IBS and diverticular disease both involve the lower belly and bowel habits, so they are easy to confuse. Diverticulosis, which means small pouches in the wall of the colon, becomes very common with age: more than half of Americans over 60 have it.[1] It's the most common finding on routine colonoscopy, so many people with IBS hear about pouches by chance.[2] What matters is telling those harmless pouches apart from diverticulitis, an inflammation that needs prompt medical care.[3]
Diverticulosis, diverticular disease and diverticulitis: what's the difference?
| Term | What it means | Symptoms |
|---|---|---|
| Diverticulosis | Pouches (diverticula) in the colon wall | Usually none; often found by chance on colonoscopy[1][2] |
| Symptomatic uncomplicated diverticular disease | Ongoing gut symptoms in someone with diverticulosis, without signs of inflammation | Pain, bloating and bowel changes that overlap heavily with IBS; definitions vary and the diagnosis is controversial[1] |
| Acute diverticulitis | Inflammation of the diverticula | Belly pain coming on over hours to days, usually in the lower left; often fever, nausea, a change in bowel habit and raised inflammation markers[4] |
| Complicated diverticulitis | Diverticulitis with an abscess, perforation, narrowing (stricture), blockage or fistula[1] | Needs urgent assessment |
Only a small minority of people with pouches ever get diverticulitis. Older estimates put the lifetime risk at 10% to 25%, but modern estimates based on colonoscopy and CT scans suggest fewer than 5%.[1] In a study of 2,222 US veterans whose diverticulosis was found on colonoscopy, 4.3% developed diverticulitis over 11 years.[2]
IBS vs diverticulitis: how do the symptoms differ?
| IBS | Acute diverticulitis | |
|---|---|---|
| Pain pattern | Recurrent, on average at least one day a week for months, and linked to bowel movements[5] | A distinct episode that comes on over hours to days, most often in the lower left abdomen[4] |
| Fever | No; fever is a warning sign that points away from IBS[6] | Common, as is nausea[4] |
| Blood tests | Normal[7] | White cell count and C-reactive protein (CRP) are often raised[4] |
| Course | Long-term: symptoms for at least the past 3 months, starting 6 or more months before diagnosis[5] | An attack that can come back: about 20% of people have at least one recurrence[1] |
| Confirmed by | Symptom criteria plus a few normal tests[5][7] | CT scan, especially for a first episode[3] |
Symptoms alone are a poor guide, even for doctors: a clinical suspicion of diverticulitis turns out to be right in only 40% to 65% of cases, which is why a CT scan is usually needed to confirm it. Rarely, colon cancer is mistaken for diverticulitis.[4]
IBS vs diverticulosis: can the pouches cause IBS-type symptoms?
Diverticulosis on its own usually doesn't cause symptoms. Some people with diverticulosis have ongoing pain and bloating without inflammation, a pattern called symptomatic uncomplicated diverticular disease. But its symptoms overlap so much with IBS that experts disagree about whether it's a separate condition.[1]
Diverticulitis, on the other hand, can leave IBS-type symptoms behind. In one trial, about 45% of people still had periodic belly pain a year after an uncomplicated episode.[4] In a study of US veterans, those who had had diverticulitis were 4.7 times as likely to be diagnosed with IBS later, a pattern the researchers called post-diverticulitis IBS.[8] If symptoms persist after diverticulitis, the American Gastroenterological Association (AGA) advises imaging and a colonoscopy to rule out ongoing inflammation first. If none is found, an oversensitive gut, as in IBS, is the likely cause.[4]
What helps, and do you need to avoid nuts and seeds?
- No need to avoid nuts, seeds, corn or popcorn. The American College of Gastroenterology (ACG) says a healthy diet that doesn't avoid these foods, regular physical activity, a healthy weight, not smoking, avoiding heavy drinking and limiting anti-inflammatory painkillers (NSAIDs) where possible may help keep diverticulitis from coming back.[3]
- Fiber, chosen for IBS. For IBS symptoms, soluble fiber such as ispaghula (psyllium) helps, while insoluble fiber such as wheat bran can make symptoms worse. Start with a small dose and build up slowly to avoid bloating.[7]
- During an uncomplicated attack, a clear liquid diet is advised at first, with a gradual return to normal food as symptoms improve.[4]
- Antibiotics aren't always needed. The ACG suggests against routine antibiotics for low-risk, uncomplicated diverticulitis, but they're appropriate for people with high-risk features, weakened immunity or frailty.[3]
If IBS is your main problem, the usual IBS approaches apply, including a dietitian-led low-FODMAP diet.
When to see a doctor
Get medical care the same day for new belly pain that keeps building over hours, especially in the lower left, or belly pain with fever or nausea. These are typical signs of diverticulitis, and a scan is often needed to confirm it.[4] Go to an emergency department for severe pain, a hard or very tender belly, a high fever, heavy bleeding from the rectum, or vomiting that stops you keeping fluids down. Complications such as an abscess or a perforation need urgent treatment.[1]
See your doctor soon, too, for any IBS warning sign: blood in your stool, unintentional weight loss, anemia, symptoms that wake you at night, a family history of bowel cancer, inflammatory bowel disease or celiac disease, or symptoms that started after about age 50.[6][7] After an episode of diverticulitis, a colonoscopy is recommended if it was complicated, and suggested if you have alarm symptoms or aren't up to date with colorectal cancer screening.[3] More in IBS red flags and IBS or colon cancer.
Between visits, note where the pain is, whether a bowel movement eases it, whether you feel feverish, and your stool type. Recurring pain that's tied to bowel movements fits IBS; a new attack of building pain with fever doesn't. IBS Clue's symptom check-ins and Bristol stool log can keep that record and export it as a report for your doctor.