Although not proven, the dominant theory is that a low-fiber diet causes diverticulitis. The disease was first noticed in the United States in the early 1900s, around the time processed foods were introduced into the American diet. Consumption of processed foods greatly reduced Americans’ fiber intake.
Diverticular disease is common in developed or industrialized countries—particularly the United States, England, and Australia—where low-fiber diets are consumed. The disease is rare in Asia and Africa, where most people eat high-fiber diets.
Fiber is the part of fruits, vegetables, and grains that the body cannot digest. Some fiber, called soluble fiber, dissolves easily in water. It takes on a soft, jelly-like texture in the intestines. Insoluble fiber passes almost unchanged through the intestines. Both kinds of fiber help prevent constipation by making stools soft and easy to pass.
Constipation—or hard stool—may cause people to strain when passing stool during a bowel movement. Straining may cause increased pressure in the colon, which may cause the colon lining to bulge out through weak spots in the colon wall. These bulges are diverticula.
Lack of exercise also may be associated with a greater risk of forming diverticula, although the reasons for this are not well understood.
Doctors are not certain what causes diverticula to become inflamed. The inflammation may begin when bacteria or stool are caught in the diverticula. An attack of diverticulitis can develop suddenly and without warning.