Depression is now the most widespread psychiatric diagnosis in the world. The standard treatment — antidepressants — works for roughly 40–60% of patients. For the remaining 40–60%, medication does not work, or works only partially. Why? Because depression is not a single disease — it is a syndrome with a range of biological causes.
How to read the numbers: Fact = a finding from research or biology · Term = a key term or marker worth knowing
Is made in the gut
Most of the body's serotonin is made by gut cells, where it regulates digestion; it does not cross into the brain, which makes its own. The gut influences mood indirectly via the gut–brain axis, so eating plenty of fibre and varied plant foods is worthwhile.
Reduces depression vs. medication
Large reviews suggest that for mild to moderate depression, exercise can be about as effective as standard treatment; the exact ratio varies between studies and should be read with caution. Treat exercise as a complement – never stop medication without your doctor.
Key to plasticity
BDNF is a protein that supports neuron growth and the formation of new connections – the brain's ability to learn and adapt. Regular aerobic exercise raises it most reliably, and quality sleep supports it too.
The inflammatory hypothesis of depression
Research over the past decade shows a strong link between chronic inflammation and depression. Inflammatory cytokines (IL-6, TNF-alpha) directly affect the metabolism of serotonin, dopamine and GABA. People with high inflammatory markers respond better to anti-inflammatory treatment than to antidepressants.
95% of serotonin is produced in the gut. The microbiome communicates with the brain via the vagus nerve, the immune system and hormones. A disrupted microbiome — dysbiosis — is consistently linked to depression and anxiety.
ADHD as a biological state
ADHD is not just "inattention". It is a neurological variation with measurable differences in dopamine signalling, prefrontal cortex structure and sleep architecture. The biohacking approach: optimise sleep, eliminate inflammatory foods, move (which raises BDNF and dopamine), and use breathing techniques.
