Diverticulitis develops when small pouches that have formed in the colon wall become inflamed or infected, and no single cause explains why it happens. Instead, the disease emerges from a pileup of risk factors: a low-fiber diet, excess visceral fat, physical inactivity, certain medications, genetic susceptibility, and structural changes in the colon that accumulate with age. The relative weight of each factor varies from person to person, which is partly why some people live with dozens of diverticula and never have a flare while others end up in the emergency room after their first episode.
How the Pouches Form and Why They Get Inflamed
Before diverticulitis can happen, diverticula have to exist. These marble-sized outpouchings develop at weak spots in the colon wall, typically where blood vessels penetrate the muscle layer. As the colon ages, its connective tissue changes. Research on affected tissue shows increased smooth-muscle thickness, altered collagen structure, and disrupted motility patterns in the colon wall.1Europe PMC. Structural Alterations in Diverticular Disease These structural shifts make the wall less flexible and more prone to ballooning outward under pressure.
Once diverticula form, several things can tip them toward inflammation. Retained stool inside the pouch can cause mechanical irritation. Fecaliths, which are hardened balls of fecal matter, can compress blood vessels and create local ischemia. Bacteria can then translocate through the weakened, oxygen-starved tissue, sparking infection.2PubMed Central. Morphologic Basis for Developing Diverticular Disease, Diverticulitis, and Diverticular Bleeding Tiny perforations in the pouch wall, sometimes microscopic, allow gut bacteria direct access to surrounding tissue. The body responds with inflammation, and that is what you feel as diverticulitis: pain, fever, and tenderness, usually in the lower left abdomen.
People with diverticular disease also show measurable changes in the nerve networks that control the colon. Compared to healthy tissue, the enteric nervous system in affected segments has reduced neuronal density and signs of gliosis, a type of nerve-support-cell overgrowth that reflects chronic injury.3PubMed. Diverticular disease is associated with an enteric neuropathy as revealed by morphometric analysis These nerve changes likely contribute to the abnormal colon contractions and motility problems seen in affected patients, creating a cycle where dysmotility raises pressure inside the colon, which promotes more pouch formation.
Fiber, Red Meat, and Dietary Patterns
Diet is the most studied modifiable risk factor, and the evidence on fiber is consistent. A meta-analysis of five large prospective cohort studies covering more than 865,000 participants found that each additional 10 grams of daily fiber was associated with a roughly 26% lower risk of diverticular disease, with no sign of a plateau: people eating 40 grams a day had about 58% lower risk compared to those eating around 7.5 grams.4PubMed Central. Dietary fibre intake and the risk of diverticular disease: a systematic review and meta-analysis of prospective studies Interestingly, not all fiber sources seem to matter equally. In a large prospective study, fiber from fruit and cereal grains was linked to lower diverticulitis risk, but fiber from vegetables was not.5PubMed Central. Intake of Dietary Fiber, Fruits, and Vegetables and Risk of Diverticulitis The reason for this difference is not fully understood, though it may relate to the types of soluble versus insoluble fiber each food group provides.
Red meat consumption pulls risk in the opposite direction. A study following tens of thousands of men found that those eating the most red meat had about 58% higher risk of diverticulitis compared to those eating the least, with risk climbing by roughly 18% per daily serving.6PubMed Central. Meat intake and risk of diverticulitis among men Even one serving a week appeared to nudge risk upward. The association was driven primarily by unprocessed red meat rather than processed varieties like bacon or hot dogs, which is the reverse of what you might expect given the usual nutrition narratives. A separate prospective cohort study confirmed that avoiding both processed and unprocessed red meat was associated with reduced diverticular disease risk.7PubMed Central. Lifestyle, genetic susceptibility, and risk of diverticular disease: a prospective cohort study
When researchers zoom out and look at overall eating patterns rather than individual foods, the same story holds. A Western dietary pattern, heavy in red meat, refined grains, and high-fat foods, was associated with about 55% higher diverticulitis risk compared to a prudent pattern rich in fruits, vegetables, and whole grains. The authors found that fiber and red meat intake accounted for most of that difference.8PubMed Central. Western Dietary Pattern Increases, and Prudent Dietary Pattern Decreases, Risk of Incident Diverticulitis in a Prospective Cohort Study
Visceral Fat Matters More Than Your Scale Weight
Obesity has long been linked to diverticulitis, but the picture is more specific than “being overweight raises your risk.” What seems to matter is where your body stores fat, not just how much you carry. A study using deep-learning analysis of CT scans found that people in the highest quartile of visceral fat had roughly double the risk of developing diverticulitis compared to those in the lowest quartile. That association held across all weight categories: thin people with a lot of visceral fat were still at elevated risk, and some heavier people with less visceral fat were not.9PubMed. Visceral Fat Quantified by a Fully Automated Deep-Learning Algorithm and Risk of Incident and Recurrent Diverticulitis Subcutaneous fat (the kind just under the skin) and skeletal muscle mass were not significantly associated with the disease.
A population-based case-control study from Mayo Clinic reinforced this finding from a different angle: while BMI was higher in diverticulitis patients overall, once researchers accounted for visceral and subcutaneous fat directly, BMI itself actually showed an inverse association with risk.10PubMed Central. Aging, Obesity, and the Incidence of Diverticulitis: A Population-Based Study In other words, BMI is a crude proxy that mixes up muscle, subcutaneous fat, and visceral fat into one number. Visceral fat, the kind wrapped around your organs deep in the abdomen, appears to be the real culprit. This fat is metabolically active and produces inflammatory signaling molecules that may prime the colon for trouble. Geographic data supports this too: in Japan, where right-sided diverticulitis is more common, visceral obesity was significantly more prevalent among patients with left-sided disease, the type that matches Western patterns.11PubMed Central. Visceral Obesity as a Risk Factor for Left-Sided Diverticulitis in Japan: A Multicenter Retrospective Study
Physical Activity as a Protective Factor
Exercise is one of the most consistent protective factors in the diverticulitis literature, but the benefit seems concentrated in vigorous activity. A large prospective study of men found that those in the highest quintile of total physical activity had a 25% lower risk of diverticulitis, but when the researchers separated vigorous from non-vigorous exercise, only vigorous activity showed a significant association, with a 34% risk reduction.12PubMed Central. Physical activity decreases diverticular complications A separate analysis of healthy lifestyle factors reported a similar finding: men in the highest quartile of vigorous physical activity had about a 27% lower risk.13PubMed Central. Adherence to a Healthy Lifestyle is Associated with a Lower Risk of Diverticulitis among Men
A study of runners found a dose-response relationship that was strikingly linear: each additional kilometer per day of running was associated with about a 6% risk reduction. Runners covering eight or more kilometers a day had nearly half the risk of those running less than two kilometers daily.14PubMed Central. Incident Diverticular Disease Is Inversely Related to Vigorous Physical Activity Running speed mattered independently: faster runners had lower risk even after adjusting for total distance, which suggests that the intensity of effort itself does something protective beyond simply burning calories and reducing body fat.
The mechanism likely involves several pathways. Vigorous exercise reduces visceral fat, improves colon motility and transit time (so stool moves through faster, creating less opportunity for pouches to fill and pressurize), and has anti-inflammatory effects through cytokine regulation. Casual walking, while good for many health outcomes, does not appear to move the needle on diverticulitis specifically.
Medications That Raise Risk
Several common drug classes are associated with diverticulitis, and particularly with its more dangerous complications like perforation. The strongest associations involve NSAIDs (like ibuprofen and naproxen), corticosteroids, and opioid painkillers. A case-control study found that NSAID use was linked to roughly a three- to four-fold increase in the odds of perforated diverticular disease, corticosteroid use raised the odds roughly six- to eight-fold, and opioid analgesics approximately doubled the odds.15PubMed. Anti-inflammatory drugs, analgesics and the risk of perforated colonic diverticular disease
A meta-analysis of case-control and cohort studies confirmed and extended these findings. NSAID use was associated with a three-fold increase in the odds of complicated diverticulitis, and aspirin use showed a more modest but still significant association.16PubMed. Non-steroidal anti-inflammatory drugs and acetylsalicylic acid increase the risk of complications of diverticular disease: a meta-analysis of case-control and cohort studies Aspirin also raised the risk of diverticular bleeding substantially. A large prospective cohort study found that regular aspirin users had a 25% higher risk of diverticulitis and a 70% higher risk of diverticular bleeding, while non-aspirin NSAIDs carried a 72% higher risk of diverticulitis.17Gastroenterology. Use of Aspirin or Nonsteroidal Anti-inflammatory Drugs Increases Risk for Diverticulitis and Diverticular Bleeding
The mechanisms are plausible. NSAIDs inhibit prostaglandins that protect the gut lining, making the mucosa more vulnerable to bacterial invasion. Corticosteroids suppress the immune response, which may allow small infections to progress unchecked. Opioids slow colonic transit, increasing the time stool sits in diverticula and raising intraluminal pressure. If you have known diverticular disease, these findings are worth discussing with your doctor, especially if you rely on any of these medications regularly.
Smoking, Alcohol, and Combined Lifestyle Risks
Smoking and alcohol each appear to contribute to diverticulitis risk, and they compound each other. A study of women found that those who had ever smoked and consumed at least 15 grams of alcohol per day (roughly one standard drink) had a 60% higher risk of diverticulitis compared to never-smokers who did not drink.18PubMed Central. Smoking and Alcohol Consumption and Risk of Incident Diverticulitis in Women The combination was worse than either exposure alone, which suggests the mechanisms are at least partly independent. Smoking damages blood vessels and impairs microcirculation in the colon wall, potentially worsening the ischemia that drives inflammation in diverticula. Alcohol has its own effects on gut permeability and the microbiome.
When researchers have looked at overall healthy lifestyle adherence, combining high fiber intake, low red meat, vigorous exercise, healthy weight, and not smoking, the combined effect is substantial. Each additional healthy behavior stacks risk reduction, and men following all five factors have dramatically lower diverticulitis rates than those following none.13PubMed Central. Adherence to a Healthy Lifestyle is Associated with a Lower Risk of Diverticulitis among Men This is worth knowing because it means the disease is not simply a consequence of aging: a large fraction of cases are driven by lifestyle factors that are, at least in principle, changeable.
Genetic Susceptibility
For a disease long attributed almost entirely to diet and aging, diverticular disease turns out to have a surprisingly strong genetic component. Twin studies suggest that heritable factors account for a significant portion of individual risk.19PubMed Central. Genetic Risk Factors for Diverticular Disease-Emerging Evidence A large genome-wide association study estimated that the heritability of diverticular disease is about 40%, based on sibling-pair analysis. That same study, which included over 700,000 individuals, identified 150 independent genetic variants associated with the condition.20Cell Genomics. Genome-wide association analyses and post-GWAS analyses of diverticular disease of intestine An earlier, smaller genome-wide study had already found 42 significant loci, 39 of them newly identified at the time.21PubMed Central. Genome-wide association analyses identify 39 new susceptibility loci for diverticular disease
Many of the implicated genes relate to connective tissue structure, collagen formation, and smooth-muscle function, which makes sense given that the disease fundamentally involves weak spots in the colon wall. Others point to immune regulation. Genes like ARHGAP15 affect phagocyte function and inflammation, while variants in PHGR1 may promote epithelial dysfunction that lets bacteria penetrate the gut wall more easily.22BJS Open. Genetic, epigenetic and environmental factors in diverticular disease: systematic review The upshot is that some people are genetically wired to have weaker colon walls and more reactive immune systems in the gut, making them more susceptible regardless of diet. This does not mean diet does not matter for them; it means their threshold for problems is lower.
The interaction between genes and lifestyle is now an active research area. One prospective cohort study found that lifestyle factors like diet and exercise influenced diverticular disease risk independently of genetic susceptibility, meaning that even people at higher genetic risk can reduce their odds by modifying behavior.7PubMed Central. Lifestyle, genetic susceptibility, and risk of diverticular disease: a prospective cohort study
The Gut Microbiome
The role of gut bacteria in diverticulitis is a relatively new area of investigation, and the picture is still emerging. A study comparing the microbiomes of people with asymptomatic diverticulosis (pouches but no inflammation) to healthy controls found that overall microbial diversity was similar between groups. However, certain species differed in abundance: beneficial bacteria like Bifidobacterium pseudocatenulatum and Prevotella copri were enriched in healthy controls, while other species were more abundant in those with diverticulosis.23PubMed Central. Gut microbiome structure and function in asymptomatic diverticulosis Overall, microbiome composition explained less than 2% of the variation in disease status, which suggests the microbiome is a contributing factor rather than a primary driver.
Emerging evidence suggests that chronic low-grade inflammation in the colon can alter the local microbial community over time, creating a feedback loop. This dysbiosis may then affect the neuroendocrine system in the gut wall, leading to heightened sensitivity and alterations in the gut-brain axis.24Exploration of Digestive Diseases. Diverticulitis—new evidence to share with patients In plain terms, the inflammation from diverticulitis changes which bacteria thrive, the altered bacteria may sustain inflammation, and the whole process may rewire how the gut communicates with the brain, helping to explain the chronic pain and bowel irregularity that some patients experience between acute episodes.
Why Geography Changes the Disease
Diverticular disease does not look the same everywhere. In Western countries, diverticula overwhelmingly form in the left colon, particularly the sigmoid segment. In Asian countries, right-sided diverticula are far more common.25PubMed Central. The Burden of Diverticular Disease and Its Complications: West versus East These geographic patterns are so distinct that researchers consider left-sided and right-sided diverticular disease to be largely separate disease processes.26PubMed Central. The Epidemiology and Etiology of Right-Sided Colonic Diverticulosis: A Review
Left-sided disease is strongly linked to the lifestyle and dietary factors described throughout this article: low fiber, high red meat, excess visceral fat, sedentary behavior. Right-sided disease, more common in younger patients in Asia, appears to involve more of a congenital structural predisposition, with thinner colon walls on the right side playing a larger role than diet. As Asian countries have increasingly adopted Western dietary patterns, left-sided disease has become more common there too, while right-sided disease rates have remained stable, which reinforces the environmental component of left-sided diverticulitis.
What Drives Recurrence
If you have had one episode of diverticulitis, your risk of having another is substantially elevated. The strongest predictor of recurrence is simply having had previous episodes: two or more prior bouts more than double the risk of subsequent recurrence.27PubMed. Risk factors for recurrence after acute colonic diverticulitis: a systematic review Having had an abscess during a prior episode increases recurrence risk even further. One study found that abscess history and corticosteroid use were both powerful predictors of complicated recurrence, with corticosteroid medication carrying a particularly high hazard.28PubMed Central. Assessment of risk for recurrent diverticulitis: a proposal of risk score for complicated recurrence Younger patients also appear to recur more often, which may reflect more aggressive disease biology or simply more years of exposure.
Surgery does not eliminate recurrence entirely. Even after resection of the affected colon segment, about 6% of patients in one systematic review experienced recurrence. Risk factors for post-surgical recurrence included having irritable bowel syndrome, the level of the surgical connection (anastomosis), and persistent postoperative pain.29PubMed Central. Surgical resection does not avoid the risk of diverticulitis recurrence-a systematic review of risk factors The fact that IBS status predicted recurrence after surgery is notable, because it suggests that some of the symptoms attributed to diverticular disease may actually be driven by underlying motility or sensitivity disorders that persist even when the diverticula are removed.
Segmental Colitis Associated With Diverticulosis
A less well-known condition called segmental colitis associated with diverticulosis, or SCAD, deserves mention because it can mimic both diverticulitis and inflammatory bowel disease. SCAD involves inflammation of the colon wall between diverticula rather than inside them, typically affecting the sigmoid and descending colon. Patients present with abdominal pain, diarrhea, and sometimes blood in the stool.30PubMed Central. Segmental Colitis Associated With Diverticulosis Under a microscope, the tissue shows features of chronic colitis including crypt distortion, inflammation in the supporting tissue, and occasionally granuloma formation, findings that can look strikingly similar to Crohn’s disease.
SCAD is rare, but it matters for anyone with diverticular disease who develops chronic symptoms that do not fit the usual pattern of acute flares followed by recovery. Distinguishing SCAD from Crohn’s or from recurrent diverticulitis affects treatment decisions: SCAD sometimes resolves on its own or responds to anti-inflammatory medications, while Crohn’s requires a different long-term strategy and diverticulitis may eventually warrant surgery. A colonoscopy with biopsy is typically needed to tell these conditions apart.