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, leading to the development of behavioral disorders including depressive behavior and cognitive alterations. These behavioral alterations cease along with the synthesis of brain cytokines. When the level of expression of these cytokines remains high, they become toxic to neurons and can lead to their death, as in the case of neurodegenerative disorders like Alzheimer’s disease. Omega3 (ω3) type polyunsaturated fatty acids (PUFAs) are essential nutrients and essential components of neuronal and glial cell membranes. Additionally, they have powerful immunomodulatory properties and regulate the cytokines and their signaling pathways. They accumulate in the brain during the perinatal period in a dietary supply-dependant fashion. Their brain levels diminish with age, but can be corrected by a diet enriched in ω3 PUFAs. The increasing exposure of the population to “fast-food” type diets, extremely unbalanced in ω3 PUFAs, could contribute to the fragilization of the brain with respect to cytokines.