Causes and Risk Factors of Diverticulitis

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Diverticulitis is a common digestive disease in which small, abnormal pouches in the digestive tract become inflamed or infected. While scientists believe that a low-fiber diet is a major contributor to the disorder, they aren't entirely sure which mechanisms trigger the formation of the pouches (called diverticula) and why symptoms develop in some people and not in others. Among the key risk factors, age, obesity, and smoking are known to contribute to the rise and/or severity of diverticulitis symptoms.

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Common Causes

Diverticulosis—in which persistent pressure on the colon stresses its muscle, causing weak spots to bulge and create pouches called diverticula—is the precursor to diverticulitis. This usually bears no symptoms and is not problematic.

Diverticulitis comes about when those pouches become inflamed or infected, which is what brings about pain.

The intestinal pouches are able to provide bacteria a haven for overgrowth. When this occurs, the low-level inflammation can allow fecal microorganisms to penetrate the already compromised tissues. This can trigger inflammation of the mesenteric tissues (those the attach the intestines to the abdominal wall), which can lead to the development of an abscess or intestinal perforation.

According to research published in the journal, Therapeutic Advances in Gastroenterology, between 10 percent and 25 percent of diverticulitis flares may be attributed to a bacterial infection. 

An imbalance of the bacteria flora has long been suggested as a likely cause of diverticulitis, most specifically elevated level of Escherichia and Clostridium coccoides bacteria. Most research to date, however, has not supported this hypothesis.

While a low-fiber diet has long been implicated as a primary cause of diverticulitis, the evidence in support of this theory remains largely conflicted and inconsistent. It's undisputed, though, that diet does play a significant role in one's risk of diverticulosis and diverticulitis (more on this below).

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Genetics also appears to play a significant role in diverticular diseases. This is supported in part by research conducted in Sweden, which showed that the risk of diverticulitis is more than tripled if you have a fraternal twin with diverticulitis. If your twin is identical, you would have a seven-fold increase in risk compared to the general population, according to researchers.

All told, around 40 percent of all diverticulitis cases are believed to be influenced by heredity (although the exact genetic mutations for this have yet to be identified).


The hypothesis that low-fiber diets are central to the development of diverticular diseases is not without its share of compelling evidence.

Most scientists agree that the formation of the pouches is largely instigated by persistent pressure within the colon, and the key to that is constipation—a condition inherently linked to a lack of dietary fiber. If this happens, stools become harder to pass and cause abnormal distention of intestinal tissues, especially in the sigmoid colon (the section adjacent the rectum where most diverticula develop).


From a historical standpoint, diverticular diseases were first identified in the United States in the early 1900s. This is around the same time that processed foods were first being introduced into the American diet, shifting our intake from milled flours, which are high in fiber, to refined flour, which is low in fiber.

Today, the increased intake of red meat, hydrogenated fats, and processed foods have created a veritable epidemic of diverticular disease in industrialized countries such as the United States, England, and Australia, where the rate of diverticulosis hovers at around 50 percent.

By contrast, diverticular diseases are rare in Asia and Africa, where people tend to eat less red meat and more fiber-rich vegetables, fruits, and whole grains. As a result, the rate of diverticulosis in these regions is less than 0.5 percent.

In 1971, surgeons Denis Burkitt and Neil Painter proposed the theory that a "low-residual diet" high in sugar and low in fiber was responsible for the rise of diverticulitis in Western hemisphere countries. It was a theory that would end up directing the course of treatment for the next 40 years, with doctors routinely prescribing a high-fiber diet as the primary facet of treatment and prevention.

Today, however, there is increasing doubt and confusion as to exact role dietary fiber plays in diverticulitis.

Conflicting Evidence

In 2012, researchers with the University of North Carolina School of Medicine reported that, among 2,104 patients examined by colonoscopy, high fiber intake and frequent bowel movement actually increased the risk of diverticulosis, challenging the long-held belief that low fiber is the primary trigger for disease development.

On the other hand, the bulk of evidence does suggest that a high-fiber diet can prevent some of the more serious complications of diverticulitis. A 2011 study from the Oxford University, which retrospectively analyzed the health records of more than 15,000 older adults, reported that a high-fiber diet was associated with a 41 percent decrease in the number of hospitalizations and deaths from the diverticular illness.

While the conflicting research does nothing to undermine the benefits of a high-fiber diet, it does suggest that diet is less effective in preventing the onset of diverticular diseases and more effective in avoiding the long-term complications.

Other Risk Factors

Age plays a major role in the formation of diverticula, with more than half of the cases occurring in people over 60. While diverticulosis is uncommon in people under 40, the risk can steadily rise the older you get.

By age 80, between 50 percent and 60 percent of adults will have developed diverticulosis. Of these, as many as one in four will have diverticulitis.

Obesity is also a major risk factor. A 2009 study from the University of Washington School of Medicine, which tracked the health records of more than 47,000 men over a period of 18 years, concluded that obesity—defined as a body mass index (BMI) of over 30—nearly doubled the risk of diverticulitis and tripled the risk of diverticular bleeding compared to men with a BMI under 21.

Smoking is, perhaps not surprisingly, a concern, too. The habit is known to contribute to inflammation that can increase one's risk of a number of health issues, and it can contribute to diverticulitis by promoting inflammation that undermines already compromised tissues, increasing the risk of abscesses, fistula, and intestinal perforation. The risk appears to be greatest in people who smoke over 10 cigarettes per day, according to research from Imperial College London.

Nonsteroidal anti-inflammatory drugs (NSAIDs) is also closely linked to diverticulitis and diverticular bleeding. While aspirin has long been considered the prime suspect, it has since been shown that all NSAIDs have the same potential for harm. They include such popular, over-the-counter brands as Aleve (naproxen) and Advil (ibuprofen).

By contrast, oral corticosteroids and opiate analgesics are more likely to cause perforated diverticulitis, doubling and tripling the risk respectively. The risk is seen to increase with prolonged use.

Frequently Asked Questions

  • What is the difference between diverticulosis and diverticulitis?

    Diverticulosis is a precursor to diverticulitis. It’s caused by persistent pressure on the colon that stresses the muscle and causes weak spots to bulge and form pouches known as diverticula. The diverticula can trap bacteria and become infected, causing diverticulitis. 

  • What are the risk factors for diverticulitis?

    Risk factors for diverticulitis include heredity, being age 60 or older, having a BMI over 30, smoking, and regular use of NSAIDs such as aspirin.  

  • Is constipation a risk factor for diverticulitis?

    Yes. Chronic constipation can put pressure on the intestinal walls causing diverticulosis, which can lead to diverticulitis. 

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Granlund J, Svensson T, Olén O, et al. The genetic influence on diverticular disease--a twin study. Aliment Pharmacol Ther. 2012;35(9):1103-7.

  2. Peery AF, Barrett PR, Park D, et al. A high-fiber diet does not protect against asymptomatic diverticulosis. Gastroenterology. 2012;142(2):266-72.e1. doi:10.1053/j.gastro.2011.10.035

  3. Crowe FL, Appleby PN, Allen NE, Key TJ. Diet and risk of diverticular disease in Oxford cohort of European Prospective Investigation into Cancer and Nutrition (EPIC): prospective study of British vegetarians and non-vegetarians. BMJ. 2011;343:d4131. doi:+10.1136/bmj.d4131

  4. Strate LL, Morris AM. Epidemiology, Pathophysiology, and Treatment of Diverticulitis. Gastroenterology. 2019;156(5):1282-1298.e1. doi:10.1053/j.gastro.2018.12.033

  5. Strate LL, Liu YL, Aldoori WH, Syngal S, Giovannucci EL. Obesity increases the risks of diverticulitis and diverticular bleeding. Gastroenterology. 2009;136(1):115-122.e1. doi:10.1053/j.gastro.2008.09.025

  6. Aune D, Sen A, Leitzmann MF, Tonstad S, Norat T, Vatten LJ. Tobacco smoking and the risk of diverticular disease - a systematic review and meta-analysis of prospective studies. Colorectal Dis. 2017;19(7):621-633. doi:10.1111/codi.13748

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By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.