Neurotransmitters in the gut vs brain: what’s the difference?

Ever heard the phrase “gut feeling“? It turns out, there’s real science behind it. Following another INSPIRING presentation by Amrita Vijay – our brilliant Lead Scientific Advisor – I just had to dive deeper into this topic.

Your gut is packed with neurons that communicate using neurotransmitters, just like your brain. This is thanks to the enteric nervous system (AKA your “second brain”), which is part of the gastrointestinal tract. Your enteric nervous system works independently of the central nervous system, but the two are deeply connected.¹

Alongside neurotransmitter production, your gut microbes break down food and release enzymes that support digestion and nutrient absorption.

Even though both systems often use the same chemical messengers, the gut and the brain tell very different stories – one about digestion and the other about mood, memory, and more. These two communication hubs use neurotransmitters in uniquely clever ways. They are as distinct as they are interconnected.

1. Serotonin

It’s true – 90% of your body’s serotonin is produced in the gut. Often dubbed “the happy hormone”, serotonin plays a key role in mood regulation. But does that mean your happiness is solely dependent on your gut’s serotonin production? The answer isn’t quite so straightforward…

In the gut, serotonin helps regulate digestion and coordinates gut motility, ensuring food moves smoothly through the digestive tract. In the brain, however, serotonin influences mood, sleep, and appetite.

Interestingly, the serotonin produced in your gut can’t cross the blood-brain barrier. Your gut still plays a key role in supporting your brain’s serotonin levels, though. How? By helping your body absorb tryptophan, an essential amino acid you get from protein-rich foods like eggs, poultry, tofu, and seeds.

Certain gut bacteria can metabolise tryptophan into compounds that influence serotonin production in the brain.²³ These compounds, or microbial metabolites, can influence how the brain regulates mood. The serotonin made in the gut stays local, helping with digestion and gut motility. However, the availability of tryptophan (and how it’s processed in the gut) helps determine how much serotonin your brain can produce.⁴

So, a healthy gut microbiome doesn’t just help you digest food – it influences the very building blocks your brain needs for mood, sleep, and emotional wellbeing. This reinforces the deep, two-way connection between your gut and your mind. Read more in How is your mental wellness connected to your gut?.

2. Dopamine

Known for driving pleasure, focus, and motivation, dopamine plays a key role in how you experience rewards and form habits. While it’s often associated with the brain, 50% of dopamine is produced by neurons in your gut. In the digestive system, dopamine helps regulate the secretion of gastric juices and blood flow, playing a vital role in gut function.

Just as with serotonin, your gut plays a key role in absorbing and processing the building blocks for dopamine. The amino acid tyrosine, which we get from protein-rich foods, is absorbed via the gut and later converted into dopamine – first in the body and then in specific brain regions. There, these precursors are transformed into the dopamine that fuels your pleasure and reward systems. This intricate connection raises an intriguing question: how much of your motivation and mood is influenced by the health of your microbiome?

3. GABA

Known as your body’s natural “chill pill” or “zen neurotransmitter”. GABA (gamma-aminobutyric acid) is the brain’s main inhibitory messenger. It helps calm the nervous system, reduce stress, and promote relaxation. As you may have guessed by now, your gut plays a significant role in GABA production too. Certain gut bacteria, such as Lactobacillus and Bifidobacterium species, produce GABA.⁵ These beneficial probiotic species can help support a healthy balance of gut flora. This is particularly important when addressing dysbiosis (an imbalance of microbial populations in the gut). GABA helps keep your digestive processes in balance. It calms your digestive processes and prevents them from becoming overactive.

Even though GABA itself doesn’t cross the blood-brain barrier, it still influences brain function. How? Through the gut-brain axis – a two-way communication network linking gut activity to brain function. Gut-produced GABA can signal the brain via two key pathways:

Vagus nerve signalling: The GABA produced in your gut can stimulate the vagus nerve (the main highway between your gut and brain).⁶ This indirect communication may influence mood and stress responses.
Immune system modulation: Gut-derived GABA can interact with the immune system, affecting immune signalling. Changes here can impact brain function and behaviour due to the immune system’s role in neuroinflammation and mood regulation.

While researchers are still unravelling all the details, studies suggest that a healthy microbiome supports effective GABA signalling. This may help improve stress resilience, sleep, and even anxiety management.

4. Norepinephrine (Noradrenaline)

Norepinephrine is your “fight or flight” responder. When you encounter stress or a perceived threat, norepinephrine is released to boost alertness, ramp up your heart rate, and get you ready to respond quickly. But its role isn’t confined to the brain. In the gut, norepinephrine helps regulate motility and digestion, much like serotonin and dopamine. This underscores the intricate connection between your nervous system and your digestive tract.

Continuing the theme of gut-brain interplay, the gut also supplies the raw materials needed for norepinephrine production. The essential amino acid tyrosine, modulated by your gut microbiota, serves as a precursor for dopamine. Once tyrosine passes into the brain, it is converted into dopamine, and in certain neurons, dopamine is further transformed into norepinephrine. This process occurs in neuronal cells both in the brain and the gut. So, a healthy gut not only influences immediate digestive functions but also indirectly supports the synthesis of key neurotransmitters that govern your stress responses and overall alertness.

This is just one more reason why gut health is such an exciting area of neuroscience – the same neurotransmitters used in your brain are also produced, received, and activated by receptors in your gut, affecting everything from digestion to stress.

So, what does this all mean for you?

Your gut and brain are in constant conversation. They use the same chemical messengers to talk about very different things. Whether it’s serotonin steering your digestion, dopamine guiding your food choices, or GABA helping you chill out after a long day, your gut is more involved in your mood and mental health than you might think.

Disruptions in the gut microbiome (known as dysbiosis) have been linked to issues like irritable bowel syndrome (IBS), anxiety, and low mood, further highlighting how important your gut health is to your overall wellbeing.⁷

The key to supporting this system? Nourishing your gut with a diverse, fibre-rich diet, plenty of colourful plants, and fermented foods that support a thriving microbiome. To make this even easier, include a daily gut-healthy smoothie in your morning routine, combining kefir, Complete Prebiotic and Pure Fish Collagen – your full Gut Health Protocol in one easy drink. Because when your gut microbes are well-fed and happy, they send the right messages to your brain and beyond.

Trust your gut. It might just be the smartest thing you do today.

Check out How your gut microbiome is like a garden to further understand and enhance your health!

Any questions? Contact one of our Nutritional Therapists via live chat, weekdays from 8 am to 8 pm.