What Causes Diverticular Disease?

Why Do Members Find The Causes So Confusing?

Members regularly ask this question, and they often receive conflicting answers. One member opened the discussion that this article draws on with a simple request.

“Why do we get the pockets? What causes them?”

Beverley, Cardiff

The replies showed how little agreement exists, even among clinicians. Two members described opposite statements from their own surgeons within the same thread. One reported that her colorectal surgeon rejected the idea that anything gets stuck in the pouches.

“The colorectal surgeon I saw said the stuck items theory is false. He has operated on hundreds of people and has never found anything stuck in the diverticula.”

Carla, Brisbane

Another member reported the reverse from her own surgeon.

“My surgeon literally said it’s food.”

Denise, Ohio

A third member summed up the frustration that many newly diagnosed people describe.

“A lot of speculation going on, even the gastroenterologists aren’t sure the cause.”

Keith, Phoenix

Another member questioned how food could lodge in a pouch at all.

“How can food get lodged in the diverticula? Honest question because I am truly confused.”

Margaret, Vancouver

This confusion has a clear source. The leading review behind this article says researchers understand the development of diverticulitis only incompletely and describes that understanding as superficial. The sections below separate what research has established from what remains a theory.

How Do Pouches Form In The Colon Wall?

Pouches form at natural weak points in the colon wall. According to the StatPearls chapter on  diverticular disease, a diverticulum forms where small blood vessels (the vasa recta) pass through the muscle layer. When pressure builds inside a stretch of colon that does not move contents along well, the inner lining bulges out through that gap.

Three further findings explain where and why this happens.

• • In the United States and Western Europe, up to 90% of cases sit exclusively in the sigmoid colon, the final curved section before the rectum. The sigmoid is less stretchy than the rest of the colon. The rectum, which is highly stretchy and has an extra layer of muscle, does not develop diverticula (Strate and Morris).
  • Connective Pouches appear early in life in people with connective tissue disorders such as Marfan syndrome, Ehlers-Danlos syndrome and polycystic kidney disease. Researchers have also found changes in collagen in the colon wall of people with diverticulosis.
  • Nerves and movement. Studies report fewer nerve cells and imbalances in chemical messengers such as serotonin in the colon wall of people with diverticular disease. Researchers do not yet know whether these changes come before the pouches or result from

Age also plays a role. One member with a long-standing diagnosis described the pattern in plain terms.

“40-50% of elderly have pockets but most have no flare ups or symptoms. I suppose one could say in that respect it’s general wear, but genetics can play a part.”

Colin, Kent

Rates of diverticulitis are also rising in younger adults. Strate and Morris cite a population study in which diverticulitis in people aged 40 to 49 increased by 132% between 1980 and 2007. Our guide on what age people get diverticulitis covers the age pattern in more detail.

Does Constipation Or A Low Fibre Diet Create The Pouches?

The long-held answer was yes, but the evidence no longer supports a simple version of that answer. The idea dates to the mid-twentieth century. It proposed that a low-fibre diet produces small, hard stools, raises pressure in the colon and forces the lining through weak spots. The NHS still states that people are more likely to develop diverticular disease and diverticulitis if they do not eat enough fibre.

A colonoscopy study led by Dr Anne Peery, published in Gastroenterology in 2012 with a follow-up paper in Clinical Gastroenterology and Hepatology, tested that idea directly. The team compared 539 people who had diverticulosis with 1,569 who did not. Constipation was not associated with an increased risk of pouches. People with fewer than seven bowel movements a week had lower odds of diverticulosis, not higher. Straining and incomplete emptying showed no association, and fibre intake showed none either (odds ratio 0.96 comparing the highest and lowest quarters). The lead researcher said more research was needed before doctors change dietary recommendations.

Two limits apply to that study. It was cross-sectional, so it captured one moment in time. It examined asymptomatic diverticulosis, meaning pouches found at colonoscopy, and did not examine diverticulitis. For inflammation, the picture differs: Strate and Morris report that people in the highest fifth for fibre intake had a relative risk of diverticulitis of 0.57 to 0.75 compared with the lowest fifth, a lower risk.

That split matters for members, because the same word, “causes”, covers two separate questions. The table below sets member experiences beside the research.

Member accounts illustrate both sides. One member traced her condition to a lifelong bowel pattern.

“The cause of mine is underdeveloped bowels and a lifetime of constipation.”

Wendy, Melbourne

Others described the opposite pattern and pointed to family history instead.

“I’ve never had constipation. Actually the opposite. Have had diverticulosis since my 30s and just had my sigmoid removed. More to it than that. Ie bad genes.”

Martin, Sheffield

“I rarely get constipation and I get flares.”

Sandra, Texas

Individual accounts do not settle the question for anyone else, and research on pouch formation continues. Our members also report that doctors give them different advice on fibre, which is why we recommend speaking to your own clinician about your own bowel pattern.

How Much Do Genes And Family History Matter?

Genes matter more than most members expect. Two large Scandinavian twin and family studies estimated that genetic factors account for 40% to 50% of the risk of diverticular disease (Strate and Morris). Identical twins showed higher shared risk than non-identical twins, and siblings showed higher shared risk than the general population. The NHS states that people with a close relative who has the condition, especially one who developed it before 50, are more likely to develop diverticula.

Large genetic studies have started to identify specific genes. A genome-wide study in Iceland and Denmark linked variants in three genes (ARHGAP15, COLQ and FAM155A) with diverticular disease. A UK Biobank study of about 28,000 hospital admissions found 42 risk locations in the genome and confirmed the same three genes. These genes regulate immune function, the structure between cells, and gut movement. A sibling with the condition raises the relative risk of diverticular disease to 2.92 in the studies Strate and Morris reviewed.

Several members describe exactly this family pattern.

“Have had it for over four decades. Multiple people on both sides of my family have it and have had surgeries. Don’t know what caused it. Seems to be a genetic predisposition.”

Maureen, Adelaide

Another member who follows a long-standing high-fibre diet reached a similar view after her own diagnosis.

“My lifelong high fibre Mediterranean diet with fermented foods did NOT prevent my diagnosis. The strongest evidence on causation appears to be genetics plus ageing.”

Peter, Bristol

A genetic influence does not remove other influences. Strate and Morris describe diverticulitis as arising from an interaction of diet, lifestyle, medicines, genes and the gut microbiome.

What Turns Pouches Into Diverticulitis?

Inflammation turns a pouch into diverticulitis, and researchers now favour a broader explanation than a simple blockage. For decades, doctors taught that stool blocks the neck of a pouch, bacteria multiply behind the blockage, and the wall becomes inflamed and develops tiny tears. The StatPearls chapter still calls this the presumed cause but notes that recent studies have challenged it. Strate and Morris describe the theory as long-standing but unproven.

Three lines of evidence drive the newer thinking.

• • Antibiotic Two large randomised trials, one in Sweden and Iceland (623 patients) and one in the Netherlands (570 patients), found that antibiotics did not speed recovery or prevent complications in uncomplicated diverticulitis. Those findings pushed researchers towards models that involve inflammation as well as infection. Your doctor decides whether antibiotics suit your situation.
  • Chronic inflammation. Many risk factors for diverticulitis, including obesity, inactivity and a Western diet, also drive long-term low-level inflammation in the body. The evidence is indirect. One study of more than 600 people having screening colonoscopies found no link between pouches alone and markers of inflammation, so pouches by themselves may not be
  • Gut bacteria. Studies report that the mix of gut bacteria differs between people with and without diverticulitis, including fewer bacteria that produce short-chain fatty acids, which help protect the gut lining. Researchers cannot yet say whether these differences cause the illness or follow it, because diet changes and antibiotics after diagnosis also alter gut

Some members continue to have symptoms after an episode has passed. Strate and Morris report that about 40% of people with scan-confirmed diverticulitis in one trial still had mild to moderate pain or bowel changes a year later. They also report that, in a large study of US veterans, people with a history of diverticulitis had a fivefold higher risk of irritable bowel syndrome. Researchers keep studying why.

Is It Food, Stool Or Something Else Stuck In The Pouches?

The most heated debate in our group concerns what, if anything, gets stuck in a pouch. Members offered three different answers, and each member described the answer as settled. The research does not.

One member shared a theory he tested on himself over many years. He reported that thoroughly chewing foods he had previously avoided stopped his flare-ups.

“I have always eaten too fast. Was my diverticulitis caused by improperly chewed food?”

Graham, Leeds

Other members disagreed and described a different mechanism.

“It’s old hard poop that is stuck in a pocket/pouch that then causes inflammation/infection.”

Pauline, Norwich

Not every member who chewed carefully avoided complications, which shows how individual the picture is.

“I had been chewing small bites well but still ended up with a colectomy.”

Gillian, Calgary

One older belief now has strong evidence against it. Doctors once told people with pouches to avoid nuts, seeds and popcorn. A large prospective study found these foods do not raise the risk of diverticulitis, and nuts and popcorn were linked with lower risk (Strate and Morris; StatPearls).

Many members still avoid them because of how their own bodies react. Our article on whether food triggers diverticulitis covers those personal food experiences in depth, and this article deliberately keeps to the medical mechanisms.

Which Medicines And Health Conditions Raise The Risk?

Several common medicines show a consistent link with diverticulitis in large studies. These studies are observational, so they show an association and do not prove that the medicine caused the illness. The table gives the relative risk Strate and Morris report, where 1.0 means no change in risk and 2.0 means double the risk.

Strate and Morris also report that NSAIDs link more strongly with complicated or perforated diverticulitis than with uncomplicated disease. Higher vitamin D levels link with lower risk (relative risk 0.49 in the highest fifth). Immune suppression, whether from steroids or other causes, raises the chance of more serious disease. StatPearls also lists high blood pressure, type 2 diabetes and connective tissue disorders among the associated conditions.

One member described how this plays out when a person needs a medicine for another condition.

“My trigger is steroids, prednisone, that I need to take [for another condition], and I can’t have ibuprofen either. Doctors state both drugs are triggers.”

Janice, Wellington

People who take any of these medicines for another condition should speak to their GP, pharmacist or specialist before changing anything.

Which Lifestyle Factors Change The Risk?

Lifestyle factors shift the odds of diverticulitis without causing it on their own. Strate and Morris pooled large cohort studies and report the following relative risks for diverticulitis.

One study combined five factors: fewer than four servings of red meat a week, at least 23 grams of fibre a day, two hours of vigorous activity a week, a body mass index of 18.5 to 24.9, and no smoking history. People who followed all five had nearly 75% lower risk of diverticulitis. If the links are causal, the authors estimate that such a lifestyle could prevent half of all cases.

The effect of any single factor on any single person remains uncertain. Our members also report that stress, which sits outside the medical causes covered here, shapes their symptoms, and we cover that in Can Stress Trigger Diverticulitis Symptoms?. For what members say sets off a flare once the condition exists, read What Triggers Diverticulitis Flare Ups?.

Why Do Some People With Pouches Never Develop Diverticulitis?

Nobody can yet predict who will move from pouches to inflammation. Strate and Morris list markers of risk and the reasons behind the rapid rise in younger patients among the unanswered questions. Members notice the gap too.

“Very little is known why some people with diverticulosis never get diverticulitis.”

Imran, Birmingham

The numbers give some reassurance and some context. About 96 in every 100 people with diverticulosis never develop diverticulitis. One member reacted to that figure with concern for newly diagnosed readers.

“Interesting that only 4% of people with diverticulosis get diverticulitis!”

Alison, Edinburgh

A fair reading of the figure recognises both sides. Most people with pouches never develop inflammation, and our group naturally attracts the minority who do. That selection explains why the group can seem to describe the condition as more common and more severe than it is for the average person with pouches.

What Does The Inflammation Stage Look Like In Practice?

Diverticulitis ranges from a mild episode to an emergency. Complications such as an abscess, a hole in the bowel wall (perforation), a blockage or an abnormal passage (fistula) occur in about 12% of people with diverticulitis, and they happen more often at the first episode than at later ones (Strate and Morris). One member learned she had the condition only when it became an emergency.

“I did not realize that I had diverticulitis until this happened. So now I am very afraid of it getting way out of hand before I realize that I’m having a flare.”

Fiona, Perth

Her fear is common among our members. The NHS advises contacting a GP as soon as possible if you have symptoms of diverticular disease or diverticulitis. Our ultimate guide to diverticulosis and  diverticulitis explains the symptoms and the stages in more detail.

How Does This Article Differ From Our Other Causes Pages?

Each of our causes articles answers a different question. Use this table to find the one that matches yours.

Frequently Asked Questions

Can Eating Too Much Bread At One Sitting Cause Diverticula?

No source reviewed for this article reports that a single large meal creates pouches. One member shared that this was his belief about the start of his own condition, and another member asked how he could know. Researchers attribute pouch formation to ageing, genes, connective tissue and gut movement, not to one meal.

Is Diverticular Disease Hereditary?

Partly. Twin studies attribute 40% to 50% of the risk to genetic factors, and the NHS states that a close relative with the condition raises your chance of developing diverticula, especially if the relative developed it before 50. Genes do not decide the outcome on their own.

Can Younger People Develop Diverticular Disease?

Yes. Diverticulosis becomes more common with age, but Strate and Morris report that the fastest rise in diverticulitis over recent decades occurred in younger people. StatPearls reports that hospital admissions for diverticular disease in the United States rose by 32% between 1997 and 2018.

Is Diverticulitis Always Caused By An Infection?

Researchers no longer treat it as purely an infection. The two large antibiotic trials found no faster recovery with antibiotics in uncomplicated cases, which pushed researchers towards models that involve inflammation as well as infection. Bacteria still play a part when a pouch tears and infection follows, as in an abscess. Only your doctor can say which applies to you.

Do Nuts, Seeds And Popcorn Cause Diverticulitis?

A large prospective study found that nuts, seeds and popcorn do not raise the risk of diverticulitis. Individual members still report symptoms after eating them, and our food article explores those reports.

Can You Prevent Diverticular Disease?

Nobody can guarantee prevention. The NHS states that eating a high-fibre diet may help ease symptoms and stop diverticulitis developing. Strate and Morris report that a combination of lifestyle factors lowered risk by nearly 75% in one large study, and they also list the role of diet and lifestyle in preventing recurrence as an area that needs more research. Discuss your own situation with your GP.

More Reading

Does Food Trigger Diverticulitis? What Our Community’s Experience Reveals

What Triggers Diverticulitis Flare Ups?

Halloween And Diverticulitis: What You Can Eat, What To Watch And Easy Swaps

What Causes Diverticulitis?

Can Stress Trigger Diverticulitis Symptoms?

Key Takeaways

• • Diverticular disease has no single proven cause, and pouch formation and inflammation have different explanations.
  • Pouches form at weak points in the colon wall, most often in the sigmoid colon, and ageing, genes and connective tissue all contribute.
  • A colonoscopy study led by Dr Anne Peery found no link between constipation or fibre intake and pouch formation, while other research links higher fibre intake with lower diverticulitis
  • Genes account for an estimated 40% to 50% of the risk, according to twin
  • Corticosteroids, opiates and NSAIDs show consistent links with diverticulitis in large
  • Fewer than 5% of people with diverticulosis develop diverticulitis, and researchers cannot yet predict who will.
  • Members hear contradictory explanations from clinicians, so bring your own questions to your own doctor.

Sources

• • Strate LL, Morris Epidemiology, Pathophysiology, and Treatment of Diverticulitis. Gastroenterology, 2019 (PMC6716971).
  • Bach K, Menon G, Goosenberg Diverticular Disease of the Colon. StatPearls, last updated May 2026.
  • Diverticular disease and diverticulitis.
  • Peery AF et al. A High-Fiber Diet Does Not Protect Against Asymptomatic Diverticulosis. Gastroenterology, 2012 (press summary). Peery AF et Constipation and a Low-Fiber Diet Are Not Associated With Diverticulosis. Clinical Gastroenterology and Hepatology.

Members who want to track their own patterns can start the Food And Symptoms Diary or join the conversation in our forums and our Facebook group. Reading what other members experience will not settle the science, but it shows you that you are not alone with the questions.

Disclaimer: This article does not constitute medical advice. Diverticulitis affects everyone differently. Always seek advice from a qualified medical practitioner about your own symptoms, diagnosis and treatment.