The Gut-Brain Connection: Why Your Stomach Affects Your Mood

The NURA Team
May 16
5 min read

You've felt it before. Nerves before a big moment – and suddenly your stomach is involved. A stressful week – and your digestion is off. An anxious day – and you can't quite explain why you feel heavy, foggy, off.

We tend to treat these as separate things. The mind is up there. The gut is down here. They're connected loosely, maybe, but they operate independently.

They don't.

The relationship between your gut and your brain is one of the more fascinating – and underappreciated – areas of current health research. And understanding it changes how you think about both mental clarity and physical wellbeing.

The Second Brain

Your gut has its own nervous system.

It's called the enteric nervous system, and it contains more than 500 million neurons –more than either the spinal cord or the peripheral nervous system. It can operate independently of the brain, regulating digestion, sensing the gut environment, and communicating with the rest of the body entirely on its own.

This is why scientists sometimes call it the "second brain." Not metaphorically. Structurally, functionally – your gut is doing a significant amount of neural work.

And it's in constant conversation with the brain upstairs.

What Is the Gut-Brain Axis?

The gut-brain axis is the name for the two-way communication network connecting your gut and your brain. It runs through the vagus nerve – the longest cranial nerve in the body, travelling from the brainstem all the way down to the abdomen – as well as through hormonal signals, immune pathways, and the metabolites produced by your gut bacteria.

The key word is two-way.

Your brain sends signals to your gut – which is why stress affects digestion, why anxiety can cause nausea, why emotional states show up physically in your stomach. You already knew this intuitively.

But your gut sends signals back to your brain just as constantly. What those signals say depends largely on the state of your gut microbiome. And this is the part most people haven't heard yet.

How Your Gut Bacteria Affect Your Mood

Your gut bacteria don't just digest food. They produce neuroactive compounds – chemicals that directly influence how your brain functions and how you feel.

Serotonin

Around 90% of your body's serotonin is produced in the gut, not the brain. Serotonin is the neurotransmitter most closely associated with mood regulation, feelings of wellbeing, and emotional stability. Gut bacteria play a direct role in its production. When microbial diversity declines – a state called gut dysbiosis – this production is affected.

GABA

Gamma-aminobutyric acid is the brain's primary inhibitory neurotransmitter. It reduces neuronal excitability and plays a key role in managing anxiety and stress responses. Certain gut bacteria produce GABA directly. Research suggests that imbalances in these bacterial populations may contribute to heightened anxiety.

Dopamine

Around 50% of the body's dopamine is produced in the gut. Dopamine is involved in motivation, reward, focus, and the feeling of pleasure. Your gut bacteria influence its production and availability.

Short-chain fatty acids

When gut bacteria ferment prebiotic fibre – the kind found in certain foods and functional ingredients – they produce short-chain fatty acids like butyrate. These compounds cross the blood-brain barrier, reduce neuroinflammation, and support cognitive function. You can read more about how prebiotic fibre feeds this process.

What Disrupts the Gut-Brain Axis?

The same things that cause gut dysbiosis also disrupt the gut-brain axis – because the two are inseparable.

Chronic stress is both a cause and an effect. Stress alters the composition of your gut microbiome. A disrupted microbiome amplifies stress signalling. The two reinforce each other in a loop that's easy to get stuck in and harder to break without intentionally addressing both ends.

Low-fibre diets reduce populations of the bacteria responsible for producing short-chain fatty acids and neurotransmitter precursors. Less fibre means less microbial activity means fewer neuroactive compounds being produced.

Poor sleep disrupts circadian rhythms that your gut bacteria follow. Sleep deprivation measurably alters microbial diversity, which then feeds back into mood regulation and cognitive clarity – which makes sleep harder. Another loop.

Antibiotics, while sometimes medically necessary, broadly reduce microbial diversity and can have lasting effects on the populations of bacteria involved in neurotransmitter production.

The Research Is Still Evolving — But the Signal Is Clear

It's worth being honest here: this is an active area of research, not settled science. The gut-brain connection is real and well-established. The specific mechanisms – exactly which bacteria, producing exactly which compounds, having exactly which effects – are still being mapped.

What the research consistently shows:

People with gut dysbiosis report higher rates of anxiety and low mood
Interventions that improve gut microbiome diversity – through diet, prebiotics, fermented foods – show measurable improvements in mood and cognitive function in multiple studies
The gut-brain axis is a genuine bidirectional pathway, not a metaphor

This doesn't mean your gut is the only explanation for how you feel mentally. It means it's one that deserves more attention than it typically gets.

What This Looks Like in Real Life

The gut-brain connection shows up subtly. You might notice:

A difficult week at work coinciding with digestive disruption
A period of poor eating followed by a stretch of low mood or mental fog that doesn't have an obvious emotional cause
Anxiety that sits in your stomach as much as your head
Better mental clarity on days when your digestion feels settled

These aren't random. They're the gut-brain axis doing exactly what it does.

How to Support Both Ends

Because the relationship is bidirectional, supporting the gut-brain axis means addressing both sides.

Feed your gut bacteria consistently

Prebiotic fibre is the raw material your gut bacteria use to produce short-chain fatty acids and support neurotransmitter production. A diet rich in diverse plant foods, prebiotic-containing ingredients, and fermented foods directly supports this process. Best prebiotic foods to add to your morning routine is a practical starting point if you're not sure where to begin.

Manage stress – and be consistent about it

Because stress and gut health reinforce each other, stress management isn't just good for your mind. It's good for your microbiome. Movement, sleep, daily rituals that create calm – these all have a downstream effect on gut bacterial populations.

Prioritise sleep

Your gut bacteria follow a circadian rhythm. Irregular sleep disrupts it. Even modest improvements in sleep consistency can have measurable effects on microbial diversity over time.

Build a morning ritual that supports both

One of the reasons we think about NURA as a daily ritual rather than just a drink is because of the compound effect of consistency. Matcha's L-theanine supports calm, focused energy — which affects how you handle stress — while the prebiotic element feeds the gut bacteria involved in neurotransmitter production. You can read more about what L-theanine actually does. Two things, working together, every morning.

The Bottom Line

Your gut and your brain are not separate systems running parallel lives. They are in constant conversation — through nerves, hormones, immune signals, and the metabolic activity of trillions of microorganisms that respond directly to what you feed them.

The way you feel mentally is, in part, a reflection of what's happening in your gut. And the state of your gut is, in part, a reflection of how you're managing stress, sleep, and what you're eating every day.

Understanding that relationship doesn't add complexity. It simplifies things. Because it means that taking care of your gut is also, genuinely, taking care of your mind.