Microbiome and Mood

November 18th, 2019 | Posted in Info

The gut microbiome is a complex ecosystem of organisms comprising bacteria, yeasts, fungi, viruses and protozoans that live in our digestive system. These organisms are vital for breaking down food and toxins, making vitamins and playing a role in our immune systems.
More recently it has become clear that the gut microbiota have an important influence over brain development, behaviour and mood.

Additionally, there are various molecules made by these microbes that may play a role in mood and behaviour. These include neurotransmitters, short-chain fatty acids, bile acids, choline metabolites, lactate and vitamins (1).It is even thought that the gut microbiome might be as influential as our genes when it comes to our health and happiness.

The Vagus Nerve and Gut Brain Communication

The longest nerve in the body is the vagus nerve. It runs from the base of the brain to the intestines. It is thought to carry messages back and forth between the gut and the brain. The gut microbiome makes neurotransmitters and sends them to the brain which can then affect our mood.

The communication system between the gut and the brain appears to be a two way street in that alterations in the populations of specific organisms in the gut might contribute to depression and depressive states might change the make up of the microbiome (2).
Scientists now hope that it may one day be possible to diagnose some brain diseases and mental health problems by analysing gut bacteria, and treating them with specific bacteria.

Diversity of Diet = Diversity of Gut Organisms

The diversity of the gut microbiome appears to be strongly associated with mood-related behaviours, including major depressive disorder. One of the findings from the American Gut Project is that eating more than 30 different plant foods each week appears to increase the diversity of bacteria in the gut compared to eating 10 or fewer different plant foods (3). So, eating a wide range of plant foods every week could be one of the easiest ways of improving your mental health. Plant foods include fruit, vegetables, nuts, seeds, grains, pulses, sea vegetables, herbs and spices.


It’s possible that pre and probiotic formulations and fermented food could be used in the treatment of mental health disorders. These are being referred to as “psychobiotics” – a type of probiotic, that may have a positive effect on the mind.

Fermented foods that are rich in pre and probiotics include:

  • Fermented vegetables – such as sauerkraut and kimchi
  • Fermented milk products – such as yoghurt, kefir, cheese. Yoghurt and kefir can be made with soya milk or coconut milk.
  • Fermented soy beans – such as tempeh, miso, natto and tamari
  • Kombucha – a drink made from fermented tea
  • Apple cider vinegar
  • Sour dough bread
  • Water kefir

See the blog post on Diets for Depression for more ideas about which foods and diets can help improve your mood.

Beyond the Brain

As well as being implicated in mental health, the gut microbiome may influence our athleticism, weight, immune function, inflammation, allergies, metabolism and appetite.

Plants, Ferments and Brain Health

The gut microbiome is hugely important for many aspects of mental and physical health. Two of the best things you can do for your body are to eat a wide range of plant based foods and to include small amounts of fermented food daily.



  1. 1. Microb Cell. 2019 Sep 27;6(10):454-481. Gut microbial metabolites in depression: understanding the biochemical mechanisms. Caspani G, Kennedy S et al.
  2. 2. Rev Neurosci. 2018 Aug 28;29(6):629-643. Gut microbiome and depression: what we know and what we need to know. Winter G, Hart RA et al.
  3. 3. Msystems, 2018; 3 (3): e00031-18. American Gut: an Open Platform for Citizen Science Microbiome Research. Mcdonald D et al