Diverticular disease describes various conditions that cause tiny sacs, or diverticula, to form in the wall of your large intestine (colon), most commonly in the part of the large intestine closest to your rectum. The sacs form from pressure on the colon wall, forcing it to bulge and develop the sacs. While not clearly understood, your risk for developing diverticular disease increases if you follow a diet that’s high in red meat and low in fiber. The condition also becomes more common as you age.