Diet and mental health
A field of research on the links between diet, mood and cognitive function, with documented associations but mechanisms that are still only partly understood.
The link between diet and mental health has been the subject of active research for about twenty years. Observational studies show consistent associations between a Mediterranean-style diet and a lower prevalence of depressive symptoms, but association does not mean causation: eating habits go hand in hand with other lifestyle factors.
Three plausible mechanisms are being explored. Food supplies the precursors of neurotransmitters (tryptophan for serotonin, tyrosine for dopamine), with B vitamins as cofactors. It modulates low-grade inflammation, which is associated with mood disorders. Finally, the gut microbiome communicates with the brain via the gut-brain axis.
These real links do not make food a treatment. This is the limit that needs to be stated clearly: no food or supplement replaces psychological or drug treatment when it is indicated. Nutritional intervention trials in depression show modest effects, as a complement to follow-up care, never in its place.
Two points do command consensus and are worth knowing: a deficiency in vitamin B12, vitamin D or iron can cause fatigue and depressive symptoms, and can be corrected; and large blood sugar swings affect mood in the short term. Any lasting psychological distress should be seen by a health professional.