IBS

What is happening

Several mechanisms, in different mixtures in different people:

• Visceral hypersensitivity — the gut's nerves signal pain at levels of stretch that would go unnoticed in someone else. This is measurable, not imagined
• Altered gut motility — muscle contractions too fast, too slow or uncoordinated
• Gut–brain axis dysfunction — the nerve traffic between gut and brain runs both ways, which is why stress genuinely alters bowel function and why drugs acting on nerve signalling help
• Changes in the gut microbiome, particularly after infection or antibiotics
• Low-grade immune activation in the bowel wall in some people

What sets it off

• Gastroenteritis — post-infectious IBS. A recognised and common trigger; many people can name the exact illness or holiday it began with. It usually improves over months to a couple of years
• Antibiotic courses
• Significant stress or a difficult life period
• Adverse experiences in childhood, which are associated with IBS in adulthood — not a moral point, a physiological one about how pain pathways develop
• Family history

Who gets it

Twice as common in women. Usually starts before 50 — which is exactly why onset after 50 should not be assumed to be IBS.

The conditions that masquerade as IBS

This list is the reason the initial tests matter:

• Coeliac disease — presents identically and is missed for years. Test before cutting out gluten, or the test will not work
• Inflammatory bowel disease — Crohn's or ulcerative colitis. Faecal calprotectin separates them from IBS cheaply and quickly
• Bile acid malabsorption — causes watery diarrhoea often labelled IBS-D for years. It is diagnosed with a SeHCAT scan and responds dramatically to a bile acid binder. Genuinely under-diagnosed, and worth asking about if your "IBS" is mostly urgent morning diarrhoea
• Ovarian cancer — bloating, discomfort and altered bowel habit. Never assume IBS in a woman over 50 with new persistent bloating
• Bowel cancer — the reason the red flags exist
• Thyroid disease — an overactive or underactive thyroid changes bowel habit
• Lactose intolerance, and pancreatic insufficiency
• Endometriosis — frequently mislabelled as IBS, particularly where pain is cyclical and sex is painful. See endometriosis
• Medication — metformin, some antidepressants, iron, magnesium and others

IBS is diagnosed on the pattern of symptoms plus a limited set of tests, and that combination works well in a remote consultation.

The pattern that makes it a positive diagnosis

Abdominal pain or discomfort related to opening your bowels, with a change in stool frequency or form, present over at least several months. Supported by bloating, urgency, straining, mucus, and symptoms worse after eating and better after passing a stool.

The tests that should be done in everyone

• Full blood count — anaemia points away from IBS
• CRP or ESR
• Coeliac serology — tTG-IgA with total IgA, while still eating gluten
• Faecal calprotectin — a stool test that reflects bowel inflammation and reliably separates IBS from inflammatory bowel disease. The test most often missed, and the one that prevents years of a wrong label
• Thyroid function, and ferritin

Additional tests where the picture warrants it

• CA125, in any woman with persistent bloating — particularly over 50, and alongside a pelvic ultrasound where indicated. Non-negotiable, given how often ovarian cancer arrives dressed as IBS
• FIT testing where there is any question of bowel cancer
• SeHCAT for suspected bile acid malabsorption, where diarrhoea dominates
• Breath testing for lactose intolerance or bacterial overgrowth, in selected cases

Tests that are not needed — and one to avoid entirely

• Colonoscopy is not required for typical IBS in someone under 50 with normal tests and no red flags
• Ultrasound and CT rarely add anything in typical IBS
• IgG "food intolerance" blood tests have no diagnostic validity. They generate long lists of foods to avoid, cause unnecessary dietary restriction, and are not accepted by any allergy or gastroenterology body. We will not act on them

When to refer

Any red flag; symptoms not responding to proper treatment; and diagnostic uncertainty. Urgent referral for bleeding, weight loss, a mass, iron deficiency anaemia, or new symptoms over 50.

Worth reading alongside this: our article on the questions to ask before accepting an IBS diagnosis.

The basics, which do more than they sound like they would

• Eat regularly and do not skip meals. Long gaps followed by a large meal provoke symptoms reliably
• Eat slowly and sitting down; eating fast swallows air and worsens bloating
• Limit caffeine — a strong stimulant of bowel contraction
• Reduce alcohol and fizzy drinks
• Avoid sweeteners ending in "-ol" — sorbitol, mannitol, xylitol — in sugar-free gum, mints and drinks. A remarkably common and easily missed cause of bloating and diarrhoea
• Drink enough water, especially if increasing fibre

Fibre, correctly

Soluble, not insoluble. Oats, linseed, ispaghula, pulses, carrots and potatoes — not wheat bran. Increase gradually over weeks, and accept a temporary increase in wind while your gut adjusts.

Movement and stress

• Regular exercise has genuine trial evidence in IBS — walking, swimming, cycling. Not simply general advice
• Yoga has specific evidence too
• Stress management is treatment here, not a platitude. The gut–brain connection is a physical nerve pathway, and reducing the load on it changes symptoms
• Sleep matters — poor sleep measurably worsens gut sensitivity

Keeping a diary

Two to four weeks of food, symptoms, stress and, for women, cycle day. It identifies patterns you will not otherwise see — particularly the cyclical pattern many women have, and the delayed reaction to foods eaten the day before.

Things that make it worse

• Wheat bran — the classic wrong advice
• Lactulose — ferments and worsens bloating
• Long-term restrictive diets without professional guidance. Cutting out more and more foods narrows nutrition and the microbiome, and it is a common trap
• Repeated antibiotic courses
• Codeine-based painkillers, which cause constipation and worsen pain over time
• Chasing a diagnosis through IgG intolerance tests, which produce long avoidance lists with nothing behind them

Two things worth holding on to

IBS does not damage your bowel, does not become inflammatory bowel disease, and does not cause cancer. That reassurance is not a consolation prize — fear of something serious measurably worsens symptoms, so genuinely absorbing it is part of the treatment.

But if something changes, get it reassessed. Having IBS does not protect you from developing something else, and new bleeding, weight loss or symptoms waking you at night should never be attributed to a label you were given years ago.

Is IBS a real diagnosis, or just what they say when they can't find anything?

It is a real diagnosis with measurable mechanisms — the gut's nerves signal pain at normal levels of stretch, and its muscle coordination is altered. It should be made positively, on a recognisable pattern plus specific tests, not assigned by default. If nobody explained why it is IBS rather than something else, that is a fair question to put back to them.

Which tests should I have had?

At minimum: full blood count, inflammatory markers, coeliac serology (tTG-IgA with total IgA, while still eating gluten), and faecal calprotectin — a stool test that separates IBS from inflammatory bowel disease. Calprotectin is the one most often missed. In women with persistent bloating, add CA125.

Should I try a gluten-free diet?

Get tested for coeliac disease first. The blood test only works if you have been eating gluten regularly for at least six weeks, so cutting it out beforehand makes the diagnosis impossible to confirm — and coeliac disease is missed for years exactly this way. Once that is excluded, a trial is reasonable.

Does the low FODMAP diet work?

Yes, for around three in four people — it has the best dietary evidence in IBS. But it is a three-phase process, not a permanent diet: restrict for four to six weeks, then systematically reintroduce, then settle on your own list. Staying in the restriction phase for months narrows your nutrition and your gut bacteria. It genuinely warrants a dietitian.

Should I be eating more fibre?

The right kind. Soluble fibre — ispaghula, oats, linseed — helps. Insoluble fibre, especially wheat bran, makes IBS worse, and "eat more bran" has done real damage as advice. Build up slowly and expect a couple of weeks of extra wind before it settles.

My main problem is urgent diarrhoea, especially in the morning.

Worth asking specifically about bile acid malabsorption. It causes exactly that pattern, is regularly labelled IBS-D for years, is diagnosed with a SeHCAT scan, and responds dramatically to a bile acid binder. One of the most satisfying things to find, and one of the most under-diagnosed.

Why has amitriptyline been suggested when I'm not depressed?

Because at the low doses used here it is not working as an antidepressant. It acts on the nerve signalling between gut and brain, reducing pain sensitivity and slowing the bowel — which is why it is particularly useful in IBS-D. The dose is a fraction of the antidepressant range, and the reason for it should always be explained.

Does hypnotherapy actually work?

Yes — gut-directed hypnotherapy has strong trial evidence in IBS, with benefits lasting years, and it is one of the most under-offered treatments in this whole area. It is not general relaxation; it targets the gut–brain pathway specifically. On the evidence it deserves to be offered early rather than as a last resort.

Could this be something more serious?

IBS does not damage the bowel, does not turn into inflammatory bowel disease and does not cause cancer. But certain features mean it should not be assumed: bleeding, weight loss, anaemia, symptoms waking you at night, a family history of bowel or ovarian cancer, or new symptoms starting over 50. And persistent bloating in a woman always deserves ovarian cancer excluded rather than an IBS label.