Irritable bowel syndrome and stress: the axis between the gut and the brain

Before a meeting in another building, she checks where the toilet is. Before a day out, she checks where she’ll be able to stop. In the morning she skips breakfast because “it’s safer that way”. At dinner with friends she orders something she doesn’t like, because she knows it won’t upset her. And when a colleague remarks in passing that she’s probably just stressed, she smiles and says nothing.

This is what life looks like for many people with irritable bowel syndrome. Invisible from the outside, but on the inside organised around the gut. And because stress really does play a part, people very quickly end up hearing a simplified message: “Calm down and it will pass.” As if the gut were just a mirror of poorly managed nerves.

It isn’t. In this post I will try to explain how the gut and the brain really are connected, why stress affects digestion — and why, even so, irritable bowel syndrome is not “purely psychological”.

What irritable bowel syndrome is

Irritable bowel syndrome (IBS) is a disorder of how the gut functions. Under the international Rome IV criteria it is defined by recurrent abdominal pain, on average at least one day a week over the past three months, associated with bowel movements, with a change in how often you go, or with a change in the form of the stool. For some people diarrhoea predominates, for others constipation, and for others the two alternate. Bloating, cramps and a feeling that the bowel hasn’t fully emptied are almost always part of the picture.

How common it is depends on how it is measured. A meta-analysis published by Lovell and Ford in 2012, using older criteria, estimated that around 11 per cent of people worldwide have it. A large global study by the Rome Foundation in 2021, using the stricter Rome IV criteria, counted around 4 per cent. The difference doesn’t mean one figure is wrong — it means many people have digestive problems, while fewer meet all of the strict criteria. It is more common in women than in men.

Importantly, IBS is a real disorder. The ICD-11 classification places it among conditions in which pain is a disease in its own right, and research shows measurable changes in gut motility, in the sensitivity of the gut wall and in how the brain processes signals from the abdomen. The fact that tests show no inflammation or damage doesn’t mean there is nothing there. I wrote more broadly about what the sentence “the tests are normal” means in the post “The tests are normal, but it still hurts”: what therapy knows about psychosomatics.

A doctor first — always

Before I talk about stress, something that isn’t up for negotiation. An IBS diagnosis is made by a doctor, and only after weighing up whether it could be something else. Similar problems can be caused by coeliac disease, inflammatory bowel disease (Crohn’s disease, ulcerative colitis), certain infections, thyroid disorders, bile acid malabsorption and also bowel cancer.

See a doctor without delay if you notice:

• blood in your stool or black stool,
• unexplained weight loss or anaemia,
• symptoms that wake you at night, or a fever,
• a change in bowel habits that first appeared after the age of 50,
• bowel cancer, coeliac disease or inflammatory bowel disease in your close family.

If you are between 50 and 74, also respond to the invitation to the Svit Programme, Slovenia’s screening programme for colorectal cancer. It isn’t meant for diagnosing IBS, but it is a simple way of ruling out something that mustn’t be missed.

And once more, because it matters: even when a doctor diagnoses IBS, that doesn’t mean the problems are “all in your head”. It means the head is part of the system that produces them — and so part of the way out of them, too.

The axis between the gut and the brain

The gut has its own nervous system. It is called the enteric nervous system and consists of hundreds of millions of neurons woven into the wall of the digestive tract. That is why it is sometimes called the “second brain”. It can regulate the contractions of the gut, the secretion of fluids and blood flow on its own — but it isn’t alone. It is in constant conversation with the brain.

That conversation runs along several pathways at once. The most important is the vagus nerve, which links the brainstem with almost all the internal organs; most of its fibres actually carry messages from the body to the brain, not the other way round. The second pathway is the stress hormones, among them cortisol, regulated by the axis between the hypothalamus, the pituitary and the adrenal glands. The third is the immune system, which is extremely dense in the gut. The fourth, much talked about in recent years, is the microorganisms in the gut, which influence the lining and the nerves through their metabolites.

That the conversation runs both ways isn’t just theory. In an Australian study, Koloski and colleagues followed people from the general population for twelve years. Those who were more anxious or low at the start were more likely to develop functional digestive disorders later. Those who had digestive problems at the start were more likely to develop anxiety or depression later. For some people, then, it began in the head, for others in the gut — and both pathways were real.

You can find more on this concept in the knowledge base under the gut–brain axis.

When the gut speaks too loudly

One of the most researched phenomena in IBS is visceral hypersensitivity. In experiments in which a small balloon was inflated in the bowel, people with IBS often felt discomfort or pain at a smaller degree of stretching than people without these problems. Their gut isn’t necessarily different — what is tuned differently is the system that receives and evaluates its signals.

This is very similar to what happens with chronic pain elsewhere in the body: the nervous system learns greater sensitivity, and the alarm goes off sooner than it should. I described in more detail how that amplifier gets turned up in the post Chronic pain and the nervous system: why pain stays after the wound has healed.

Interoception — the sensing of your body’s interior — contributes too. When attention has been focused on the abdomen for a long time, because it has so often been a source of trouble, perception sharpens. You notice every shift, every gurgle, every hint of a cramp. And each such signal triggers the question: “Is it back?” That question in itself puts the body on standby, which irritates the gut even further.

Stress doesn’t create IBS out of nothing — but it shapes it

I want to be precise here, because there are many misunderstandings. Stress is not the only cause of IBS. For many people it all began with an infection — after a stomach bug or food poisoning, some people develop long-lasting problems even though the infection is long gone. Research has shown that the risk of this is higher in people who were under more stress or more anxious at the time of the infection. The infection was the trigger, then, and stress influenced whether the system would find its way back into balance afterwards.

It is similar with diet, genetic make-up, the microbiota and hormones. All of these contribute. Stress is one piece of the puzzle — often an important one, never the only one.

What people with IBS describe very consistently is that their symptoms worsen during periods of tension: before exams, before important conversations, during a break-up, when moving house, under chronic stress at work. That isn’t a coincidence. When the nervous system is on standby, gut motility changes, the sensitivity of the gut wall increases, and the system’s ability to settle quickly after being stirred up decreases. I explained how this response starts in the brain, before you even think, in the post What happens in the brain during anxiety.

Fear of your own gut

With IBS a particular form of anxiety often develops that is directed precisely at digestion. Professionals call it gastrointestinal-specific anxiety. The person isn’t necessarily anxious in general. They are anxious about their gut: what will happen if it strikes on the bus, in a meeting, during a visit to the in-laws?

A whole range of safety behaviours grows out of this fear. Checking where the toilets are. Skipping meals. Narrowing the menu to a few “safe” foods. Cancelling trips, travel, socialising. Each of these behaviours brings relief in the short term — and each tells the nervous system in the long term that the gut is dangerous. It is the same loop we know from other forms of anxiety: avoidance helps you today and harms you tomorrow.

For some people the fear of symptoms is intertwined with a wider health anxiety; for others, narrowing the menu begins to resemble an eating disorder. If you notice your menu getting narrower and narrower without anyone advising it, it is worth talking to a doctor or a dietitian about it.

Shame, relationships and the shared table

Digestion isn’t something people like to talk about. You mention a painful knee without embarrassment, but many people can’t talk about diarrhoea, wind or constipation even with those closest to them. That is why IBS often remains a secret — and a secret you carry alone is an extra source of tension.

As a marriage and family therapist in training, I notice how deeply the gut can reach into relationships. It changes shared meals, which in many families are a central space of closeness. It changes travel, sex, visits to relatives. A partner sometimes doesn’t understand why plans have to be cancelled yet again and reads it as lack of interest. The person with IBS doesn’t know how to explain, because they’re ashamed — or because they’re afraid of hearing “you’re just stressed”.

It might sound like this (composed, not a real person):

“You’re not coming with us to my parents’ again?”
“I can’t. My stomach.”
“It’s always your stomach when we go to my parents’.”
“… Yes. Because there I can’t get away anywhere. And because your mum asks every time why I eat so little.”

Something important happened in this conversation: instead of “my stomach”, the truth came out. It wasn’t an excuse; it was distress with both a bodily and a relational side. In relational family therapy, in which I am training, this is exactly what we explore — how one person’s tension flows through family patterns, and how a relationship can become a place where the body loosens rather than clenches. When digestive problems are tangled up with low mood, read Depression and the body: pain, fatigue and digestion too.

What helps on the psychological side

Psychological treatments for IBS aren’t a last resort for when everything else has failed. They are part of the treatment recommended in the guidelines of gastroenterological societies — not because IBS is a psychological illness, but because they act on the axis between the gut and the brain.

In 2019 Ford and colleagues gathered research on psychological treatments for IBS in a large meta-analysis and found that cognitive behavioural therapy and gut-directed hypnotherapy are among the approaches with the best support. Hypnotherapy has an interesting history here: as early as 1984, Whorwell and colleagues reported in The Lancet on improvement in people with severe IBS for whom other treatment hadn’t helped. Since then the effect has been replicated in numerous studies.

What do these treatments do? They help you recognise the loop of fear and avoidance and gradually loosen it. They teach how the nervous system settles after being stirred up. They change your relationship with bodily signals — from “danger” to “unpleasant, but manageable”. And they open up space for what lies in the background: pressures at work, tensions in relationships, old patterns in which everything had to be held inside.

Simple techniques for calming the autonomic nervous system can help too, for example breathing with a longer out-breath. Not because breathing “fixes” the gut, but because a longer out-breath encourages vagal activity and with it a state in which digestion flows more easily.

Exercise: when it strikes

You can do this exercise when you feel the first cramp or discomfort in your abdomen but aren’t in a situation where you need to act immediately. It isn’t meant to stop the symptom, but to keep you from adding fear to the pain.

1. Name what is happening. Say to yourself: “I notice a cramp in my lower abdomen.” A description, not a prediction.
2. Place your palm on your abdomen and breathe slowly, so that the out-breath is roughly twice as long as the in-breath. Repeat five times.
3. Separate two scales. Rate from 0 to 10 how strong the discomfort in your abdomen is. Then rate separately how afraid you are. Do you notice them as two different things?
4. If it isn’t urgent, wait two minutes before doing anything — before going to check where the toilet is or cancelling your plan. Keep breathing in the meantime.
5. Write down what happened: whether the discomfort changed, whether the fear changed, and what you did next.

Often the fear lessens first during this exercise, and only then — sometimes — the discomfort. That is an important insight: it shows that these are two layers, and that you can influence one of them even when you can’t yet influence the other.

Where stress isn’t the answer

I want to be honest here, because the story of the gut–brain axis can quickly turn into a new oversimplification.

Not every case of IBS is linked to stress. Many people with IBS aren’t particularly anxious and live relatively calm lives. For them diet, the microbiota, the after-effects of an infection or something we don’t yet understand matter more. If someone tells you that you’re “too stressed” and you don’t feel that way, you have every right to reject it.

Psychotherapy doesn’t replace the doctor and the dietitian. It is one of three paths, not a substitute for the other two. And if the picture changes — new symptoms appear, blood, weight loss — a fresh medical assessment is essential, even if the earlier IBS diagnosis was correct.

It doesn’t help everyone. Even the best-supported psychological treatments bring only a little improvement for some people. That doesn’t mean they didn’t try hard enough.

The explanation mustn’t turn into blame. “The gut–brain axis” doesn’t mean you caused your own problems. It just means there is one more path available to you along which you can change something. If at some point you feel you can’t go on, call the Samaritan helpline (Zaupni telefon Samarijan) on 116 123 in Slovenia (24 hours) or the mental distress helpline (Klic v duševni stiski) on 01 520 99 00 in Slovenia (from 7 pm to 7 am).

What to remember

• IBS is a real disorder of gut function, not imagination and not “just nerves”.
• A doctor first: other diseases need to be ruled out, and warning signs always call for an examination.
• The gut and the brain are connected in both directions — anxiety can worsen digestion and digestion can worsen anxiety.
• Fear of symptoms and avoidance can keep the problems going — and this is exactly where psychological treatment has a proven place.
• It works best when doctor, dietitian and psychological support come together.