The Gut Has a Brain Too

The vagus nerve, the microbiome, and why the bacteria in your gut affect how your mind feels  

There are more nerve cells in your gut than in your entire spinal cord. 

This is not a metaphor or a wellness approximation. It's an anatomical fact. The enteric nervous system — the network of nerve cells embedded in the lining of the digestive tract — contains somewhere between 200 and 600 million neurons. It is sophisticated enough to operate independently of the brain, to sense and respond to its environment, and to communicate bidirectionally with the brain through a dedicated neural highway called the vagus nerve. 

The gut is not a passive digestive tube. It is an active, communicating system with a direct line to the organ you think with.  

This is why Lactobacillus rhamnosus — a specific probiotic strain — is in a cognitive formula. Not as an afterthought. Not as a trend. Because the gut-brain connection is real, it is substantiated, and the bacteria living in your gut are part of it.  

The vagus nerve: the physical connection  

The vagus nerve is the longest cranial nerve in the body. It runs from the brainstem down through the neck, chest, and into the abdomen, connecting the brain to the heart, lungs, and digestive system.  

What makes the vagus nerve unusual is that it carries signals in both directions — and approximately 80% of its fibres carry signals from the body to the brain, not the other way around. The gut is primarily talking to the brain, not listening to it.  

What it communicates includes information about the state of the digestive system, immune activity, and the composition of the gut microbiome. The brain uses this information to regulate mood, stress response, appetite, and a notable portion of what we experience as general mental wellbeing.  

This is the anatomical basis of the gut-brain axis. Not a theory — a physical nerve, carrying signals, in both directions, all day.  

Where serotonin is made  

Around 90–95% of the body's serotonin is produced in the gut.  

This is one of the more counterintuitive facts in neuroscience, given how consistently serotonin is discussed as a brain chemical. It is a brain chemical — but it's largely made elsewhere.  The gut produces it and its signals are passed to the vagus nerve and onwards to the brain — the gut's serotonin doesn't cross into the brain directly, instead it interacts with the brain's own regulatory systems — systems that are involved in mood, sleep, and the general sense of mental wellbeing.  

Gut health and the feeling of emotional stability are connected through this pathway in ways that are only beginning to be fully understood.  

The microbiome: what is it and does it matter?  

The gut microbiome is a community of trillions of microorganisms — bacteria, fungi, viruses — that live in our digestive tracts. That may surprise you, it may even shock you. But don't worry, we all have a gut microbiome. It's not only normal, it's essential. In a healthy gut, this community is very diverse, balanced, and actively involved in several processes which go beyond the digestion of food and drink. 

Our microbiome also contributes to the production of compounds that our brains rely on. It can have a significant influence on the body's inflammatory response — and low-grade inflammation is increasingly associated with changes in mood, mental clarity, and cognitive function. It maintains the integrity of the lining of the gut, which acts as a barrier controlling what enters the bloodstream. 

The balance of the microbiome is fairly robust, but it can become disrupted. Antibiotics can kill off helpful gut bacteria alongside the pathogenic bacteria that they are being used to control. In addition, chronic stress, poor diet, or illness can all shift the balance. Because of the gut-brain connection, any of these disruptions to the microbiome may contribute to experiences that feel cognitive or emotional. 

→ The enteric nervous system  

200–600 million nerve cells in the gut lining. Operates independently and communicates bidirectionally with the brain.  

→ The vagus nerve  

The physical connection between gut and brain. 80% of its fibres carry signals from the body to the brain, not the reverse.  

→ Serotonin  

90–95% is produced in the gut. Gut serotonin signals influence the brain's regulatory systems via the vagus nerve.  

→ The microbiome  

The name given to the trillions of microorganisms that live in a healthy gut and which together contribute to compound production, inflammatory regulation, and gut barrier integrity — all of which can have downstream effects on cognitive and emotional experience.  

Lactobacillus rhamnosus: why this strain specifically? 

Not all probiotic strains of live bacteria are equivalent, and not all are relevant to the gut-brain connection. L. rhamnosus is one of the most studied strains in the specific context of the gut-brain axis — not just normal gut health in general.  

Research into L. rhamnosus has examined its effects on the gut-brain communication system, including its influence on the pathways that are involved in both stress response and the regulation of mood. More research is ongoing, and the mechanisms are not yet fully characterised. But what we can say, is the evidence base for this specific strain, in this specific context, is more substantive than for most probiotic strains, which is why it's in the formula at all. 

It is worth noting that it is not in get dopa as a general digestive support, although there may be side benefits there. It's there because the gut-brain axis is an important and legitimate aspect of cognitive nutrition.  

get dopa contains L. rhamnosus at 5 billion CFU per serving. CFU — colony-forming units — is the measure of live, active bacteria. It is included because this strain has been widely studied in the context of gut-brain communication, and 5 billion CFU is consistent with doses used in the published research, rather than being a token amount that's included for label appeal. 

What this means for the formula as a whole 

The gut-brain axis article is the penultimate in this series, and it's a useful place to step back and look at the formula as a whole.  

get dopa contains 16 ingredients. The six articles in this series have covered the amino acids that provide raw materials for the brain's processes, the B vitamins that facilitate those processes in active, bioavailable forms, the ingredients that support the brain over the long term through consistent nutritional provision, those relevant to the brain during periods of hormonal change, and now the gut-brain connection.  

These are not sixteen ingredients selected to make an impressive list. Each one has a specific role. Each one was chosen for a reason — a formulation decision that adds cost and complexity but provides something the category typically doesn't.  

The case for the formula isn't that it contains everything. It's that everything in it has a reason to be there. 

KEY TAKEAWAYS 

• The enteric nervous system contains somewhere between 200–600 million nerve cells and operates independently of the brain, communicating in both directions, via the vagus nerve.  
• Approximately 90–95% of the body's entire serotonin is produced in the gut. Our gut health and mental stability are connected through this pathway.  
• The vagus nerve carries approximately 80% of its signals from the body to the brain. It is a two-way channel, but the gut is primarily communicating with the brain, not the reverse.  
• The gut microbiome influences the production of compounds, our inflammatory response, and gut barrier integrity — all these can have downstream effects on cognitive and emotional experience.  
• Lactobacillus rhamnosus is a specific bacterial strain that has been studied in the context of the gut-brain axis. It is included in get dopa at a deliberately chosen level of 5 billion CFU — this strain has been studied in this context, the dose is directly comparable with those used in research.  
• The gut-brain axis is one of the systems the get dopa formula addresses — a deliberate formulation decision, not an add-on. 
  
  

NEXT IN THE SERIES

Part six of our six-part series looks at why the brain can feel different during hormonal changes. Specifically: the biological basis behind the focus, mood and motivation shifts many women experience during perimenopause and menopause, and which ingredients in the get dopa formula are relevant to that picture.