Sigmoid diverticulosis develops when small pouches push outward through weak spots in the wall of the sigmoid colon, the S-shaped segment of your large intestine just above the rectum. It affects roughly half of all people over age 60 in Western countries, and the likelihood climbs steadily with each decade of life. The condition results from a combination of structural vulnerabilities, pressure dynamics inside the colon, dietary patterns, genetic predisposition, and age-related tissue changes rather than any single cause.
Why the Sigmoid Colon Is Vulnerable
The sigmoid colon is the narrowest segment of the large intestine, and that matters. When the muscular wall contracts to move stool along, the pressure generated inside a narrow tube is higher than in a wider one. The sigmoid also has to do more mechanical work than the rest of the colon because stool is at its driest and most compact by the time it reaches this final stretch, requiring stronger contractions to push it toward the rectum.
The colon wall itself has built-in weak points. Blood vessels called vasa recta supply the intestinal lining, and each one pierces straight through the muscular layer to reach the inner tissue. These penetration sites create small gaps in the muscle where the wall is thinner. Under sustained or repeated high pressure, the inner lining can be forced outward through these gaps, forming the characteristic pouches. This is why diverticula almost always appear between the bands of longitudinal muscle (called taeniae coli) rather than through them.
How Aging Weakens the Colon Wall
The total amount of collagen in your colon wall stays relatively constant as you age, but the structure of that collagen changes significantly. After about age 40, the cross-linking between collagen fibers increases, making the tissue stiffer and less elastic. Paradoxically, stiffer collagen is also more brittle. Research published in the journal Gut found that in people over 60 with diverticulosis, the acid solubility ratio of collagen (a marker of structural change) was dramatically higher than in unaffected colons of the same age, indicating the protein had undergone significant reorganization.
These changes mean the colon wall loses its ability to stretch and recoil under pressure. Instead of flexing when the sigmoid contracts, the weakened areas give way. The combination of increasing internal pressure and decreasing wall resilience explains why diverticulosis is rare before 40 and nearly ubiquitous in older adults.
The Role of Dietary Fiber
Low fiber intake has been the dominant explanation for sigmoid diverticulosis since the early 1970s, when researchers observed that the condition was common in Western countries but rare in rural Africa, where diets contained far more plant fiber. The theory holds that fiber adds bulk and moisture to stool, allowing it to pass through the colon with less muscular force. Without adequate fiber, the colon has to generate higher pressures to move small, hard stools, and those pressures are concentrated in the sigmoid.
This “low fiber, high pressure” model remains influential, though it is likely one piece of a more complex picture. Not everyone who eats a low-fiber diet develops diverticula, and some high-fiber populations do develop them. Still, fiber intake is the most modifiable risk factor. Current guidelines recommend about 14 grams of fiber per 1,000 calories consumed, which works out to roughly 28 grams per day on a standard 2,000-calorie diet. Most adults in Western countries eat well below that threshold.
Genetic Factors
Your genes account for a surprisingly large share of your risk. Twin studies estimate that 40 to 53 percent of individual susceptibility to diverticular disease comes from heritable factors, putting genetics on roughly equal footing with all environmental and lifestyle factors combined.
Large-scale genetic studies have begun identifying specific genes involved. Some of the most notable include a gene that encodes elastin, a key structural protein in the intestinal wall, and another that regulates the pacemaker cells controlling rhythmic contractions in the gut. Other identified genes relate to immune function and the integrity of the intestinal lining. The discovery of families where young, otherwise healthy members develop severe diverticular disease has further confirmed a strong genetic component, with specific gene variants linked to these early-onset cases.
Visceral Fat and Inflammation
Carrying excess fat around your abdominal organs (visceral fat) does more than add mechanical pressure on the colon. Visceral fat is metabolically active tissue that releases inflammatory signaling molecules. As visceral fat increases, it attracts immune cells called macrophages, which become activated and sustain a low-grade inflammatory state. This chronic inflammation appears to weaken the gut barrier over time.
Research has shown that increasing visceral fat correlates with higher levels of an intestinal inflammation marker called fecal calprotectin, even in people with diverticulosis who haven’t yet developed acute complications. The inflammatory environment may compromise the colon wall’s structural integrity, making it more susceptible to pouch formation. It also helps explain why obesity is consistently linked not just to having diverticula but to developing painful complications from them. When the gut barrier is breached during inflammation, bacteria can migrate into the surrounding fat, potentially triggering or worsening diverticulitis.
Changes in Nerve and Muscle Function
The colon has its own nervous system, called the enteric nervous system, which coordinates the wave-like contractions that move stool forward. This system relies on a balance between nerves that trigger contraction and nerves that trigger relaxation. When that balance shifts, it can lead to disorganized motility: some segments contract too forcefully while others relax too much, creating pockets of high pressure.
In the sigmoid colon specifically, abnormal patterns of segmented contraction can effectively pinch off short sections of the colon, trapping gas or stool and generating localized pressure spikes. Over years, these repeated pressure spikes push tissue outward at the weakest points. Age-related loss of nerve cells in the colon wall may contribute to this dysfunction, though the exact mechanisms are still being mapped.
Medications That Raise Risk
Chronic use of common pain relievers can contribute to diverticular problems. Regular use of NSAIDs (ibuprofen, naproxen, and similar drugs) was associated with a 72 percent increased risk of diverticulitis and a 74 percent increased risk of diverticular bleeding compared to nonuse, in a large study following tens of thousands of men. Regular aspirin use carried a smaller but still significant increase: 25 percent higher risk for diverticulitis and 70 percent higher for bleeding.
These medications damage the colon lining through two pathways. They directly irritate the mucosal surface, and they suppress the production of protective compounds called prostaglandins that help maintain the barrier between the intestinal contents and the colon wall. This increased permeability allows bacteria and other irritants to reach vulnerable tissue. NSAIDs also inhibit blood clotting, which means existing weak spots in blood vessels near diverticula are more likely to bleed. The association was strongest for complicated diverticulitis, where NSAID users had roughly 2.5 times the risk compared to nonusers.
How These Factors Work Together
Sigmoid diverticulosis is not caused by any single factor acting alone. The most accurate picture is a convergence: you inherit a colon wall with a certain structural resilience and a certain motility pattern. Over decades, collagen cross-linking stiffens the tissue. A low-fiber diet forces the sigmoid to work harder. Visceral fat adds a layer of chronic inflammation. Medications may thin the protective lining. The sigmoid, already the narrowest and highest-pressure segment, bears the brunt of all these forces at the points where blood vessels have created natural gaps in the muscle wall.
This explains why the condition is so common in older adults in industrialized countries, where low-fiber diets, sedentary lifestyles, higher body fat, and frequent NSAID use all converge with the inevitable effects of aging on connective tissue. It also explains why some people develop diverticula in their 30s while others reach 80 without them: genetic variation in collagen structure, elastin production, and gut motility creates a wide range of baseline vulnerability.