Summary

IBS is one of the most common gut conditions in the UK, yet one of the most misunderstood. This guide looks at what is actually happening in your body when IBS develops. It explains why things can feel so unpredictable, and what a layered, root cause approach looks like in practice. It also covers the diet, herbs and nutrients with the strongest evidence.

Key takeaways

• IBS involves real, measurable changes in how your gut and your brain communicate.
• Your gut nerves, your microbiome and your gut lining can all be part of it.
• A low FODMAP diet has more trial evidence than any other diet for IBS.
• Peppermint oil capsules came first for overall relief when 51 trials of common IBS approaches were compared.
• Stress, an old gut infection and SIBO can all keep IBS going, so finding the cause is the real work.
• Support works best when it is matched to your own pattern, which is what a full case history is for.

IBS is often described as a functional gut condition, and that word tends to confuse people. Some read it as meaning nothing is really wrong. In fact it means your gut isn’t working as it should, even when a colonoscopy looks normal.

If you have IBS, you may know a particular kind of frustration. Bloating appears from nowhere, cramping comes and goes, and your bowel habits swing between constipation and diarrhoea. Perhaps you’ve been told to reduce your stress, eat more fibre or cut out certain foods. Some of that advice may have helped a little, and some may have made things worse. The advice was written for everyone with the label, yet the same label covers many different patterns. Each one is driven by a different mix of causes, and making sense of yours is where useful support begins.

Many women also notice their digestion changing through perimenopause, which I cover in the surprising gut changes in perimenopause. And, if you’re unsure whether this is IBS, my post Do I have IBS? covers the signs and types.

How your gut normally works

Your gut is far more than a tube that processes food. It holds a dense network of nerve cells, a great deal of immune tissue and trillions of microbes. Together they manage digestion, direct your immune responses and keep up a constant conversation with your brain.

The nerve network in your gut wall is called the enteric nervous system. When researchers counted the nerve cells along the human gut, they found around 168 million. That’s comparable to the number in your spinal cord. These nerves receive signals from your brain and send signals back, all along your digestive tract.

Your microbiome lives alongside those nerves. Your gut bacteria, fungi and other microbes make compounds that support your gut lining and help to regulate inflammation. They also help to shape how your body responds to stress. When all of this works well, you barely notice your gut. Digestion happens, discomfort is rare, and your bowel habits are fairly predictable.

What changes in IBS

IBS is now classed as a disorder of gut-brain interaction. That means the communication between your gut and your nervous system has become disrupted. The international Rome IV criteria describe the changes behind it. They include a more sensitive gut, altered gut movement, and changes in the gut lining and its immune activity. Changes in your gut bacteria, and in how your brain processes signals from your gut, belong on that list too.

A gut that feels too much

One of the most consistent findings in IBS is visceral hypersensitivity. It means your gut is more sensitive than it should be. Ordinary events, such as food moving through or wind passing, register as uncomfortable or even painful. That’s because the nerve pathways carrying sensation from your gut to your brain have become amplified. It reflects real changes in how signals are processed, both in your gut wall and in your brain. That’s why IBS can feel out of proportion to what is actually happening. A little wind that someone else wouldn’t notice can feel acutely painful. Pain signalling of this kind also links IBS with fibromyalgia, as I explain in the link between fibromyalgia and IBS.

Stress and your nervous system

Your nervous system has a strong influence over how your gut works. Under sustained stress, the balance moves towards your sympathetic nervous system, the alert state built for short bursts of threat. In that state your digestion slows and your immune system becomes more reactive. When the alert state lasts for months, those changes can become habitual, and your gut bears the brunt. It’s a physiological change in how your nervous system regulates your gut. Many people with IBS have a history of prolonged stress, difficult early experiences or a severe gut infection.

Changes in your gut lining

IBS also involves changes at your gut lining. The thin layer of cells lining your gut can become more permeable than it should be. Small particles from food and bacteria can then cross into your gut wall and set off your immune system. This doesn’t cause the visible inflammation of Crohn’s disease or ulcerative colitis. But, it creates a background irritation that adds to pain, urgency and altered bowel movements.

IBS after a stomach bug

Post-infectious IBS is a well recognised pattern. It develops after a bad gut infection, even once the infection itself has cleared. Researchers pooled 45 studies of more than 21,000 people. About one in ten had IBS a year after a gut infection. Women were more than twice as likely to develop it, and antibiotics during the illness also raised the risk. Your gut lining and immune tissue can take far longer to recover than the infection did.

Your microbiome and IBS

Your gut microbiome is central to IBS, in ways that are still being worked out. A healthy microbiome is diverse, with many species living in fairly stable proportions. That diversity helps to regulate inflammation, produce protective compounds and keep your gut lining intact. In IBS the balance is often disturbed, which is called dysbiosis. What it looks like varies from person to person. Some people have fewer beneficial bacteria, such as Bifidobacterium. Others have more of the microbes linked with gas production or irritation of the gut lining.

Serotonin and your gut

Your microbiome also plays a part in serotonin signalling. More than 90 per cent of your body’s serotonin is made in your gut, by specialised cells in its lining. In the same research, carried out in mice, certain gut bacteria increased how much serotonin those cells produced. That in turn changed how fast the gut moved. Serotonin helps to regulate gut movement, and it also influences your mood, sleep and how you feel pain. Low mood, poor sleep and anxiety can occur alongside IBS because they share some of the same signalling.

You might also like my post: Why Does My Stomach Gurgle Even When I’m Not Hungry

SIBO: when bacteria are in the wrong place

Small intestinal bacterial overgrowth, or SIBO, has changed how many practitioners understand IBS. It means too many bacteria in the small bowel. Your small intestine is mainly a place for absorbing food, and it isn’t meant to hold large numbers of bacteria. When bacteria move up from the large intestine, or multiply where they are, they ferment carbohydrates too early. That early fermentation produces gas, bloating and changes in your bowel habits, which can look exactly like IBS. SIBO is found in a substantial share of people with IBS, though estimates vary with the testing method used.

Hydrogen, methane and hydrogen sulphide

There are different types, and they tend to produce different patterns. Where hydrogen is the main gas, loose stools and urgency are more common. Where methane is the main gas, the organisms responsible are archaea, a separate group of microbes from bacteria. This type is now called intestinal methanogen overgrowth, or IMO. Methane slows your gut. So, IMO tends to bring constipation, persistent distension and a gut that seems to take days to clear. A third type, linked with hydrogen sulphide, is less studied. It’s associated with gut pain and wind that smells of sulphur. Knowing which pattern is present shapes the support, because what helps one type can do little for another.

You might also like my post: SIBO: It’s important to find the possible causes

Understanding what is driving your pattern

Because IBS involves several systems, it helps to know which ones are most active in you. A thorough assessment draws on a detailed case history, the pattern of what you’re experiencing and, where it’s useful, testing.

Breath testing

A breath test can identify SIBO or IMO. You drink a measured amount of a sugar that bacteria ferment, then breathe into tubes at regular intervals. The North American consensus on breath testing sets the thresholds. A rise in hydrogen of 20 parts per million within 90 minutes counts as SIBO. A methane level of 10 parts per million or more counts as positive for methane.

Stool testing

A comprehensive stool test gives a different layer of information. Modern stool tests use DNA methods to identify harmful bacteria, parasites and levels of beneficial bacteria. They also include markers of how well you digest food and of the health of your gut lining. Calprotectin, measured in a stool sample, shows inflammation in the bowel wall. It helps to tell IBS apart from inflammatory bowel disease, although no single marker identifies IBS on its own.

Food sensitivity testing

Some practitioners use IgG food sensitivity testing to identify foods you react to. It remains a contested area, because IgG antibodies show exposure to a food as well as a reaction to it. The results therefore need careful interpretation. In practice, an elimination diet guided by IgG results sometimes helps when other changes in diet haven’t. I’ve written more about food reactions in Why am I reacting to everything I eat?

What to eat with IBS

Diet is usually the first thing people try when they have IBS. The challenge is that no single way of eating suits every pattern.

The low FODMAP approach

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These carbohydrates are poorly absorbed in your small intestine and easily fermented by bacteria. For someone with IBS, cutting them back for a while can help a great deal. That’s particularly true where overgrowth or dysbiosis is involved. When researchers compared 13 trials of diets for IBS in 944 people, the low FODMAP diet ranked first. It came top for overall relief, abdominal pain and bloating.

The diet starts with a short, structured phase. Foods are then brought back one group at a time to find your own triggers. Long term restriction of foods such as garlic, onions and pulses reduces the food available to your beneficial bacteria. Over time that can reduce the diversity of your microbiome, so the reintroduction phase isn’t optional. I cover how it’s done in the three phases of the low FODMAP diet and my low FODMAP food list.

Why fibre type matters

People with IBS are often told to eat more fibre, and on its own that advice is incomplete. Soluble fibre dissolves in water to form a gel. It softens your stools in constipation, adds bulk in diarrhoea and moves through your gut without irritating it. You’ll find it in oats, psyllium, flaxseed, peeled fruit and root vegetables. Kiwifruit deserves a mention of its own. Two green kiwifruit a day eased constipation and discomfort in a trial of 184 people across three countries. I’ve written about the health benefits of kiwifruit.

Insoluble fibre, found in wheat bran, vegetable skins and whole grains, doesn’t dissolve. It suits some people, but in a sensitive gut it can irritate, particularly during a flare. NICE guidance on IBS advises soluble fibre such as oats, and discourages bran.

You might also like my post: Okra for Gut Health: Benefits, Uses & Recipes

Meal rhythm and daily habits

When you eat matters as much as what you eat. Regular meals help to keep your migrating motor complex working. This is the cleansing wave that sweeps through your small intestine between meals. Skipping meals or eating at erratic times can disrupt it, and that can let bacteria build up. Drinking enough fluid supports your gut movement. Caffeinated drinks stimulate gut contractions and can make urgency worse. So, cutting back on tea and coffee can help when urgency or loose stools are the main problem.

You might also like my post: 10 Mediterranean Foods to Soothe Your Digestive System

Herbal medicine for IBS

Herbal medicine has a long history in digestive care, much of it for exactly what IBS brings. Peppermint, chamomile, caraway, fennel and slippery elm have been used for wind, cramping and an irritated gut for centuries. Modern research now shows that several of these herbs act on the mechanisms that drive IBS.

Peppermint

Peppermint has been used for digestion for as long as there are herbal records. Its oil is also the most studied herb in IBS. European guidance recognises peppermint oil for minor spasms, wind and abdominal pain, especially in IBS. Menthol, its main active compound, blocks calcium channels in the smooth muscle of your gut wall. That relaxes the involuntary contractions that cause cramping and spasm. Peppermint oil also acts on pain receptors in your gut wall, so it eases pain as well as spasm.

Across ten trials in 1,030 people, peppermint oil improved IBS overall, and abdominal pain, more often than placebo. When researchers ranked the common approaches to IBS across 51 trials, peppermint oil capsules came first for overall relief. The capsules are enteric coated, so the oil is released in your small intestine instead of your stomach. Peppermint oil can make reflux worse, so heartburn is the one reason to leave it out. Peppermint tea is gentler, and it’s low in FODMAPs.

Chamomile, lemon balm and the soothing herbs

Chamomile is one of the gentlest herbs for an unsettled gut. It has been used for bloating and cramping for centuries. The European monograph for chamomile gives it for minor gut complaints such as bloating and minor spasms. Lemon balm has a matching entry for bloating and wind, and it calms your nervous system at the same time. That suits IBS well, since your gut and your nervous system are so closely linked.

Caraway and fennel are the classic carminatives, the herbs that help trapped wind to move on. Caraway and fennel both have European monographs for bloating and wind. Slippery elm is the herbalist’s classic demulcent, a bark whose mucilage coats and soothes an irritated gut lining. In a small open study, ten people with IBS and constipation took a slippery elm formula. It also contained oat bran, liquorice and lactulose. Their bowel habit, bloating and pain all improved. Chamomile and fennel teas are both high in FODMAPs. On a low FODMAP diet, they’re best tested during reintroduction.

You might also like my post: Chamomile: best for a bloated belly

Iberogast

Iberogast is a herbal blend that has been used in European clinics for decades. Its newer formula, known as STW 5-II, combines bitter candytuft, peppermint, chamomile, liquorice, caraway and lemon balm. Each herb contributes something different, and together they act on several parts of gut function at once. A trial of 208 people with IBS tested the original blend and the newer formula against placebo. Both reduced abdominal pain and overall IBS scores. The trial also tested bitter candytuft on its own, and it was the full blends that made the difference.

Herbal antimicrobials and berberine

Where SIBO is part of the pattern, oregano oil, neem and berberine are among the antimicrobials most often used. Berberine is a compound extracted from plants such as barberry and goldenseal, then concentrated and sold on its own. A study of 104 people with SIBO compared two commercial herbal blends with an antibiotic. After four weeks, the herbs cleared the breath test in 46 per cent. Rifaximin, the standard antibiotic for SIBO, cleared it in 34 per cent. Of 14 people whose SIBO hadn’t cleared on rifaximin, eight then cleared on the herbal blends.

Concentrated plant oils and isolated compounds are powerful, and berberine acts on the liver enzymes that clear many medicines. So, if you take prescribed medication, ask a medical herbalist before starting it.

Triphala

Triphala is an Ayurvedic formula made from three fruits: amalaki, bibhitaki and haritaki. It has been used for centuries for constipation and sluggish digestion, and it’s a cornerstone of Ayurvedic gut care. Research is starting to explain how it works. Alongside its gentle laxative action, laboratory work suggests its polyphenols encourage Bifidobacteria and Lactobacillus in the gut. In herbal practice it’s used for constipation predominant IBS, as part of a wider plan.

Nutritional support for your gut lining

L-glutamine

L-glutamine is an amino acid and the main fuel for the cells lining your intestine. When your gut lining is damaged or too permeable, those cells need that fuel to repair. In a trial of 106 people, everyone had IBS with diarrhoea and a leaky gut lining after a gut infection. Four in five improved on glutamine over eight weeks, against about one in twenty on placebo. Their gut permeability also returned to normal, which it didn’t on placebo. That makes glutamine especially relevant in post-infectious IBS, where the lining may not have fully recovered.

Zinc carnosine

Zinc carnosine combines zinc with carnosine, a compound made from two amino acids. In a small trial in ten healthy volunteers, it prevented the rise in gut permeability caused by the painkiller indomethacin. In the same study, laboratory and animal work showed it helped damaged gut cells to repair. It’s often used alongside L-glutamine to support the gut lining.

Digestive enzymes

When food isn’t fully broken down higher up, the undigested part travels further and is fermented by bacteria. That fermentation adds to wind and bloating. Digestive enzymes containing amylase, protease, lipase and lactase can help to make digestion more complete. They work alongside other support, and they can reduce how much food is left over to ferment. Low stomach acid can be part of this too, which I cover in my guide to low stomach acid.

Targeted probiotics

Probiotics don’t all do the same thing, because each strain has its own effects. In IBS, the evidence belongs to particular strains, so the strain on the label matters.

Bifidobacterium longum subsp. infantis 35624 was first studied under the name B. infantis 35624. In a trial of 362 women with IBS, one dose of it eased abdominal pain and bloating more than placebo. Two other doses did no better than placebo, so the dose tested matters too. An earlier trial found it brought the balance of inflammatory and calming immune signals back to normal.

Lactobacillus plantarum 299v has since been renamed Lactiplantibacillus plantarum 299v. It eased pain and bloating in a trial of 214 people with IBS over four weeks. Lactobacillus acidophilus NCFM has been studied for gut pain. In mice and rats, it increased opioid and cannabinoid receptors in the gut lining. That reduced the animals’ gut pain in a similar way to morphine.

You might also like my post: Reinoculate with Probiotics, 4R Gut Health

Magnesium

Magnesium relaxes smooth muscle and supports your nervous system, and its form decides what it does in your gut. Magnesium citrate is poorly absorbed in your small intestine, so it travels on to your colon and draws in water. That makes it useful for constipation predominant IBS and for the slow transit of IMO. Magnesium glycinate is magnesium bound to glycine, an amino acid, and it’s absorbed more readily without a laxative effect. It suits people who want magnesium for relaxation and sleep without a change in their bowel habit.

You might also like my post: Haemorrhoids During Perimenopause

Calming your nervous system

No guide to IBS would be complete without your nervous system. Your gut and brain are in constant communication, and the vagus nerve is one of the main routes. It runs from your brainstem down through your chest into your abdomen. Along the way it connects with your heart, your lungs and the whole length of your digestive tract.

Vagal tone

Vagal tone describes how strongly your rest and digest system is working. Good vagal tone lets your body move smoothly from an alert state back to rest. It also keeps the migrating motor complex working between meals. That helps to stop bacteria building up in your small intestine. Low vagal tone is common with prolonged stress, difficult early experiences or ongoing health problems. It’s linked with slower gut transit, a more sensitive gut and stronger reactions to daily stress. Vagal tone can improve with regular practice.

Simple ways to support your vagus nerve

• Slow breathing. Breathing slowly from your diaphragm, with a longer breath out than in, engages your vagus nerve. Five minutes before a meal is a good start, and it doesn’t need to be formal meditation.
• Cold water. Splashing cold water on your face for about 30 seconds sets off the dive reflex, which increases vagal activity.
• Humming and gargling. Humming, chanting and gargling vigorously all vibrate the throat muscles your vagus nerve supplies. Practised regularly, they may help to improve your vagal tone over time.

Gut-directed hypnotherapy

Gut-directed hypnotherapy works on how your brain interprets signals from your gut. Through guided relaxation and visualisation, it reduces the constant watchfulness that amplifies uncomfortable sensations in IBS. A trial of 74 people compared hypnotherapy with the low FODMAP diet. Each helped about seven in ten people within six weeks. The benefit held six months later for most people in both groups, and hypnotherapy also eased anxiety. It’s available from trained practitioners and through structured digital programmes, so it’s easier to find than it once was.

Finding what’s behind your IBS

With so many possible approaches, it’s easy to feel overwhelmed. IBS usually has a cause underneath it. That might be an old infection, SIBO, a long stretch of stress or changes in your gut lining. Unless that cause is found and dealt with, the problem tends to come back, whatever helps in the meantime. The order of support matters too. Adding lots of prebiotic fibre to a gut with marked overgrowth can make bloating worse. So, where SIBO is likely, it’s usually tested for and addressed before the microbiome is rebuilt. Finding the cause takes a full case history and training, which is what herbalists are taught to do. That case history also picks up the few red flag signs that need investigating first. Bleeding, unexplained weight loss, IBS type changes that began after 50, or pain that wakes you at night are the main ones. They are uncommon. But if one came up at your consultation, I would refer you to your GP before we went further.

While you’re waiting to be seen, a few simple things can help. Eat regular meals, and choose soluble fibre such as oats over bran. Peppermint tea after meals and a few minutes of slow breathing before them are both easy to try. Keeping a simple diary of what you eat, and how your gut responds, can also show a pattern.

IBS can also change over time. What set off your gut at one stage of life may not be the same years later. If something that used to help has stopped working, the pattern deserves a fresh look.

Frequently asked questions

What causes IBS?

There can be many causes, and they often work together. A more sensitive gut, stress, an old gut infection, SIBO and changes in your microbiome are all recognised drivers.

Can herbal medicine help IBS?

Peppermint oil has the strongest trial evidence, and in ten trials it improved IBS more often than placebo. Chamomile, lemon balm, caraway, fennel and slippery elm have a long traditional use for bloating, wind and cramping.

How long should I follow a low FODMAP diet?

The first, stricter phase lasts a few weeks. Foods are then brought back one group at a time, and that reintroduction phase protects your microbiome.

Does stress cause IBS?

Stress is one of several drivers. Prolonged stress slows digestion, makes your immune system more reactive and can make your gut more sensitive.

Which probiotic is best for IBS?

The evidence belongs to specific strains. Bifidobacterium longum subsp. infantis 35624 and Lactobacillus plantarum 299v each eased pain and bloating in trials. Check the strain on the label.

Does IBS need testing?

Not always. A detailed case history often shows the pattern. Where it’s useful, breath testing for SIBO and a comprehensive stool test add another layer.

Where this leaves you

IBS is complex, and it isn’t yet fully understood. There is now a much clearer view of the real changes involved. A more sensitive gut, disrupted signalling between gut and brain, and a changed microbiome are all well documented. So are low-grade immune activity and a gut lining that has become too permeable. These changes are real, and they respond to real support. The challenge is matching that support to your own pattern. Someone with IMO and constipation needs a different approach from someone with diarrhoea after a gut infection. With the right support, IBS can become manageable for many people. That can mean getting on with your life again.

If you’d like to talk things through, you’re welcome to book a free hello call. We can look at what’s been happening with your gut, and whether working together might help.