Nutrition and the brain
The most energy-hungry organ in the body, which depends on a continuous supply of glucose or ketone bodies, plus structural fats and the precursors of neurotransmitters.
The brain makes up about 2% of body weight but uses close to 20% of your energy at rest. It has no reserves of its own, so its supply has to be continuous, which is why cognitive function is sensitive to changes in blood sugar.
Its usual fuel is glucose, but not exclusively: during prolonged fasting or a ketogenic diet, the brain switches to ketone bodies, which can cover a large share of its needs. This metabolic flexibility is an ancient adaptation, not a pathological state.
It is also the fattiest organ in the body, with fat making up around 60% of its dry weight. Long-chain omega-3 fatty acids, DHA in particular, form part of the very structure of neuronal membranes. Phospholipids and choline contribute to membrane structure and to the synthesis of acetylcholine, which is involved in memory.
Finally, food supplies the precursors of neurotransmitters: tryptophan for serotonin and tyrosine for dopamine, with B vitamins as cofactors. This is one of the biological bases of the link between diet and mood. The link is real, but it does not justify the promises of “antidepressant foods” that you sometimes read about.