Diverticulosis is when small pouches in your colon (large intestine) form and bulge outward through weak spots in the outer colon wall. Each pouch is called a diverticulum, plural pouches are called diverticuli. About 60 percent of Americans over the age of 60 have diverticulosis. When the pouches become infected or inflamed, the condition is called diverticulitis. Diverticulitis happens in only 10 to 25 percent of people with diverticulosis.
The reason pouches form in the colon is not completely understood, however a low-fiber diet may be a main source. If a diet is low in fiber, the colon must force, with more pressure than usual, to move stool through the entire colon. This increase in pressure might cause weak spots in the colon to bulge out and form pouches.
Diverticulitis occurs when diverticulum become inflamed or infected. If a diverticula becomes obstructed, with bacteria, stool, or undigested food caught inside the pouch, bacteria in the pouch may multiply and cause it to swell and become very painful. Swollen diverticuli break and form abscesses, which add to the pain.
Most people with diverticulosis never have any discomfort or symptoms. However, some may have mild cramps, bloating and constipation. If diverticulosis is far advanced and severe, the lower colon may become very fixed or narrowed causing thin stools and constipation. The most common symptom of diverticulitis is abdominal pain with tenderness around the left side of the lower abdomen. If an infection is the cause, fever, nausea, vomiting, chills, cramping and constipation may develop.