Diverticulitis of the colon is an inflammation or infection of small pouches (called diverticula) that form in the wall of the large intestine. These pouches themselves are common and usually harmless, present in roughly 10% of people by age 40 and more than half of those over 60. But when one or more of them becomes inflamed, the resulting condition, diverticulitis, causes significant pain and can lead to serious complications if left untreated.
How Diverticula Form and Why They Get Inflamed
The colon wall has naturally weak spots where blood vessels pass through the muscle layer. Over time, age-related changes in the tissue combined with increased pressure inside the colon cause the inner lining to bulge outward through those weak points, forming small sacs. Having these pouches is called diverticulosis, and most people who have them never know it.
Diverticulitis happens when something triggers inflammation in one or more of those pouches. There are two leading explanations for what sets it off. In larger pouches, a small piece of hardened stool can become trapped inside the sac, scraping the lining and creating irritation that leads to infection. In smaller pouches, where stool trapping is unlikely, the inflammation may instead result from restricted blood flow. The neck of the pouch can compress surrounding blood vessels during repeated muscle contractions in the colon, starving the tissue of oxygen and triggering an inflammatory response.
What Diverticulitis Feels Like
The hallmark symptom is pain in the lower left side of the abdomen. This is where the sigmoid colon sits, and it’s the most common location for diverticula to develop. The pain can arrive suddenly and intensely, or it can start mild and build over several hours to days. It often worsens when the area is touched or pressed.
Beyond the pain, you may notice fever, nausea, and a change in bowel habits, either sudden diarrhea or constipation. Some people experience bloating or a general sense that something is wrong in the gut. The intensity of symptoms typically reflects the severity of the inflammation. Mild cases may feel like a persistent cramp, while complicated cases can produce high fever and sharp, unrelenting pain.
Who Gets It and Why Rates Are Rising
Diverticulitis has traditionally been considered a disease of older adults, but that picture is changing. Hospital admissions for acute diverticulitis are climbing, particularly among people younger than 60. A recent study in Greece found that 68% of diverticulitis cases occurred in patients under 65, and the total number of cases more than tripled between 2022 and 2024. The trend is closely linked to rising rates of obesity and increasingly sedentary, low-fiber lifestyles in Western countries.
Of everyone who has diverticula, about 7% will eventually develop diverticulitis. Several factors raise that risk:
- Low-fiber diet: Populations that eat more fiber and vegetables, such as those in parts of Asia and Africa, have dramatically lower rates of diverticular disease compared to the U.S., U.K., and Australia.
- High red meat intake: Diets heavy in red meat are associated with increased risk of both diverticula formation and subsequent inflammation.
- Obesity: Excess body weight is a consistent risk factor, especially among younger adults now being diagnosed more frequently.
- Regular use of anti-inflammatory painkillers: Common over-the-counter pain relievers like ibuprofen and naproxen are linked to higher risk.
- Physical inactivity: A sedentary lifestyle contributes independently of diet and weight.
- Genetics: Some people appear to have inherited vulnerabilities in the connective tissue of the colon wall.
How It’s Diagnosed
A CT scan of the abdomen and pelvis is the gold standard for diagnosing diverticulitis. It’s highly accurate, widely available, and can reveal not just the inflamed pouch itself but also whether complications like abscesses or perforations have developed. The American College of Radiology recommends it as the preferred test for anyone presenting with lower left abdominal pain, with one exception: for women of childbearing age, ultrasound is typically the first step to rule out gynecological causes before proceeding to CT.
Blood tests are usually drawn alongside imaging to check for elevated white blood cell counts and other markers of infection, which help gauge severity.
Uncomplicated vs. Complicated Cases
Most diverticulitis is uncomplicated, meaning the inflammation hasn’t caused structural damage beyond the pouch itself. These cases are managed at home with rest, dietary changes, and close self-monitoring. A significant shift in treatment guidelines over the past several years has moved away from automatically prescribing antibiotics for uncomplicated cases. Current European and UK guidelines recommend that if you’re otherwise healthy, not immunocompromised, and don’t have signs of systemic illness, antibiotics provide no meaningful benefit in recovery time or complication rates.
Antibiotics are reserved for people who are visibly unwell with high fever, have weakened immune systems, or show signs of complicated disease. Complicated diverticulitis accounts for 20% to 30% of all cases and includes a spectrum of problems: pus-filled pockets (abscesses) forming near the inflamed pouch, abnormal connections (fistulas) developing between the colon and nearby organs like the bladder, bowel obstruction, or in the most dangerous scenario, a tear in the colon wall that spills intestinal contents into the abdominal cavity. That last complication, peritonitis, is a surgical emergency. About 1% to 2% of diverticulitis patients require hospitalization, and roughly 0.5% need surgery.
What to Eat During and After a Flare
During an active flare, the goal is to give your colon as little work as possible. Most providers recommend starting with clear liquids for a day or two: broth, clear juices like apple or cranberry, plain water, tea or coffee without milk, and gelatin. Sports drinks and ginger ale are also fine at this stage.
After a day or two on clear liquids, you transition to a low-fiber diet as symptoms improve, then gradually increase fiber intake over several days to weeks. Jumping straight to high-fiber foods too quickly can cause bloating and constipation, so the ramp-up matters. The long-term target is 25 to 35 grams of fiber per day, which you can reach through whole grains, fruits, vegetables, beans, lentils, and nuts.
One outdated piece of advice still circulates widely: the idea that you should avoid nuts, seeds, and popcorn to prevent flares. There is no evidence that these foods cause diverticulitis. The theory was that small particles could lodge inside a pouch and trigger inflammation, but studies have never confirmed this, and major medical centers no longer recommend avoiding them.
Reducing Your Risk of Recurrence
If you’ve had one episode of diverticulitis, the most effective thing you can do is build a consistently high-fiber diet. The current 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 this. Minimally processed plant foods are the best sources: think lentils, black beans, oats, berries, broccoli, and whole wheat bread rather than fiber supplements, though supplements can help fill gaps.
Regular physical activity reduces risk independently of weight loss, though maintaining a healthy weight provides additional protection. Cutting back on red meat and avoiding routine use of anti-inflammatory painkillers, when possible, rounds out the prevention strategy. None of these changes guarantee you won’t have another episode, but together they substantially lower the odds.