Causes of diverticular disease and diverticulitis 

Diverticular disease is caused by small bulges in the large intestine (diverticula) developing and becoming inflamed. If any of the diverticula become infected, this leads to symptoms of diverticulitis.

The exact reason why diverticula develop is not known, but they are associated with not eating enough fibre.

Fibre makes your stools softer and larger, so less pressure is needed by your large intestine to push them out of your body.

The pressure of moving hard, small pieces of stools through your large intestine creates weak spots in the outside layer of muscle. This allows the inner layer (mucosa) to squeeze through these weak spots, creating the diverticula.

There is currently no clinical evidence to fully prove the link between fibre and diverticula. However, diverticular disease and diverticulitis are both much more common in Western countries, where many people do not eat enough fibre.

Diverticular disease

It is not known why only one in four people with diverticula go on to have symptoms of diverticulitis. Diverticular disease may be chronic low-level diverticulitis. The symptoms are very similar to irritable bowel syndrome (IBS) and may overlap.

However, factors that appear to increase your risk of developing diverticular disease include:

Exactly how these lead to developing diverticular disease is unclear.


Diverticulitis is caused by an infection of one or more of the diverticula.

It is thought an infection develops when a hard piece of stool or undigested food gets trapped in one of the pouches. This gives bacteria in the stool the chance to multiply and spread, triggering an infection.

Media last reviewed:

Next review due:

The large intestine

The large intestine plays two important roles in digestion:

  • It helps to remove water and some nutrients from food you eat.
  • It pushes undigested waste products down into your rectum (the end of the large bowel) and out of your anus (back passage), where they are expelled from your body as stools (poo) when you go to the toilet.

The structure of your large intestine is similar to a bicycle tyre. It consists of a flexible inside layer covered by a firmer, tougher layer of muscle. The diverticula are weak as they are made up of the thin, inner layer, which has pushed through the muscle to make a bulge.

The Eatwell Guide (interactive)

If you want to get the balance of your diet right, use the Eatwell Guide. It shows you how much you should eat from each food group

Page last reviewed: 29/09/2014

Next review due: 29/09/2017