Diverticula form when small sections of the colon’s inner lining push outward through weak spots in the muscular wall, creating tiny pouches. This happens at specific points where blood vessels penetrate the colon’s muscle layer to supply its lining, leaving natural gaps in the wall’s structural integrity. By age 40, about 5% of people have these pouches. By age 80, that number climbs to 60–80%.
How the Colon Wall Weakens
The colon wall is made of layers, including a circular muscle coat that gives it strength. Blood vessels called vasa recta pass through this muscle layer to deliver blood to the inner lining, and each vessel creates a small structural gap. These gaps are where diverticula form, almost without exception. The pouches rarely, if ever, push through the thick bands of muscle (taeniae) that run along the colon’s length.
The process starts on the side of the colon closest to its blood supply, where the penetrating vessels are larger and create bigger weak points. Over years of progressive disease, additional rows of pouches can develop on the opposite side, where the vessels are smaller.
Pressure inside the colon is the driving force. The colon naturally contracts in segments to move its contents along, and these contractions temporarily seal off small chambers within the bowel. In a healthy colon, the pressure inside these chambers reaches about 10 mmHg. In people with diverticular disease, pressure can spike to 90 mmHg and last 10 to 20 seconds. That repeated force pushes the inner lining outward through those vessel-created gaps like a balloon inflating through a hole in a tire.
The sigmoid colon, the S-shaped section just before the rectum, is the most common location for diverticula. It has the narrowest diameter of any part of the colon, which means the same muscular contractions generate the highest pressures there.
The Role of Dietary Fiber
Low fiber intake is one of the strongest modifiable risk factors. Fiber adds bulk to stool and speeds its movement through the colon, which means the colon doesn’t have to squeeze as hard to push things along. Less squeezing means lower internal pressure and less force pushing against those weak spots in the wall.
A meta-analysis of prospective studies in the European Journal of Nutrition found a clear, linear relationship: compared to eating just 7.5 grams of fiber per day, consuming 20 grams reduced the risk of diverticular disease by 23%, 30 grams by 41%, and 40 grams by 58%. Not all fiber sources carried equal weight. Fiber from cereals (whole grains, bran) showed a 26% risk reduction per 10-gram increase, and fruit fiber was associated with a 44% reduction. Vegetable fiber, surprisingly, showed no statistically significant benefit in the studies analyzed, though the number of studies was small.
Genetics Account for Nearly Half the Risk
Twin studies estimate that 40–53% of an individual’s susceptibility to diverticular disease comes from inherited factors. That’s a substantial genetic contribution, placing it alongside conditions like type 2 diabetes in terms of heritability.
Researchers have identified several gene variants linked to the disease, and they cluster around a logical theme: the structural scaffolding of the colon wall. One variant affects a gene called LAMB4, which encodes a laminin protein critical to the extracellular matrix, the connective tissue framework that holds cells together. Another involves ELN, the gene for elastin, a protein that gives tissues their ability to stretch and snap back. Elastin has been found to be altered in colon tissue affected by diverticula. People with Williams Syndrome, a genetic condition that includes deletion of the elastin gene, frequently develop diverticular disease. Broader genetic analysis has found enrichment in pathways related to connective tissue development, blood vessel biology, and the extracellular matrix.
Physical Activity and Colon Pressure
Regular vigorous exercise meaningfully reduces the risk of diverticular complications. A large study of men found that those who engaged in roughly 3 hours per week of running or equivalent vigorous activity had a 34% lower risk of diverticulitis and a 39% lower risk of diverticular bleeding compared to men who didn’t exercise vigorously. Notably, non-vigorous activity like walking didn’t show the same benefit.
Exercise appears to help through several mechanisms. It reduces colon transit time, meaning stool spends less time sitting in the bowel. It may lower the internal colon pressure that drives pouch formation, possibly by influencing the autonomic nervous system’s control over bowel contractions. The physical jostling of activities like running may also directly stimulate bowel movement. Less time with stool sitting in the colon also means less bacterial stagnation and potentially less inflammation.
Smoking, Alcohol, and Medications
Both smoking and alcohol consumption increase the risk of developing diverticula, and the relationship is dose-dependent: more cigarettes and more alcohol mean more risk. A large colonoscopy-based study found that age, smoking, and alcohol were all independently significant risk factors, with the prevalence of diverticula increasing in a stepwise fashion alongside consumption levels. Hypertension and atherosclerotic vascular disease were also associated, which makes sense given the vascular nature of the colon’s weak points.
Certain pain medications also raise the stakes, particularly for people who already have diverticula. Regular use of non-aspirin anti-inflammatory drugs like ibuprofen was associated with a 72% increased risk of diverticulitis and a 74% increased risk of diverticular bleeding in a large prospective study. The risk grew with duration of use: after 10 years of regular use, the risk of diverticular bleeding more than doubled. Aspirin carried a smaller but still meaningful increase in risk. These drugs may cause direct topical injury to the colon lining, and because aspirin is mostly absorbed higher in the digestive tract, its effect on the colon is somewhat less pronounced.
Gut Bacteria May Play a Role
The balance of bacteria in the colon appears to shift in people with diverticular disease, though research in this area is still limited by small study sizes and inconsistent methods. People with diverticula tend to have lower levels of certain anti-inflammatory bacterial groups, including Clostridium cluster IV and Lactobacilli, while potentially inflammatory bacteria like Enterobacteriaceae tend to be overrepresented. During acute flare-ups, several studies have found an overgrowth of Bifidobacterium and Akkermansia. Whether these bacterial shifts help cause diverticula or are simply a consequence of the altered colon anatomy isn’t yet clear.
Nuts and Seeds Are Not a Cause
For decades, doctors told patients with diverticula to avoid nuts, seeds, corn, and popcorn, based on the theory that small, hard food particles could lodge in the pouches and trigger inflammation. That advice was never supported by evidence, and it has now been directly contradicted. A large cohort study found that men who ate nuts or popcorn at least twice a week actually had a lower risk of diverticulitis than those who rarely ate them. Popcorn consumption was associated with a 28% reduction in risk. No association was found between corn, strawberries, or blueberries (common sources of small seeds) and any diverticular complications. There is no reason to avoid these foods.