The Gut–Brain Axis — How Your Gut and Brain Communicate
Have you ever noticed your gut reacting before you’ve consciously had time to think?
Perhaps your stomach tightens before an important meeting.
You suddenly need the toilet while waiting to board a flight.
Or you’re getting ready to leave the house and your gut seems to know you’re apprehensive before you’ve even put that feeling into words.
Experiences like these are not unusual.
And they are not evidence that digestive symptoms are “all in your head”.
They are everyday examples of something happening inside all of us, all of the time:
your gut and brain are continuously exchanging and responding to information.
The biological communication system that makes this possible is known as the gut–brain axis. [1,2]
If you live with IBS, understanding that system can change the way you make sense of your symptoms.
Not because the gut–brain axis gives us one simple explanation for IBS.
It doesn’t.
But because it helps us move beyond the idea that digestive symptoms must originate either in the gut or in the brain.
The biology is much more interconnected than that.
Your gut does not work in isolation
We tend to think about digestion as something that happens largely by itself.
Food enters the digestive tract. It is broken down. Nutrients are absorbed. Waste eventually leaves the body.
But your gastrointestinal tract is not simply a length of plumbing.
Within its walls is an extensive network of neurons and supporting cells known as the enteric nervous system, or ENS. [3]
You may sometimes hear the ENS described as your “second brain”.
I use that expression carefully.
Your enteric nervous system does not think, reason or make decisions in the way your brain does.
But it is a remarkably sophisticated nervous system. It helps coordinate processes including gastrointestinal motility, secretion and local digestive reflexes, and it can carry out a considerable amount of this regulation without conscious involvement. [3]
You don't have to remember to move food through your intestines.
You don't have to consciously coordinate the muscular activity involved in digestion.
Much of it happens automatically.
But the ENS does not operate entirely on its own.
It interacts with nerves connecting the gastrointestinal tract with the brain and spinal cord, as well as with other biological systems involved in gut–brain communication. [2,3]
And that brings us to one of the most important things to understand about the gut–brain axis.
Communication goes both ways
The brain can influence the gut.
The gut can influence the brain.
That sounds simple, but it has important implications.
The relationship is still sometimes talked about mainly in one direction:
something happens psychologically — perhaps nervousness, worry or fear — and the gut reacts.
Most of us recognise that experience.
Think about the “butterflies” you may feel before speaking in public.
Those sensations aren't evidence that something has suddenly gone wrong with your digestive tract. They are an example of activity in the brain and nervous system influencing gastrointestinal sensation and function.
But communication also travels in the other direction.
Sensory information from the gastrointestinal tract continually reaches the central nervous system — the brain and spinal cord. Much of that information never enters conscious awareness. [2,3]
And that is exactly as it should be.
You wouldn't want to spend your day consciously monitoring every contraction, movement or change taking place inside your digestive system.
So the gut–brain axis is much more than a pathway through which “emotions affect digestion”.
It is a bidirectional biological communication network. [1–3]
The vagus nerve matters — but it isn't the gut–brain axis
You may already have heard of the vagus nerve.
It has become something of a celebrity in the wellness world.
And it is important.
The vagus provides one of the major neural routes connecting the brain with internal organs, including much of the gastrointestinal tract.
But it is only one route within a much larger system.
The gut–brain axis also involves the enteric nervous system, other autonomic and spinal pathways, the brain and spinal cord, and non-neural routes involving hormonal, immune and microbial signalling. [2,3]
We’ll look more closely at those different routes in Article 3.
For now, the important point is that the gut–brain axis isn't one telephone wire connecting two separate organs.
It is a network.
Information can travel through different biological routes and in both directions.
Why does this matter in IBS?
In Article 1, we looked at why IBS is classified as a disorder of gut–brain interaction, or DGBI.
The current Rome V framework describes DGBIs in terms of combinations of processes involving gastrointestinal motility, visceral sensitivity, mucosal and immune function, the gut microbiota and central nervous system processing. [1]
Recent reviews of IBS pathophysiology describe an equally complex picture. Research has identified potential peripheral mechanisms within the gastrointestinal system as well as central mechanisms involving the nervous system, and these processes can interact through the gut–brain axis. [2]
In other words, IBS is not simply a problem with a bowel working in isolation.
But neither is it simply a psychological problem.
People with IBS experience very real physical symptoms — including abdominal pain, bloating, constipation, diarrhoea, urgency and changes in bowel function.
And those symptoms are not necessarily explained by the kinds of structural abnormalities that routine investigations are designed to detect.
That does not mean nothing biological is happening.
IBS can involve changes in processes such as gastrointestinal motility, visceral sensitivity, mucosal and immune activity, the gut microbiome and the way gut-related sensory information is processed by the central nervous system. [1,2]
Significant symptoms can therefore arise from changes in how gastrointestinal and nervous-system processes are functioning even when routine investigations do not reveal a structural disease that explains them.
This is why I frequently use one simple phrase in my clinical work:
gut AND brain — not gut OR brain.
That distinction matters.
What do we actually mean by “communication”?
I sometimes describe IBS to clients as involving altered communication between the gut and brain.
That's a useful starting point.
But I don't want you to imagine that the gut is literally sending the wrong message down a faulty wire.
The biology is more sophisticated than that.
When scientists talk about gut–brain interaction, they are talking about information being detected, transmitted, processed and responded to across an interconnected biological system. [1–3]
Our nervous system is continually dealing with information from both inside and outside the body.
Most internal digestive activity can remain in the background.
That filtering is useful.
Imagine consciously noticing every small stretch of the bowel, every muscular contraction or every movement of gas and fluid after a meal.
Life would become difficult very quickly.
In IBS, differences can occur in processes such as gut motility, visceral sensitivity and the central processing of gut-related sensory information. [1,2]
That does not make the symptoms imaginary.
And it does not mean the brain is inventing them.
The processing of physical information by the nervous system is itself a biological process.
Think of a conversation rather than a broken machine
As an analogy, it can be useful to think of a conversation rather than a broken machine.
What one person says influences how the other responds.
That response influences what happens next.
The conversation develops through feedback.
Gut–brain communication has that same broad quality — although, of course, your gut and brain are not literally exchanging words.
Activity in the gastrointestinal system can influence activity elsewhere in the system.
Responses from the brain and nervous system can then influence gastrointestinal activity.
That activity generates further information.
It is an ongoing feedback process. [1–3]
This is very different from imagining the bowel as a broken machine sitting underneath a brain that has nothing to do with it.
But it is equally different from imagining the gut simply following instructions sent down from the brain.
They are parts of one continuously interacting biological system.
That does not tell us why every individual develops IBS.
Nor does it mean exactly the same processes are involved in every person.
Two people can meet the same diagnostic criteria for IBS while having different symptom patterns and different combinations of contributing mechanisms. [1,2]
The gut–brain axis gives us a framework for understanding how that complexity is possible.
Why this can be good news
When people first hear that IBS involves the brain and nervous system as well as the gastrointestinal tract, some understandably become wary.
Especially if they have previously felt dismissed.
So I want to make the implication very clear.
Involvement of the brain and nervous system gives us more potential treatment routes — not less legitimacy.
IBS care can work with different parts of the system.
Dietary approaches may be appropriate for some people.
Medication may have an important role.
And for some people, brain–gut behaviour therapies, such as IBS-specific Cognitive Behavioural Therapy or Gut-Directed Hypnotherapy, may also be appropriate. [4]
These approaches do not have to compete with one another.
They can work through different therapeutic routes and can be appropriate for different symptom patterns, contributing factors and individual needs.
That is one reason multidisciplinary care can make sense in a disorder involving an interacting biological system. [1,4]
The useful question isn't necessarily:
“Is my IBS coming from my gut or my brain?”
A better question may be:
“What might be contributing to my symptoms, and which parts of this system can we usefully influence?”
Where does Gut-Directed Hypnotherapy fit?
This is where understanding the gut–brain axis begins to become clinically useful.
If the brain and gastrointestinal system influence one another, it becomes biologically plausible that an intervention working through attention, learning, expectation and other nervous-system processes might also influence the experience of gastrointestinal symptoms.
This idea forms part of the rationale for brain–gut behaviour therapies, including Gut-Directed Hypnotherapy. [4]
That gives us a biologically plausible therapeutic point of entry.
It does not mean we have identified one specific gut–brain pathway through which GDH works.
We haven't.
And that is an important distinction.
The mechanisms through which Gut-Directed Hypnotherapy may influence IBS symptoms are still being investigated.
We'll come back to that in Article 3.
Because before asking how GDH might influence this system, there is another question we need to answer.
So what information is actually being communicated?
If there is one idea I would like you to take from this article, it is this:
Your gut and brain are not separate systems that occasionally interfere with one another. They continuously exchange and respond to information as part of normal human physiology.
In IBS, aspects of that interaction can function differently. [1,2]
Understanding that helps us move beyond the old argument about whether symptoms are coming from the gut or the brain.
But it raises another question.
If your gut and brain are communicating throughout the day:
what information is actually travelling between them?
What is the gastrointestinal system telling the brain?
What information travels in the other direction?
Where do nerves, hormones, immune signalling and the gut microbiome fit?
And what happens when the way that information is detected, processed or responded to changes?
That's where we're heading in Article 3.
If you want to learn more about Gut-Directed Hypnotherapy and my Gut-Brain Recalibration GDH Programme - head over to that page
References & further reading
1. Drossman DA, Chang L, Tack J. Disorders of Gut-Brain Interaction and the Rome V Process. Gastroenterology. 2026;170(6):1083–1098. doi:10.1053/j.gastro.2026.02.014.
2. Nasser Y, Shin A, Ford AC, Camilleri M, Black CJ. Pathophysiology of irritable bowel syndrome. The Lancet Gastroenterology & Hepatology. 2026. doi:10.1016/S2468-1253(26)00148-2.
3. Sharkey KA, Mawe GM. The enteric nervous system. Physiological Reviews. 2023;103(2):1487–1564. doi:10.1152/physrev.00018.2022.
4. Keefer L, Ballou SK, Drossman DA, Ringstrom G, Elsenbruch S, Ljótsson B. A Rome Working Team Report on Brain-Gut Behavior Therapies for Disorders of Gut-Brain Interaction. Gastroenterology. 2022;162(1):300–315. doi:10.1053/j.gastro.2021.09.015.