Gut Feelings: How Our Gut and Brain Communicate

June 7, 2023

Our gut and brains are busy communicating 24/7, and for better or worse, these conversations play a significant role in our mental well-being. The good news is that by understanding how they communicate we can change the conversation – thereby giving our overall health a real boost. 

The secret could lie with some unlikely allies – the 100 trillion microbes in our gut. We live in a mutually beneficial relationship with these microbes; we give them shelter and food, and in return, they produce important molecules our bodies need.

Spearheading a small revolution in mental well-being, Professor Timothy G Dinan, at University College Cork and APC Microbiome Ireland, has spent the past two decades exploring the role of gut microbes in regulating brain function. He’s on a mission to share the evidence and show us how.

“While brain–gut communication has been a subject of investigation for decades, an exploration of gut microbes as a fundamental component within this context has only been addressed recently.”
Dinan, 2022

So, what is the gut-brain connection? 

The vast community of microbes in our gut – our gut microbiome – consist of mainly bacteria but also fungi, yeasts and viruses. The total weight of bacteria in our adult intestines is estimated at 1.5kg, and they produce hundreds of compounds, many of which influence our brain.

The main ways in which gut microbes communicate with our brain are through:

1. The vagus nerve

  • That long meandering nerve connecting the brain and the gut – is an important route of communication

2. Production of short chain fatty acids (SCFA)

  • Humans cannot produce SCFA (such as butyrate), but certain microbes do so by metabolising fibre 
  • SCFAs can enter the blood stream and travel to the brain 

3. Production of signalling molecules and neurotransmitters, such as:

  • Dopamine 
  • Noradrenaline
  • Gamma-aminobutyric acid (GABA)
  • Tryptophan

Certain microbes such as Bifidobacteria, can increase the blood levels of tryptophan, the building block for our ‘happy molecule’ serotonin. It is needed in steady supply because our because our brain cannot store it to any great extent.

Can imbalances in the gut microbiome cause anxiety and depression? 

There is increasing evidence that the gut microbiome is altered in depression.

Dysbiosis (an imbalance in the gut microbiome) and inflammation of the gut have been linked to several mental illnesses including anxiety and depression.

Studies show the gut microbiome of depressed people is less diverse than in healthy people. Incredibly, Dinan et al found that when transplanting gut microbiota from a depressed patient into a rat, there was a significant difference in the rat’s behaviour and they became “depressed-like”. Their immunological profile and the metabolism of tryptophan also changed. Rats who received faecal transplants from healthy people, showed no difference in behaviour.

Further evidence of the strong link between our gut and our brain shows that people with certain digestive disorders have a higher risk of depression and anxiety. Barandouzi et al found that the microbiome was significantly different in people with irritable bowel syndrome (IBS) and emotional distress compared to healthy people. 

For example, levels of the ‘happy molecule’ serotonin were positively associated with abundance of Proteobacteria, and norepinephrine positively correlated with Bacteroidetes, but negatively associated with Firmicutes phylum.

“It has become clear … that gut microbes play a fundamental role in regulating not just the brain, but the function of other organs as well”
– Dinan, 2022

Can we strengthen mental well-being by boosting our gut health? 

The good news is that, yes, by improving our gut health, we can boost physical health and mental well-being.

Just as cardiologists recommend a heart-friendly diet, psychiatrists should work with patients to optimise their diet alongside current standard of care, such as medications and Cognitive Behavioural Therapy (CBT).

One rule of thumb is that the more diverse the community of microbes is, the healthier we tend to be. 

We can achieve this through:

Boosting our diet

Eating a variety of:

  • Fruit
  • Vegetables
  • Nuts
  • Fish
  • Fermented foods (e.g., yoghurt, kefir, kombucha)


  • Pro-inflammatory, red meat
  • Processed foods 

Lowering stress 

Studies find that lowering stress e.g., through meditation can have a beneficial effect on the microbiome and reduce cortisol, the main stress hormone.

Taking probiotics 

Dinan et al coined the term ‘psychobiotic’ – bacteria which, when ingested in adequate amounts, had a positive mental health benefit.

They found that the probiotic Bifidobacterium longum reduced anxiety levels and cortisol.

The race is on to find probiotic treatments that target our microbiome and demonstrate positive effects on mental well-being.

In summary

Emerging research helps us understand the role of our gut microbiome in mental health and how we can take effective steps to look after it. The gut microbiome is looking increasingly like the foundation of well-being.    

And one day, hopefully soon, taking care of our microbiome and mental well-being will be as important and every-day as going to the gym!

About The Author

Berit Sund, MSc

Founder ACTA Medical and Creator of


How do gut microbes influence mental health? - Dinan - 2022 - Trends in Urology & Men's Health - Wiley Online Library

Anxiety might be alleviated by regulating gut bacteria | BMJ

How gut health affects mental health ( 

Stress, depression, diet, and the gut microbiota: human–bacteria interactions at the core of psychoneuroimmunology and nutrition - PMC (

Associations of neurotransmitters and the gut microbiome with emotional distress in mixed type of irritable bowel syndrome | Scientific Reports (

Alteration of faecal microbiota balance related to long-term deep meditation | General Psychiatry (