There are now five placebo-controlled trials of EPA in the treatment in schizophrenia, and four of these have given positive or partly positive findings. A cross-national ecological analysis of international variations in outcome of schizophrenia in relation to national dietary practices, showed that high consumption of sugar and of saturated fat is associated with a worse long-term outcome of schizophrenia.

It is known that a high sugar, high fat diet leads to reduced brain expression of brain-derived neurotrophic factor (BDNF) which is responsible for maintaining the outgrowth of dendrites.

Low brain BDNF levels also lead to insulin resistance which occurs in schizophrenia and is associated with diseases of the metabolic syndrome.

It appears that the same dietary factors which are associated with the metabolic syndrome, including high saturated fat, high glycaemic load, and low omega-3 PUFA, may also be detrimental to the symptoms of schizophrenia, possibly through a common mechanism involving BDNF.