The Microbiome & the Brain


Human beings have a ‘second brain’ in the gut – a number of enteric cells, containing the same number of neurones as the brain of a cat, stretched out along the digestive tract. 

These cells are in direct communication with the brain, via the Vagus Nerve.  This communication is not one way either – the gut influences the brain and the brain responds. 

The gut bacteria produce a large number of neurotransmitters, which help and support the brain and mood:

  • 95% Serotonin (our happy brain chemical) is actually produced in the gut and then sent to the brain
  • Dopamine production is also largely reliant on our gut flora – dopamine is important for motivation
  • GABA (an anti-anxiety neurotransmitter) is also synthesised by good bacteria.

Therefore, the gut flora will have a huge impact on mood, motivation and behaviour.  If the bacteria involved in the production of these neurotransmitters were depleted, this could lead to increased levels of stress, anxiety and depression.  Furthermore, this appears to be something of a cycle – as stress and poor sleep are known to reduce the levels of good bacteria living in the gut. 

All of this means that good bacteria levels play a vital role in the management of stress, anxiety and depression.


In trials, it has been shown that supplementing the diet of depressed people with a combination of L. acidophillus, L. casei and Bifidobacteria bifidus significantly improved their mood and motivation.(1)  

L. rhamnosus has also been shown to have beneficial effects in the treatment of depression and anxiety.(2) 

Combining these bacteria with a B Vitamin complex – which can be used to support healthy mood and mental performance – could provide the missing piece of the puzzle for many people struggling with long term anxiety or depression issues. It could also be a key combination for stressed, busy people who are feeling fuzzy headed or forgetful.

Written by Jenny Logan DNMed. (Jenny is a Nutritional Therapist who has worked with clients in health foods stores and private clinics for over 20 years)


  1. The effects of probiotics on depressive symptoms in humans: a systematic review; Caroline J Wallace; Ann Gen Psychiatry 2017
  2. Ingestion of Lactobacillus strain regulates emotional behaviour and central GABA receptor expression in a mouse via the vagus nerve; Javier A Brails et al; Proc Natl Acid Sci USA; 2011




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