Diverticulosis is a condition where small pouches, called diverticula, develop in the lining of the colon. The exact reason why diverticula develop is not known, but they are associated with not eating enough fiber. Fiber makes stools softer and larger, so less pressure is needed by the large intestine to push them out of the body. The pressure of moving hard, small pieces of stools through the large intestine creates weak spots in the outside layer of muscle, allowing the inner layer to squeeze through these weak spots, creating the diverticula.

Diverticulitis occurs when one or more of these pouches become inflamed or infected. Several factors may increase the risk of developing diverticulitis, including aging, obesity, smoking, lack of exercise, a diet high in animal fat and low in fiber, and certain medications.

In summary, diverticulosis is caused by not eating enough fiber, which leads to the development of diverticula, while diverticulitis occurs when these pouches become inflamed or infected due to various risk factors.