Stress and gut health. How cortisol affects your gut and what helps

In a 2014 study, healthy volunteers had to give a public speech. Afterwards, their small intestine let more through its lining than usual. The change only showed up in the people whose cortisol, the main stress hormone, went up. That small study shows how closely stress and gut health are tied together.

I lived with IBS with diarrhoea myself, so I know how much the mind and the gut affect each other. In this guide I explain what stress and cortisol do inside your gut and how your gut bacteria join in. I also cover which calming steps have real evidence.

What happens in your gut when you are stressed?

When you are stressed, your brain sends signals that change how your gut moves, feels and protects itself. Your body runs a stress system called the HPA axis. HPA stands for hypothalamus, pituitary and adrenal.

1. Your brain’s hypothalamus releases a hormone called CRH.
2. CRH tells your pituitary gland to release a second hormone called ACTH.
3. ACTH tells your adrenal glands, which sit on your kidneys, to release cortisol.

CRH does not only act in the brain. It also acts on the gut directly. Your brain and gut also talk through the vagus nerve, your immune system and chemicals made by gut bacteria. A major 2019 review described this as the microbiota-gut-brain axis. It said stress can affect this axis at every stage of life.

My guide to the gut-brain axis explains the basics in more detail. Here I focus on stress and cortisol.

Can stress cause diarrhoea and belly cramps?

Yes, stress hormones can speed up your bowel and make cramps more likely. In a 1998 study, researchers gave CRH by drip to 10 people with IBS and 10 people without it. CRH made the lower colon move more in both groups.

The colon moved even more in people with IBS. Their belly symptoms also lasted longer, and their ACTH levels rose higher. The authors said the brain-gut link in IBS may overreact to CRH. This is a small and older study, but it helps explain why many people rush to the toilet before an exam or a big meeting.

Does stress make your gut leaky?

Short-term stress can make your gut lining let more through for a while. In the 2014 study I opened with, 23 healthy volunteers were tested under different conditions. Public speaking raised gut permeability and cortisol. A threat of mild electric shocks did neither.

The researchers then gave CRH alone, and it raised permeability too. A drug that calms mast cells, a type of immune cell in the gut wall, blocked the effect of both stress and CRH. So stress seems to open the gut barrier partly through these immune cells.

Long physical stress shows a similar pattern. A 2017 study followed 73 soldiers on a 4-day cross-country ski march. Their gut permeability rose by 62% on average. More than half of the bacteria groups the team identified changed in amount, and inflammation markers went up.

These studies show short-term changes in healthy people. They do not prove that stress causes long-term gut damage. But I strongly believe this is one reason stress so often shows up in the gut first.

Does stress change your gut bacteria?

Yes, stress can change your gut bacteria, and your gut bacteria can change how you handle stress. In the soldier study, the gut bacteria shifted within just 4 days of hard training.

The other direction is clearest in animals so far. A 2004 study compared mice raised with no gut bacteria to normal mice. The germ-free mice released far more stress hormones when they were held still. Giving them one helpful Bifidobacterium strain reversed this, but only when it was given early in life.

We cannot copy mouse results straight onto people. Still, these findings support what I see in practice. When I work with a client’s gut, I always look at their stress and sleep too.

Can stress cause IBS?

Stress and anxiety can raise the chance of IBS, and IBS can raise anxiety too. A 2012 Australian study followed 1,002 adults for 12 years. Among people with no gut disorder at the start, higher anxiety predicted new gut disorders later.

The reverse was also true. People who had a gut disorder but no raised anxiety at the start had more anxiety and depression 12 years later. The authors concluded that the brain and gut affect each other in both directions.

This matters because it means IBS is not “just stress”. It also means calming your nervous system is a real gut treatment. My guide to IBS and anxiety covers this loop in more depth.

Is cortisol always bad for you?

No, cortisol is not a villain. You need it to wake up, keep your blood sugar steady and handle danger. It normally peaks in the morning and falls through the day. Problems come when stress keeps going with no recovery time.

You may see claims about “adrenal fatigue” and products to fix it. A 2016 review screened 3,470 papers and looked closely at 58 studies of cortisol and tiredness. It found no evidence that adrenal fatigue is a real medical condition.

Be careful with supplements sold to “lower cortisol” or “heal your adrenals”. If you feel exhausted all the time, see your doctor. Tiredness has many causes, and some need real tests. If stress shows up around your middle, my article on stress belly explains what helps.

What helps stress and gut health the most?

The steps with the best evidence calm your nervous system and feed your gut bacteria at the same time. Here is what I suggest.

Try slow breathing every day

A 2023 review pooled 12 trials with 785 adults. Breathwork lowered stress more than control groups did. The effect was small to medium, and the authors urged caution because many trials were at some risk of bias. Try my guided Breathe With Me exercise for 2 minutes before meals.

Feed your gut bacteria

In a 2023 Irish trial, 45 adults ate a diet rich in fibre and fermented foods or followed a control diet for 4 weeks. Perceived stress fell by 32% on the gut diet and 17% on the control diet. The gap between groups was not statistically clear, but people who followed the diet most closely improved the most.

Fibre-rich foods include oats, beans, lentils, fruit, vegetables, nuts and seeds. Fermented foods include yogurt, kefir and sauerkraut. If you have IBS, add these slowly and pick low FODMAP options first. My guides to fermented foods and 30 plants a week show how.

Move your body most days

Walking and yoga are gentle ways to ease stress and keep your bowel moving. My guide to exercise for IBS explains which types help most.

Ask about gut-directed therapy

For IBS, psychological therapies have strong evidence. A 2020 review of 41 trials with 4,072 people found that cognitive behavioural therapy (CBT) and gut-directed hypnotherapy helped the most. The trials had a high risk of bias, so the true effect may be smaller. Read my guide to hypnotherapy for IBS to see what a course involves.

Keep regular meals and protect your sleep

Skipping meals and sleeping badly are both stress on your body. In my clinic I always ask about sleep hours and sleep quality, alongside gut symptoms. Eat at similar times each day and give yourself a calm wind-down before bed.

Be realistic about probiotics for stress

Some probiotic strains show early promise for stress. In a 2016 study of 22 healthy volunteers, one Bifidobacterium longum strain reduced the rise in cortisol and anxiety during a cold-water stress test. A 2025 trial in 79 students found that a probiotic fermented milk kept gut bacteria more stable before exams.

These are small studies, and the 2025 result came from extra analysis done after the trial. I would not buy a probiotic just for stress yet. My guide to probiotics for IBS covers strains with stronger gut evidence.

If you want help building these habits, my free 30-Day Calm Gut Challenge gives you one small calming step each day.

When should you see a doctor?

Stress can cause real gut symptoms, but it should not be the first explanation for warning signs. See a doctor if you have blood in your stool, diarrhoea that wakes you at night or ongoing vomiting. Losing 3 kg (about 7 lb) or more without trying also needs a check.

Please also get help if stress or anxiety is affecting your daily life. Talking to a doctor or therapist is a strong step, not a weak one. It is also worth learning which beliefs about your gut are not true, which I cover in my guide to gut health myths.

Frequently asked questions

Can stress cause stomach problems?

Yes. Stress hormones such as CRH can speed up your colon and make your gut more sensitive. Short bursts of stress can also make your gut lining let more through for a while. This is why stress can bring on diarrhoea, cramps, bloating or nausea, especially if you have IBS.

How can I calm my gut from stress fast?

Slow breathing is the quickest tool with trial evidence. Breathe in gently through your nose and breathe out for longer than you breathe in, for 2 to 5 minutes. A short walk, a warm drink and sitting down to eat slowly can also help your gut settle.

Does high cortisol cause bloating?

Cortisol is part of the stress response, and stress can make bloating feel worse, especially with IBS. But bloating has many causes, such as constipation, certain foods and swallowed air. There is no reliable home test that links your cortisol to your bloating, so look at your whole routine.

Can probiotics lower cortisol?

One small study found that a Bifidobacterium longum strain lowered the cortisol rise during a stress test in 22 healthy people. That is a promising start, not proof. A diet rich in fibre and fermented foods is a safer first step for most people, and it feeds many helpful bacteria at once.

How do I know if my gut problems are from stress?

A food and mood diary for 2 weeks is a good start. Note your stress level, meals, sleep and gut symptoms each day. If symptoms rise on stressful days, stress is likely part of the picture. Always see a doctor first about new or worrying symptoms.

What I want you to remember

Stress and gut health are linked in both directions. Stress hormones can speed up your bowel, open your gut lining for a while and shift your gut bacteria. Your gut bacteria may also shape how strongly you react to stress.

The good news is that the fixes are simple and work on both sides at once. Breathe slowly, eat plenty of plants and fermented foods, move often, sleep well and ask about gut-directed therapy if you have IBS. Calming your mind is a real gut treatment.