Irritable bowel syndrome (IBS): symptoms, diagnosis, diet and treatment

IBS is a disorder of how the gut behaves rather than a disease that damages it. The tests used in assessment are mainly there to rule out other conditions. The NHS says the exact cause is unknown, with links to food moving through the gut too quickly or too slowly, an oversensitive gut, a past episode of gastroenteritis, stress and a family history of IBS.

It tends to come in waves. The NHS explains symptoms come and go over time and can last for days, weeks or months at a time, and that it can be very frustrating to live with and can have a big impact on daily life. NICE guideline CG61 asks clinicians to recognise the chronic nature of IBS and the limits of current knowledge about it.

The NHS gives four main symptoms: pain or cramps that are usually worse after eating and better after doing a poo, bloating that makes the tummy feel full and swollen, diarrhoea with watery poo and sometimes sudden urgency, and constipation with straining and a feeling of incomplete emptying. There can be days of relief and days of flare-up.

Flare-ups sometimes have no clear reason, and sometimes follow alcohol, caffeine, spicy or fatty foods, stress and anxiety or regular antibiotic use, according to the NHS. Other possible features include wind, mucus in the poo, tiredness, nausea, backache, bladder symptoms such as needing to pee often or urgently, occasional loss of bowel control and pelvic pain.

• Abdominal pain or cramping that eases after opening the bowels.

• A swollen, uncomfortably full tummy.

• Watery stools with urgency, constipation with straining, or alternating patterns.

• Wind, mucus, tiredness, nausea, backache and bladder symptoms.

A GP asks about the symptoms, whether they come and go, how often they occur, whether certain foods are linked and how long they have lasted, and may feel the tummy for lumps or swelling. The NHS says a symptom diary can help.

NICE guideline CG61 says clinicians should consider IBS if a person has had abdominal pain or discomfort, bloating or a change in bowel habit for at least 6 months. A diagnosis should only be considered if the pain is relieved by opening the bowels or linked to altered stool frequency or form, together with at least two of four features: altered stool passage such as straining, urgency or incomplete emptying; bloating or distension; symptoms made worse by eating; and passing mucus.

The tests are about exclusion. The NHS says a GP may arrange a blood test to check for problems such as coeliac disease and stool tests for infection and inflammatory bowel disease. NICE lists a full blood count, ESR or plasma viscosity, C-reactive protein and coeliac antibody testing, and says that ultrasound, colonoscopy, sigmoidoscopy, thyroid function tests and breath tests are not needed to confirm IBS in people who meet the criteria.

Bleeding, large unexplained weight loss and a lump are not among the symptoms the NHS lists for IBS. It says to ask for an urgent GP appointment or contact NHS 111 if you have lost a lot of weight for no reason, are bleeding from the bottom or have bloody diarrhoea, find a hard lump or swelling in your tummy, or have shortness of breath, noticeable heartbeats and paler skin than usual. These could be signs of something more serious.

NICE says everyone with possible IBS symptoms should be examined for red flag features and referred to secondary care if signs and symptoms of cancer are present or inflammatory markers suggest inflammatory bowel disease. It also notes that IBS pain can occur anywhere in the abdomen and varies, which helps distinguish it from cancer-related pain that typically has a fixed site.

The NHS says there is no single diet or medicine that works for everyone. General advice is to eat a healthy balanced diet, keep a food and symptom diary, drink 8 to 10 drinks (about 1.5 litres) of non-caffeinated fluid a day, relax, exercise and consider probiotics for a month. Things to avoid are skipping meals, eating too quickly, fatty, spicy or processed foods, more than 3 portions of fruit or 3 caffeinated drinks daily, and lots of alcohol or fizzy drinks.

NICE adds that insoluble fibre such as bran should be discouraged, and soluble fibre such as oats preferred where more fibre is advised. People who try probiotics should use them for at least 4 weeks while monitoring effect, and aloe vera is discouraged. If symptoms persist, NICE says further dietary management such as single food exclusion or a low FODMAP diet should be given only by a healthcare professional with dietary expertise. The NHS says a GP may refer to an NHS dietitian, and that anyone seeing a private dietitian should check they are registered with the British Dietetic Association.

NICE sets a stepped order. Antispasmodics are considered alongside lifestyle advice, laxatives for constipation (with lactulose discouraged), and loperamide as the first-choice antimotility drug for diarrhoea. Low-dose tricyclic antidepressants are considered second line if those do not help, and SSRIs only if tricyclics are ineffective. NICE notes that at the time of publication these antidepressants had no UK marketing authorisation for IBS, and they are used at low doses specifically for pain rather than for mood.

The NHS describes the same idea: if pharmacy medicines do not help, a GP may prescribe a medicine such as amitriptyline or citalopram, which are antidepressants that can also ease IBS symptoms, take a few weeks to work and may cause side effects. For people whose symptoms persist, NICE suggests referral for CBT, hypnotherapy or psychological therapy after 12 months of non-response, and the NHS notes that adults can refer themselves directly to NHS talking therapies for CBT.

Not all complementary approaches are supported. NICE says acupuncture should not be encouraged, and the NHS suggests probiotics only as a one-month trial.