Mind the gut:
your gut, the bacteria that live in it, and how they communicate with your brain 

It’s not uncommon to feel you have “butterflies in your stomach” before a big presentation, or to get stomach cramps when you are stressed - but have you ever wondered why this happens, or why those sayings exist? You might be surprised to know there is a lot of science behind these peculiar physical manifestations of your internal emotional state, particularly around the connection between your gut, brain and mood regulation.

The microscopic civilization that exists inside you

Picture your gut as a bustling metropolis, home to trillions of microorganisms collectively known as the gut microbiome. Consisting of bacteria, viruses and fungi - there is an entire ecosystem that lives inside you. In fact, you are more bacteria than you are human, with bacterial cells closely outnumbering human cells. While that may sound like a bad thing, these organisms actually play a key role in overall health, influencing everything from digestion and immune function. More research is also starting to show its significant role in shaping our mood and mental health.

How does your gut and brain communicate?

The Gut-Brain Axis
Your gut and brain communicate through an extensive and sophisticated network known as the gut-brain axis. Imagine a bidirectional highway that links your central nervous system (CNS) with your enteric nervous system (ENS). It has such an impact on your overall functioning that it’s often called “the second brain”. It consists of a complex network of neurotransmitters (chemical messengers), chemicals and microbes, designed to carry important information and instructions.

Whilst there is still a lot of research to be done on the exact mechanism of how the gut-brain axis works, there are a few well established theories including:

The Vagus Nerve
A large nerve which runs from your brain to your colon, and has the widest distribution in your body. It carries signals from the gut to your brain, like a telephone line. Both human and animal studies have also shown that the gut microbiome, and the substances it produces, can influence mood through this channel.

These are chemical messengers that carry important information affecting the function of various organs in your body. They are produced in both your brain and gut, and your gut microbiome can influence this production. Serotonin, for instance, a neurotransmitter often associated with mood, is predominantly produced in the gut. Whilst a lot of it does not cross the gut barrier to travel up to your brain itself, it can locally activate nerve endings that are directly connected to the central nerve system. As certain bacteria influence serotonins production, an imbalance in the gut microbiome could potentially lead to dysregulated levels, with consequences on mood and emotional regulation.

Gut Microbiome and Metabolites
Your gut bacteria work hard to maintain your bodily functions without you even realising. They can affect:
- How well you absorb nutrients from the food and drinks you consume.
- The release of hormones which can alter various pathways, such as the stress response pathway.
- The activation of your immune response which helps protect you against illness.

Gut Dysbiosis and Mental Health

There’s no doubt the gut and brain are intrinsically linked and in constant communication with each other, so it makes sense to believe that the health of your gut, and the bacteria who live in it, impact the health of your brain.

Increasing research has shown that there is a link between an imbalanced microbiome (more commonly known as “gut dysbiosis“, and risk of developing mental health conditions. This imbalance can compromise the protective barrier function of the gut, allowing harmful substances to leak into the bloodstream, triggering an inflammatory response. Whilst inflammation is a natural response to injury or infection, it can become problematic when it becomes chronic.

Bottom line

The good news is that we are now exploring possible ways to restore gut microbiota, such as through dietary interventions, and results are looking hopeful. By prioritising gut health through a balanced diet, we can potentially mitigate the risk of chronic inflammation. So whilst it’s not a novel, sexy new drug on the market, could food be the best, most cost-effective preventative medicine for mental health? There’s a good chance. 
If you are keen to know more about what dietary interventions we are referring to, stay tuned for another article coming up next.All in all, it’s fairly safe to assume - happy gut, happy mind.

Written by Dr. Julia Craggs, February 2024


Bifidobacterium: a probiotic for the prevention and treatment of depression - PMC (nih.gov)

Gut dysbiosis in severe mental illness and chronic fatigue: a novel trans-diagnostic construct? A systematic review and meta-analysis | Molecular Psychiatry (nature.com)

"Your Gut Knows" podcast by SANNO

Check our Your Gut Knows podcast episodes related to this article: IBS & Project Discovery

IBS & Project Discovery

Guest: Dr. Javier Santos,
senior gastroenterologist