The main cause of diverticulosis is increased pressure inside the colon, typically driven by a low-fiber diet that makes stool harder and slower to pass. This elevated pressure forces the inner lining of the colon to bulge outward through weak spots in the muscular wall, forming small pouches called diverticula. The condition affects roughly 50% of people over 60 and up to 65% of those over 85, making it one of the most common gastrointestinal findings in older adults.
How Diverticula Form in the Colon Wall
The colon wall has natural weak points where small blood vessels penetrate through the muscle layer. When pressure inside the colon rises, the inner lining herniates through these weak spots, creating small outpouchings covered only by a thin outer layer. These are “false” diverticula because they don’t involve the full thickness of the intestinal wall.
The sigmoid colon, the S-shaped section just before the rectum, is the most common site for diverticula. It has the smallest diameter of any colon segment, which means it generates the highest internal pressures according to basic physics (the same force applied to a smaller area produces more pressure). Abnormal motility patterns, including intestinal spasms, can further segment the colon into isolated chambers where pressure spikes even higher.
Why Low Fiber Intake Matters So Much
A large meta-analysis of five prospective studies covering more than 865,000 participants found a strong, dose-dependent relationship between fiber intake and diverticular disease risk. Compared to people eating only 7.5 grams of fiber per day, those consuming 30 grams daily had a 41% lower risk. At 40 grams per day, the risk dropped by 58%. The relationship was linear: every additional 10 grams of daily fiber reduced risk by about 26%.
Fiber works by adding bulk and water to stool, which increases the diameter of the colon’s contents and reduces the pressure needed to move things along. Without enough fiber, stool becomes compact, transit slows, and the colon has to squeeze harder. Over years and decades, that repeated strain pushes the lining through vulnerable points in the muscle wall. Animal studies confirm the mechanism: low-fiber diets substantially increase the rate of diverticula formation.
Current dietary guidelines recommend 14 grams of fiber per 1,000 calories consumed, which works out to about 28 grams per day on a 2,000-calorie diet. Most people in Western countries fall well short of that target.
The Geographic Pattern Tells the Story
Diverticulosis tracks closely with industrialized diets. The United Kingdom has the highest documented prevalence at 47% among people over 50, followed by the United States at 41.7%. Countries with traditionally plant-heavy diets have far lower rates: South Korea sits at 12.1%, Mexico at 6.65%, Kenya at 5.3%, India at 4.4%, and China at just under 2%.
Notably, countries that have shifted toward Western eating patterns are seeing their numbers climb. Japan (20.3%) and Thailand (28.5%) now fall in the moderate range, likely reflecting decades of dietary change. A diet high in red meat and low in fiber has been associated with increased risk not only for diverticular disease but also for colorectal cancer and other colon conditions.
Aging and Connective Tissue Changes
While diet creates the pressure, aging weakens the wall. The colon’s structural integrity depends heavily on the balance between two types of collagen. Type I collagen provides rigidity, while type III collagen adds flexibility. As people age, the ratio between these two shifts, with more type III collagen being deposited. This makes the colon wall more pliable and more susceptible to bulging under pressure. The combination of decades of elevated intraluminal pressure and progressively weakening tissue explains why prevalence jumps from about 5% in people under 40 to 65% by age 85.
People with connective tissue disorders like Marfan syndrome or Ehlers-Danlos syndrome develop diverticulosis at higher rates and often at younger ages, because their collagen synthesis is fundamentally altered. These cases offer a clear window into how structural weakness in the colon wall contributes to diverticula formation independent of diet.
Genetics Play a Larger Role Than Expected
Twin studies estimate the heritability of diverticular disease at 40% to 53%, meaning genetics account for roughly half the variation in who develops the condition. Large-scale genetic studies using data from populations in Iceland, Denmark, and the UK have identified at least 48 distinct genetic locations associated with diverticular disease, with 35 of those now confirmed through replication. Many of the implicated genes are involved in connective tissue structure and intestinal wall integrity, which aligns with the mechanical understanding of how diverticula form.
Obesity and Physical Inactivity
Carrying extra weight increases your risk. Women with a BMI of 25 to 30 had a 29% higher risk of diverticular disease requiring hospitalization compared to women at a normal weight. At a BMI of 30 or above, the risk increased by 33%. Physical inactivity compounds the problem: women who exercised 30 minutes or less per day had a 42% higher risk than those who were more active. Exercise is thought to help by improving colon motility and reducing transit time, which lowers the pressure buildup that drives diverticula formation.
Gut Bacteria Differences
People with diverticulosis show subtle but measurable shifts in their gut bacteria. Those with the condition tend to have higher levels of certain bacterial species while having lower levels of bacteria linked to healthy, high-fiber diets and improved glucose metabolism. It’s not yet clear whether these microbial shifts help cause diverticulosis or are simply a consequence of the structural changes in the colon. But the pattern is consistent with the broader picture: a gut environment shaped by low fiber and Western dietary habits looks different at the microbial level.
Pain Relievers Can Worsen Complications
Diverticulosis itself is usually silent, but common pain medications can trigger its two main complications: diverticulitis (infection of a pouch) and diverticular bleeding. A 22-year study of more than 47,000 men found that regular use of anti-inflammatory pain relievers like ibuprofen increased the risk of diverticulitis by 72% and diverticular bleeding by 74%. Regular aspirin use raised diverticulitis risk by 25% and bleeding risk by 70%. At moderate doses and frequencies, aspirin was associated with more than triple the risk of bleeding. If you already have diverticulosis, the choice of pain reliever is worth discussing with your doctor, particularly if you rely on these medications frequently.