Irritable Bowel Syndrome (IBS)

What happens in IBS

IBS is not caused by structural damage. Instead, several mechanisms combine:

• gut-brain axis changes: the brain and gut communicate abnormally, so normal gut activity is felt as pain
• visceral hypersensitivity: the gut's nerves are more sensitive to stretching and gas
• altered gut motility: contractions are too fast (diarrhea) or too slow (constipation)
• changes in gut bacteria
• low-grade immune activation in the gut lining
• post-infectious IBS: about 1 in 10 people develop IBS after a bout of gastroenteritis

Stress does not cause IBS by itself, but it strongly influences symptoms through the gut-brain axis.

Symptoms

• cramping belly pain, often in the lower belly, that is related to bowel movements, either improving or worsening
• change in how often you have bowel movements
• change in stool form, from hard lumps to loose or watery
• bloating and visible abdominal distention, often worse through the day
• excess gas
• mucus in the stool
• urgency, or a feeling of incomplete emptying

Many people also have fatigue, back pain, headaches, heartburn, urinary frequency, and conditions such as fibromyalgia, chronic fatigue syndrome and anxiety or depression.

Types of IBS

Diagnosis

Rome IV criteria

Recurrent abdominal pain on average at least 1 day per week in the last 3 months, associated with two or more of:

• related to defecation
• a change in stool frequency
• a change in stool form

Symptoms should have started at least 6 months before diagnosis.

Tests to rule out other conditions

Doctors use a positive diagnosis strategy rather than extensive testing:

• blood count for anemia
• celiac disease antibodies for IBS-D and IBS-M
• C-reactive protein and fecal calprotectin to screen for inflammatory bowel disease in diarrhea
• stool tests for Giardia in some cases
• colonoscopy if red flags are present, or for age-appropriate cancer screening

Conditions that mimic IBS

Treatment

Diet and lifestyle

• Regular meals, eaten slowly. Avoid large, fatty meals.
• Soluble fiber such as psyllium helps both constipation and overall symptoms. Insoluble fiber such as wheat bran can worsen bloating.
• Low-FODMAP diet: FODMAPs are fermentable carbohydrates found in foods such as wheat, onions, garlic, beans, some fruits and lactose. A dietitian-led plan has three phases: elimination for 2 to 6 weeks, reintroduction to find triggers, and personalization. It improves symptoms in more than half of people.
• Limit caffeine, alcohol, fizzy drinks and sugar-free sweeteners (sorbitol, mannitol).
• Exercise regularly, which improves symptoms and mood.
• Peppermint oil capsules can ease pain and bloating. Follow the label dose. They can worsen heartburn.

Gut-brain therapies

• cognitive behavioral therapy and gut-directed hypnotherapy have strong evidence and lasting benefits
• stress reduction, mindfulness and better sleep

Medicines

• antispasmodics (such as dicyclomine or hyoscyamine) for cramping
• low-dose tricyclic antidepressants (such as amitriptyline) act as gut nerve pain modulators, especially helpful in IBS-D and pain-predominant IBS
• SSRIs in some patients, particularly with anxiety or depression
• IBS-D: loperamide for diarrhea, rifaximin (a non-absorbed antibiotic), eluxadoline, and bile acid binders
• IBS-C: polyethylene glycol, linaclotide, plecanatide, lubiprostone and tenapanor

Probiotics have mixed evidence. If you try one, give it about 4 weeks and stop if there is no benefit.

Living with IBS

IBS tends to come and go, with flares and calmer periods. A symptom and food diary helps identify personal triggers. Planning, such as knowing restroom locations, can reduce anxiety about urgency. Many people find a combination of diet, therapy and medicine gives good control.

IBS does not raise the risk of colorectal cancer, inflammatory bowel disease or other serious bowel disease, and it does not shorten life.

Frequently asked questions

What are the main symptoms of IBS?

The main symptoms are recurring belly pain related to bowel movements, changes in stool frequency or consistency, bloating, gas and mucus in the stool. People may have mostly diarrhea, mostly constipation, or alternate between them.

What triggers IBS flare-ups?

Common triggers include certain foods (high-FODMAP foods like onions, garlic, wheat, beans and some fruits, plus fatty meals, caffeine and alcohol), stress, poor sleep, menstrual cycle changes and gut infections. Triggers vary between people, so a food and symptom diary helps.

What is the difference between IBS and IBD?

IBS is a disorder of gut function without visible damage, causing pain and altered bowel habits. Inflammatory bowel disease (Crohn's disease and ulcerative colitis) involves inflammation that damages the bowel, often with bleeding, weight loss and raised inflammatory markers. IBD needs different treatment.

Does the low-FODMAP diet work for IBS?

Yes, for many people. Studies show more than half of people with IBS improve on a low-FODMAP diet. It is meant to be followed in phases, ideally with a dietitian: a short elimination period, then reintroducing foods to find personal triggers, so the diet is not overly restrictive long term.

Can IBS be cured?

There is no permanent cure, but IBS can usually be well controlled. Symptoms often improve over time, and many people have long periods with few symptoms. Diet changes, gut-directed psychological therapies and targeted medicines are effective.

Is IBS dangerous?

No. IBS does not damage the bowel, cause cancer or shorten life. However, red flags such as rectal bleeding, weight loss, anemia or night-time symptoms are not typical of IBS and need medical assessment.