Written by: Brittani Kolasinski (BHSc - Nut, AdvDip Nut Med) 

For a number of years now depression has been thought of as a condition triggered by some ‘chemical imbalance’ within our brains – more specifically a deficiency of a neurotransmitter serotonin. However, more recently depression is now more understood of as a condition influenced by inflammation and closely connected to our immune system – and we now know that the majority of our immune cells are located within our gut (also where 97% of our serotonin is produced!).

Studies have found that depressed people have elevated levels of inflammatory proteins in plasma and cerebrospinal fluid, with increases of cytokines TNF-alpha, IL-6 and C-reactive protein.

Tryptophan is of importance to note - as an amino acid that is required for the synthesis of serotonin and melatonin. However, there is also a lesser known biochemical pathway for tryptophan and this is known as the kynurenine pathway. This kynurenine pathway accounts for about 99% of ingested tryptophan that isn’t used for protein synthesis (amino acids make up the structure of proteins within the body), and this pathway was first thought to be involved in the creation of a substance known as nicotinamide adenine dinucleotide (Davis & Liu, 2015)

…. (please stay with me through these biochemical terms – its really interesting stuff!)

The kynurenine pathway has been linked now with neurodegenerative disease, tumour proliferation, inflammation and depression! You see, when inflammation is present, more tryptophan goes into the kynurenine pathway to produce quinolinic acid and kynurenic acid, and not serotonin. Quinolinic acid and kynurenic acid are neuroactive and its believed that they contribute to behavioural changes experienced by individuals when inflammation is increased through exposure to stimuli like chronic stress, toxin exposure, diet or lifestyle. Common antidepressant medications (SSRIs) work by increasing the amount of tryptophan to serotonin, but also ignoring the effects of the inflammatory cytokines which have triggered the depression (Raison et al, 2010).

Factors that increase inflammation and increase risk and severity of depression

  • Inactivity

  • Reduced sleep

  • Social isolation

  • Obesity

  • Diet low in omega 3 fatty acids (anti-inflammatory fatty acids)

  • Low serum cholesterol

  • High sugar diet

  • Smoking

Interventions that reduce depressive symptoms have been reported to lower inflammatory and/or increase anti-inflammatory, immune-regulatory activity in the body and brain (Raison et al. 2010).

Apart from SSRI’s, there are a number of dietary interventions and lifestyle habits that can help to reduce inflammation, alleviate feelings of depression and help combat future occurrences of the condition…

Get in touch if you’d like to know more, I’d be happy to work with you as your health practitioner, using food as medicine and lifestyle modifications to have you happy and healthy.



Davis, I., & Liu, A. (2015). What is the tryptophan kynurenine pathway and why is it important to neurotherapy? Expert Review of Neurotherapeutics15(7), 719–721. http://doi.org/10.1586/14737175.2015.1049999

Raison, C. L., Dantzer, R., Kelley, K. W., Lawson, M. A., Woolwine, B. J., Vogt, G., ... & Miller, A. H. (2010). CSF concentrations of brain tryptophan and kynurenines during immune stimulation with IFN-α: relationship to CNS immune responses and depression. Molecular psychiatry15(4), 393.