Diverticular disease develops when small pouches form in the wall of the large intestine and then become inflamed or cause symptoms. The root cause is a combination of pressure buildup inside the colon, structural weakening of the intestinal wall, and several lifestyle and genetic factors that accelerate the process. No single trigger is responsible. Instead, multiple forces work together over time.
How Diverticula Form in the Colon
The wall of your large intestine has natural weak spots where blood vessels pass through the muscle layer. When pressure inside the colon rises too high, the inner lining gets pushed outward through these weak spots, forming small bulging pouches called diverticula. People with diverticula consistently show higher pressure inside the colon compared to people without them.
As you age, the structural proteins that keep the colon wall strong, mainly collagen and elastin, gradually break down and stiffen. This makes the intestinal wall less flexible and more vulnerable to bulging under pressure. That’s why diverticular disease becomes far more common with age, though it’s increasingly being diagnosed in younger adults too. The incidence among people aged 18 to 44 nearly doubled over a seven-year period, rising from 0.15 to 0.25 per 1,000 people. Among those aged 40 to 49, rates of acute diverticulitis jumped 132% between 1980 and 2007.
The Role of Dietary Fiber
Low fiber intake is one of the most well-established risk factors. Fiber adds bulk and water to stool, which moves it through the colon more easily and reduces the pressure your colon has to generate during a bowel movement. Without enough fiber, stool becomes smaller and harder, and the colon must contract with greater force to push it along. That extra force is what drives the pouches outward.
The type of fiber matters. Insoluble fiber, the kind found in whole grains, vegetables, and wheat bran, reduced the risk of diverticular disease by 37% in a large study of health professionals. Cellulose, a specific type of insoluble fiber found in fruits and vegetables, was even more protective, cutting risk by 48%. Most prevention-focused dietary programs aim for at least 25 grams of fiber daily, with some clinical settings pushing toward 40 grams per day for people who have already had an episode.
Genetics and Family History
Your genes play a surprisingly large role. Twin studies estimate that 40 to 53% of your individual susceptibility to diverticular disease comes from heritable factors. That makes genetics roughly as influential as all environmental and lifestyle factors combined.
Researchers have identified dozens of specific gene variants linked to higher risk, including variants in genes involved in connective tissue structure and immune signaling. Some families show patterns of early-onset, severe diverticular disease in otherwise healthy members, which led to the discovery of associated variants in genes called LAMB4 and TNFSF15. If your parents or siblings have had diverticular disease, your own risk is meaningfully higher regardless of your diet or lifestyle.
Gut Bacteria and Inflammation
The balance of bacteria in your gut appears to influence whether diverticula stay quiet or become inflamed. People with symptomatic diverticular disease tend to have less microbial diversity overall, with fewer of the beneficial bacteria that help control inflammation. Specifically, declines in anti-inflammatory bacteria like Clostridium cluster IV, Faecalibacterium, and Ruminococcus have been linked to disease development. At the same time, potentially harmful bacteria such as Fusobacteria tend to increase.
This shift in gut bacteria may help explain why some people have diverticula for decades without symptoms while others develop painful flare-ups. The microbial imbalance can trigger low-grade inflammation in the colon wall, weakening it further and setting the stage for acute episodes.
Body Weight and Physical Activity
Carrying excess weight raises your risk, particularly for diverticulitis, the inflammatory form of the disease. Women with a BMI of 35 or higher had a 42% greater risk of developing diverticulitis compared to women with a BMI under 22.5, even after accounting for other risk factors like diet and exercise. The connection likely involves both increased abdominal pressure and the chronic low-grade inflammation that accompanies obesity.
Physical inactivity compounds the problem. Regular exercise helps maintain healthy bowel motility, reduces colon transit time, and lowers intra-abdominal pressure. Sedentary lifestyles do the opposite, allowing stool to sit longer in the colon and requiring stronger contractions to move it.
Medications That Increase Risk
Certain common pain medications can make diverticular disease worse or trigger complications. Regular use of non-aspirin anti-inflammatory drugs like ibuprofen increased the risk of diverticulitis by 72% and diverticular bleeding by 74% in a large study of men. Aspirin carried a smaller but still significant risk: a 25% increase in diverticulitis and a 70% increase in bleeding among those taking it at least twice per week.
These medications damage the protective lining of the gut, making the thin-walled diverticula more vulnerable to inflammation and rupture. If you already have diverticula, this is worth discussing with your doctor, especially if you take these medications regularly for joint pain or heart health.
Smoking and Diverticular Complications
Smoking doesn’t just increase your risk of developing diverticular disease. It dramatically worsens outcomes when complications arise. In patients with moderate diverticular abscesses, smoking was the single strongest predictor of whether conservative treatment would fail, with smokers more than seven times as likely to need escalated care compared to nonsmokers. Smoking impairs blood flow to the intestinal wall and suppresses local immune responses, both of which make it harder for inflamed diverticula to heal on their own.
Why Cases Are Rising in Younger Adults
Diverticular disease was once considered a condition of aging, rarely seen before age 65. That pattern has shifted substantially. The rise in younger patients tracks closely with population-level changes in diet, body weight, and sedentary behavior over the past few decades. Processed food consumption has increased while fiber intake has dropped. Obesity rates have climbed across all age groups. These environmental shifts, layered on top of genetic predisposition, are pushing the disease into younger populations who previously would not have developed it until much later in life.