Diverticular disease is a digestive condition where small pouches form in the wall of the colon and go on to cause symptoms, bleeding, inflammation, or complications. These pouches, called diverticula, are extremely common as people age. When they sit quietly and cause no trouble, the condition is simply called diverticulosis. When they become inflamed or lead to problems, the broader term “diverticular disease” applies, with diverticulitis being its most well-known form.
How Diverticula Form
The wall of your colon has natural weak spots where blood vessels pass through the muscle layer. Over time, pressure inside the colon can push the inner lining outward through these weak points, creating small bulging pockets. Think of it like an inner tube poking through a worn spot in a tire.
This process tends to happen most in the sigmoid colon, the S-shaped section in your lower left abdomen. That part of the colon has the smallest diameter, so it experiences the highest internal pressures during normal digestion. Aging accelerates the process because collagen in the colon wall becomes stiffer and less elastic with time, making the tissue more prone to these small herniations. This is why diverticulosis is far more common in people over 60, though the incidence among adults under 40 has been rising sharply over the past two decades.
Diverticulosis vs. Diverticulitis
Most people who develop diverticula never know they have them. Diverticulosis is often discovered by accident during a colonoscopy or imaging scan done for another reason. It requires no treatment and, in many people, never progresses further.
Diverticulitis occurs when one or more of these pouches becomes inflamed or infected. This is what most people picture when they hear “diverticular disease,” and it can range from a mild episode that resolves on its own to a serious emergency. The distinction matters because the two conditions call for very different responses.
Symptoms of Diverticulitis
The hallmark symptom is abdominal pain, usually in the lower left side, that comes on relatively suddenly and can be severe. The pain may spread to your pelvis or radiate to your back. Other common symptoms include fever, nausea and vomiting, a bloated or tender abdomen, constipation (or less commonly diarrhea), and occasionally rectal bleeding.
There’s a geographic and ethnic variation worth noting. In people of Asian descent, diverticula more commonly develop in the first part of the colon, which sits in the upper right abdomen. Diverticulitis in that location can mimic appendicitis or gallbladder trouble, making it harder to identify without imaging.
Risk Factors
Both genetics and lifestyle play a role. A large study using genetic risk scores alongside lifestyle data found that five modifiable factors independently raise the risk of developing diverticulitis: smoking, excess weight, low physical activity, low fiber intake, and high red or processed meat consumption. The size of each effect is worth knowing:
- Body weight: Being overweight raises the risk by 32%, and obesity raises it by 44%, compared to a BMI under 25.
- Smoking: Former smokers are 17% more likely and current smokers 13% more likely to be diagnosed than people who never smoked.
- Physical activity: Higher activity levels are linked to a 16% lower risk.
- Fiber intake: A higher fiber diet is associated with a 14% lower risk.
- Red meat: Higher red meat consumption is tied to a 9% increased risk.
The encouraging finding from that research was that a healthy lifestyle reduced diverticulitis risk regardless of a person’s genetic susceptibility. In other words, even if you’re genetically predisposed, the lifestyle factors still make a meaningful difference.
How It’s Diagnosed
If you show up with sudden lower-left abdominal pain and fever, your doctor will likely suspect diverticulitis, but confirming it requires imaging. A CT scan of the abdomen (usually with contrast dye) is the standard tool. It’s highly accurate, with a 94% sensitivity and 99% specificity, meaning it catches nearly all true cases while rarely flagging something else as diverticulitis by mistake. The scan also reveals whether the episode is uncomplicated or whether a complication like an abscess has developed.
Complications to Watch For
Most episodes of diverticulitis are uncomplicated, meaning the inflammation resolves without lasting damage. But roughly one in four cases involves a complication. The main ones are:
- Abscess: A walled-off pocket of infection near the inflamed pouch. Small abscesses (under 3 cm) are typically treated with antibiotics alone. Larger ones may need to be drained through the skin with a needle guided by imaging.
- Perforation: A tear in the colon wall that can leak intestinal contents into the abdominal cavity, causing a dangerous infection called peritonitis. This is an emergency.
- Fistula: An abnormal tunnel that forms between the colon and a neighboring organ, most often the bladder. Signs include recurring urinary infections or passing gas during urination.
- Stricture: Repeated inflammation can cause scarring that narrows the colon, potentially leading to bowel obstruction over time.
Treatment for Uncomplicated Cases
Guidelines have shifted in recent years. The American Gastroenterological Association now recommends that antibiotics be used selectively rather than routinely for mild uncomplicated diverticulitis in otherwise healthy people. Many episodes can be managed with a temporary liquid or low-fiber diet, pain relief, and rest at home. The inflammation resolves on its own within a week or so for most people.
Antibiotics are still recommended when there are complicating factors: if you have other significant health conditions, if symptoms aren’t improving or you can’t keep fluids down, or if blood tests and imaging suggest more significant inflammation. For complicated diverticulitis involving an abscess, perforation, or fistula, antibiotic treatment is standard and hospitalization is often necessary.
When Surgery Becomes Necessary
Emergency surgery is required when the colon perforates and causes widespread infection in the abdominal cavity. Surgeons classify the severity of these situations using a four-stage system. The earlier stages involve contained abscesses near the colon or deeper in the pelvis, which can sometimes be managed without open surgery. The later stages involve pus or fecal matter leaking freely into the abdomen, which demand urgent intervention.
Elective surgery, meaning a planned operation, is considered for people who have recurring episodes that significantly affect their quality of life. The most common procedure removes the section of colon where diverticula are concentrated. Current guidelines emphasize that the decision should be individualized rather than based on a set number of prior episodes. Minimally invasive (laparoscopic) approaches are now standard for most of these operations, which typically means shorter hospital stays and faster recovery.
Dietary Management
Once an acute flare-up has resolved, the long-term dietary goal is to gradually increase fiber intake to 25 to 30 grams per day. Fiber softens stool and reduces the pressure inside the colon that contributes to diverticula forming and flaring. Good sources include whole grains, beans, lentils, fruits, and vegetables. If your current intake is low, it helps to increase slowly over a few weeks to avoid bloating and gas.
One outdated piece of advice you may still encounter is to avoid nuts, seeds, and popcorn. There is no evidence that these foods trigger diverticulitis, and most gastroenterologists no longer recommend restricting them.