Sigmoid diverticulosis is a condition where small, bulging pouches form in the wall of the sigmoid colon, the S-shaped lower section of your large intestine just before the rectum. It is extremely common, affecting roughly half of all people by age 60, and in Western populations about 95% of diverticula appear specifically in the sigmoid colon. Most people never know they have it until the pouches show up on a scan or colonoscopy done for another reason.
Why Pouches Form in the Sigmoid Colon
The sigmoid colon is the narrowest segment of the large intestine, which means it experiences the highest internal pressure when it contracts to move stool along. That pressure is the core reason diverticula cluster here rather than elsewhere in the gut. The pouches develop at naturally weak spots in the colon wall where small blood vessels pass through the muscle layer. Over time, repeated pressure pushes the inner lining of the colon outward through those weak points, creating tiny balloon-like sacs that typically range from 5 to 10 millimeters across.
Age plays a major role. As you get older, the muscle layer of the colon wall gradually weakens and loses elasticity. The nerve cells that coordinate smooth, rhythmic contractions also decline in number, which can lead to uncoordinated squeezing and localized spikes in pressure. These age-related changes explain why diverticulosis is rare before 40 but increasingly common after 60, with peak incidence in people over 70.
What It Feels Like (Usually Nothing)
The defining feature of diverticulosis is that it typically causes no symptoms at all. The pouches sit quietly in the colon wall and don’t interfere with digestion. Many people learn about the condition only after a routine colonoscopy, where the openings of diverticula are plainly visible, or after a CT scan performed for unrelated abdominal complaints.
A smaller subset of people with diverticulosis do experience mild, chronic symptoms: intermittent cramping or tenderness in the lower left abdomen, bloating, and irregular bowel habits that alternate between loose stools and constipation. These symptoms overlap heavily with irritable bowel syndrome, which can make it difficult to pin down whether the diverticula themselves are responsible. When symptoms occur without infection or inflammation, the condition is sometimes called “symptomatic uncomplicated diverticular disease” to distinguish it from the more serious complications.
How It Differs From Diverticulitis
Diverticulosis refers to the mere presence of pouches. Diverticulitis is what happens when one or more of those pouches becomes inflamed or infected. The distinction matters because the two conditions have very different implications. Diverticulosis is a structural finding. Diverticulitis is an acute illness with fever, significant left-sided abdominal pain, and sometimes nausea or changes in bowel habits that require medical treatment.
An estimated 5 to 25% of people with diverticulosis will experience at least one episode of diverticulitis during their lifetime, and up to a third of those who do will develop complications such as abscesses, perforations, or fistulas (abnormal connections between the colon and a neighboring organ). The wide range in that estimate reflects differences in study populations and follow-up periods, but the key takeaway is that the majority of people with diverticulosis never progress to diverticulitis.
Diverticular Bleeding
The other notable complication is bleeding. Because diverticula form at spots where blood vessels penetrate the colon wall, those vessels can become stretched over the dome of a pouch and eventually rupture. This typically shows up as sudden, painless, bright red or maroon-colored blood in the stool. It can be alarming, but most episodes stop on their own without intervention. Diverticular bleeding is one of the leading causes of significant lower gastrointestinal bleeding in older adults.
How Sigmoid Diverticulosis Is Found
CT scanning is considered the standard imaging tool for evaluating diverticular disease. On a CT scan, diverticula appear as small, rounded outpouchings along the colon wall. When inflammation is present, the scan can show thickening of the bowel wall, haziness in the surrounding fat, and fluid collecting in the tissue around the colon. These details help distinguish uncomplicated diverticulosis from active diverticulitis.
Colonoscopy also readily identifies diverticula. During the procedure, the openings of the pouches are visible as dark, round pits in the colon lining. Colonoscopy is better suited for ruling out other conditions like polyps or colorectal cancer but is generally avoided during an acute flare of diverticulitis because of the risk of perforation.
Risk Factors You Can and Can’t Control
Age is the strongest risk factor, and it’s not modifiable. Diverticulosis reaches about 50% prevalence in people aged 60 and older in the United States, Western Europe, and Australia. The condition is far less common in parts of Africa and Asia, a pattern that has long pointed researchers toward diet and lifestyle as contributing factors rather than genetics alone.
Low fiber intake is the most consistently cited dietary risk. A diet low in fiber produces smaller, harder stools that require stronger colonic contractions to move, increasing the internal pressure that drives pouch formation. Current U.S. dietary guidelines recommend 14 grams of fiber per 1,000 calories consumed, which works out to about 28 grams per day on a standard 2,000-calorie diet. Most Americans fall well short of that target.
Obesity raises the risk of complications rather than the formation of diverticula themselves. A large prospective study of men found that those with a BMI of 30 or higher had nearly 1.8 times the risk of developing diverticulitis and over 3 times the risk of diverticular bleeding compared to the leanest group. Waist circumference told a similar story: men in the highest category had roughly double the risk of bleeding. Interestingly, BMI did not significantly increase the risk of developing asymptomatic diverticulosis in that same study, suggesting obesity specifically fuels the inflammatory and vascular complications rather than the pouches themselves.
Physical inactivity, high red meat consumption, and regular use of certain pain relievers (particularly anti-inflammatory medications) have also been associated with higher complication rates in observational research.
Managing Diverticulosis Day to Day
Because most diverticulosis is asymptomatic, management centers on preventing complications rather than treating the pouches. A high-fiber diet is the cornerstone recommendation. Good sources include beans, lentils, whole grains, vegetables, fruits, and nuts. If your current diet is low in fiber, increasing intake gradually over a few weeks helps avoid the gas and bloating that can come with a sudden jump.
The old advice to avoid seeds, nuts, and popcorn has been largely abandoned. Multiple studies have failed to show that these foods increase the risk of diverticulitis or bleeding, and some data suggest nuts and popcorn may actually be protective.
Staying physically active, maintaining a healthy weight, and drinking adequate water all support regular bowel function and reduce the pressure spikes in the colon that contribute to diverticular problems. These are not guarantees against complications, but they meaningfully shift the odds.
When Surgery Becomes an Option
Surgery is not part of the picture for uncomplicated diverticulosis. It enters the conversation only when complications become recurrent or severe. In a review of patients who underwent planned sigmoid colon removal for diverticular disease, the most common reasons were narrowing of the colon from repeated scarring (40%), recurrent flares of diverticulitis with ongoing symptoms (36%), fistulas (14%), recurrent bleeding (7%), and persistent abscesses (3%).
People who take immune-suppressing medications, have chronic kidney disease, or have connective tissue disorders may be considered for earlier surgical intervention after even a single treated episode of diverticulitis, because their risk of severe complications with future flares is significantly higher. For everyone else, the decision is typically based on how much the condition affects quality of life after conservative options have been tried.