect neurons against insults (infectious agents, lesions, etc.). Activated glial cells produce inflammatory cytokines that act specifically through receptors expressed by the brain. The functional consequences of brain cytokine action (also called neuroinflammation) are alterations in cognition, mood and behaviour, a hallmark of altered well-being. In addition, proinflammatory cytokines play a key role in depression and neurodegenerative diseases linked to aging. Polyunsaturated fatty acids (PUFA) are essential nutrients and essential components of neuronal and glial cell membranes. PUFA from the diet regulate both prostaglandin and proinflammatory cytokine production. n-3 fatty acids are anti-inflammatory while n-6 fatty acids are precursors of prostaglandins. Inappropriate amounts of dietary n-6 and n-3 fatty acids could lead to neuroinflammation because of their abundance in the brain and reduced well-being. Depending on which PUFA are present in the diet, neuroinflammation will, therefore, be kept at a minimum or exacerbated. This could explain the protective role of n-3 fatty acids in neurodegenerative diseases linked to aging.