The present mismatch between what our brain needs, and the modern diet neglects our marine heritage. Last century, the priority in nutrition and food production was to achieve a high protein diet and somatic growth and function. The dietary content of omega-3 (N-3) required by the brain was neglected although evidence for the essentiality of certain fatty acids was published in 1929 and specifically re-affirmed for omega 3 in the brain in the 1970s.

Cognitive decline with age and neurodegenerative disorder with dementia are now rising. This review describes signs of N-3 deficit in Alzheimer and Parkinson Disease, where maximum change involves the primary sites: olfactory cortex and the hippocampus. The olfactory agnosia observed in schizophrenia supports an N-3 deficit as does a reduction of key ologodendrocyte- and myelin-related genes in this disorder and affective disorder, where a rise in dementia accords with a deficit of N-3 also in this disorder.

N-3 normalizes cerebral excitability at all levels. That the two disorders are localized at the extremes of excitability, is supported by their opposing treatments: convulsant neuroleptics and anti-epileptic antidepressants.

An adequate N-3 diet will probably prevent most psychotic episodes and prove that neurodegenerative disorder with dementia is also to a large extent not only preventable but avoidable.