Diverticular disease

What is the difference between the three words

They mean different things, and the difference is the whole point.

• Diverticulosis means small pouches have formed in the wall of the colon. On its own it causes no symptoms and needs no treatment. It is the commonest finding at colonoscopy
• Diverticular disease is the term used when those pouches cause symptoms. It covers everything from ongoing discomfort without inflammation through to an acute attack
• Diverticulitis means one or more of the pouches has become inflamed or infected. This is the one that causes pain and fever and occasionally needs hospital care

It is strongly age-related, and commoner at every age than most people expect. In a study of people having a first screening colonoscopy, about a third of those aged 50 or under had at least one diverticulum, rising to around six in ten of those over 60. In large national endoscopy records the figure reaches roughly seven in ten people over 80. Older textbook figures put the numbers much lower, but they come from the days before routine colonoscopy. The pouches form where small blood vessels pierce the bowel wall and leave it naturally weaker, and pressure inside the colon pushes the lining out through those points.

What the risk actually is

This is the part most often misunderstood, including in older patient information. Three different numbers get quoted as though they answer the same question, and they do not.

Guidelines used to quote a lifetime risk of developing diverticulitis of 10 to 25 per cent, which is frightening and, it turns out, was based on data collected before colonoscopy was widespread, when only the people who became unwell were ever counted.

A study of 2,222 people whose diverticulosis was found incidentally at colonoscopy, followed over an eleven-year period, showed that 4.3 per cent developed acute diverticulitis, and 1 per cent when a stricter definition was used. The median time to an episode was just over seven years. The A second study that followed people for an average of seven years found almost the same thing, with about 4 in 100 developing diverticular disease. Across a whole lifetime the American College of Gastroenterology's 2026 guideline puts the risk at about 3 to 5 per cent, and tells patients that most older adults have diverticulosis but only a small minority ever develop diverticulitis.

A larger proportion, around 20 to 25 per cent, develop symptoms of some kind that are put down to the pouches. That is a different and much broader endpoint, and most of that group have discomfort, bloating or a change in bowel habit rather than an acute attack.

In other words, for most people a report that says diverticulosis is a description rather than a diagnosis, and the chance of it ever causing serious trouble is small.

If you have already had an episode

The arithmetic changes once diverticulitis has happened, and it is worth knowing honestly. About two in ten people have a second episode within ten years of the first. After a second episode the chance of a third rises to around five in ten. Once someone has had several attacks, further ones remain likely.

The reassuring part sits alongside it. The risk of a complication is highest at the very first presentation and falls with later recurrences, so a repeat attack is generally less dangerous than the one before it rather than more. Needing a permanent colostomy is very unlikely.

Age cuts in both directions here, and the averages above hide it. The younger someone is when diverticulosis or a first attack is found, the more likely they are to have an episode at all and the more likely it is to come back: each additional decade of age at diagnosis lowered the risk of developing diverticulitis by about a quarter in one study, and recurrence fell with age in another. Against that, younger people tend to have less severe episodes, fewer complications and better survival. So someone diagnosed in their forties should read the recurrence figures as an underestimate and the complication figures as an overestimate.

What a flare feels like

Diverticulitis usually announces itself as pain in the lower left side of the abdomen that builds over a day or two and stays put, rather than the crampy pain that comes and goes with irritable bowel syndrome. Fever, nausea and a change in bowel habit often come with it. Some people feel unwell before the pain settles in one place.

In a population study of diverticulitis, 88 per cent of people presented with the uncomplicated form, meaning inflammation confined to the bowel wall without an abscess, a perforation, a narrowing or a connection to another organ. The clinical picture alone is not accurate enough to tell the two apart, which is why a CT scan is used to confirm the diagnosis, particularly at a first presentation.

Diverticular bleeding is a separate event. It is painless, it can be sudden and surprisingly heavy, and it usually stops by itself. It is one of the causes of rectal bleeding and, because of the volume, it is one that often brings people to an emergency department.

How diverticulitis is treated

Mild diverticulitis is often managed at home, with rest, fluids, pain relief and a lighter diet for a few days while symptoms settle. Some people find clear fluids for the first day or two more comfortable. That is about comfort rather than healing, and there is no evidence it makes the inflammation settle faster.

Antibiotics are no longer automatic

Antibiotics were once given to everyone. Four randomised trials involving more than 1,800 patients with mild, left-sided, uncomplicated disease have since been pooled, and antibiotics made little or no difference to survival, to progression to complicated disease, to the need for surgery, to readmission or to recurrence. The 2026 American College of Gastroenterology guideline now suggests against routine antibiotics in low-risk patients with acute uncomplicated diverticulitis.

That is a suggestion about a selected group, not a rule for everyone. Antibiotics remain appropriate where there are high-risk features, where the immune system is suppressed, in frailty and where someone cannot safely be managed at home. A small number of people go on to develop a complication such as an abscess or a perforation, fewer than 1 in 20 over the following year, and when it happens it is usually in the first weeks rather than months later. That is why the first fortnight is the period to watch.

Hospital care is needed when the pain is severe, when fluids will not stay down, when there is a high fever or when a scan shows a complication. The complications are uncommon and include an abscess, a perforation, a connection forming to another organ and narrowing of the bowel from repeated inflammation.

The colonoscopy afterwards

A colonoscopy after recovery is not done for the diverticulitis. It is done because bowel cancer can present in exactly the same way and be misread as an attack. Across 19 studies the rate of colon cancer found after a first diagnosis of diverticulitis was 1.6 per cent, but that risk is not spread evenly. After complicated disease the odds of colon cancer were around six times higher, while after uncomplicated disease the risk was no different from the general screening population.

So a colonoscopy is recommended after an episode of complicated diverticulitis. After an uncomplicated episode it is not automatic, but it can reasonably be considered, and a first episode is the usual point at which it is offered. The case for it is strongest where someone is not up to date with bowel cancer screening or has alarm features such as unintended weight loss, a change in bowel habit, iron deficiency anaemia, blood in the stool or pain that does not settle. It is not performed within six to eight weeks of the attack, because inflammation and swelling make the examination harder and less safe. A recent colonoscopy may mean it is not needed at all.

Surgery

Surgery is reserved for complications and for people whose repeated episodes are genuinely disrupting life. Removing the affected segment reduces recurrence without abolishing it: in the randomised trial of people already being considered for an operation, meaning those with repeated or persistent disease, about six in ten had another episode within two years without surgery against about one in ten after an operation. Recurrence after that operation is uncommon, in the order of one in twenty. Those figures are much higher than the ones quoted earlier for people after a first episode, because it is a different and far more affected group. Modern practice weighs how much the episodes are costing someone rather than counting them, and the decision is made together with a colorectal surgeon.

One thing that is not recommended is taking something long term to prevent the next attack. Probiotics have been looked at and are not recommended for this purpose, and the two prescription medicines most often tried for it are both advised against in the 2026 guideline.

What about diet, and the nuts and seeds question

For decades people with diverticulosis were told to avoid nuts, seeds, corn and popcorn, on the theory that fragments lodged in the pouches. It was advice given confidently and it was never tested.

It has been now. A study of 47,228 men followed for 18 years found that eating nuts, corn and popcorn did not increase the risk of diverticulitis or diverticular bleeding. Nuts and popcorn were in fact associated with a lower risk of diverticulitis. The authors concluded the advice to avoid these foods should be reconsidered, and guidelines have since dropped it.

What does appear to matter is the opposite of restriction. In the EPIC-Oxford study vegetarians had a 31 per cent lower risk of diverticular disease than meat eaters, and people in the highest fifth for fibre intake had a 41 per cent lower risk than those in the lowest. The pattern that comes out of the dietary work is a familiar one: plenty of fruit, vegetables, wholegrains and legumes, with less red meat, processed grain, unhealthy fat and sugar. Fibre from food does the work here. Supplements are not a substitute for the diet itself.

The other things with evidence behind them

• Smoking. Current smokers have around a 36 per cent higher risk of diverticular disease serious enough to require hospital admission, and roughly two and a half times the risk of the complicated form.
• Weight. Being overweight or obese raises the risk, and weight loss is suggested for people who have had an episode.
• Activity. Regular physical activity is associated with a lower rate.
• Alcohol. Heavy intake raises the risk. Moderation is the advice rather than abstinence.
• Anti-inflammatory painkillers. Regular use of non-aspirin anti-inflammatories was associated with about a 70 per cent higher risk of a first episode of diverticulitis. The guideline suggests avoiding regular use after recovery unless there is a clear reason for them. If they were prescribed for something like arthritis, that is a conversation with the doctor who prescribed them rather than a reason to stop on your own. Paracetamol is not in this group.

During an acute flare a lower-fibre diet for a few days is easier on the bowel, and fibre is built back up gradually once things settle. Going back to a high-fibre intake too quickly after an attack can itself cause cramping. That short-term measure is different from a permanent restriction.

What if you have just been told you have diverticulosis

Practically, for most people this is what it means.

• No treatment and no medication are needed for the pouches themselves. The one thing not to leave alone is constipation, if you actually have it. That is managed on its own merits
• No repeat colonoscopy is needed just to look at them. Your surveillance interval is set by whatever else was found, such as polyps
• No foods need avoiding, and a good fibre intake is worth working towards
• Know the warning signs. Persistent pain low on the left with fever is worth being seen for promptly

Ongoing symptoms without inflammation, sometimes called symptomatic uncomplicated diverticular disease, do occur and overlap heavily with irritable bowel syndrome. Where that is the picture, the treatment follows the IBS approach rather than repeated courses of antibiotics.

The same thing happens after an attack. More than a third of people are left with ongoing bowel symptoms one to two years after an episode of diverticulitis, most often bloating, wind, a feeling of fullness and more frequent stools, and being told the scan is now normal does not make that go away. It is common, it is recognised in the guidelines and it usually responds to the approach used for disorders of gut-brain interaction rather than to further antibiotics or further scans.

Where diverticular disease is assessed in Sydney

A/Prof Viraj Kariyawasam is a consultant gastroenterologist and hepatologist. Diverticulosis found at colonoscopy, and recovery after an episode of diverticulitis, are assessed at consultation in Norwest, Rouse Hill, Pennant Hills and Macquarie Park.

Where a colonoscopy is needed, it is performed at Norwest Private Hospital, Macquarie University Hospital and Pennant Hills Day Surgery. A referral from your GP is needed for a consultation.