Diverticular disease and diverticulitis - Causes 

To better understand the causes of diverticular disease and diverticulitis, it is useful to learn about the function of the colon.

The colon

The colon plays two important roles in the process of digestion. The colon:

• helps to remove the nutrients from the food that you eat
• 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 (faeces)

The structure of your colon is similar to that of a tyre. It consists of a flexible inside layer of tissue that is covered by a firmer, tougher layer of muscle.

Lack of fibre

Not eating enough fibre is thought to be a main reason why diverticula (the small pouches that stick out of the side of the colon) develop.

Fibre makes your stools softer and larger so that less pressure is needed by your colon to push them out of your body. Eating low-fibre food produces small, hard stools. These are more difficult for the muscles of your colon to move, and will cause you to strain.

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

There is no clinical evidence to fully prove the link between fibre and diverticula, but the circumstantial evidence is compelling.

For example, in parts of the world where high-fibre diets are common, such as Africa and South Asia, cases of of diverticula and diverticula disease are almost non-existent. However, in western countries, where many people do not eat enough fibre, diverticula and diverticula disease are much more common.

Diverticular disease

It is not known why only 1 in 4 people with diverticula go on to have the symptoms of diverticula disease.

However, a number of risk factors have been identified that appear to increase your risk of developing diverticular disease. These include:

• smoking
• being overweight or obese
• having a history of constipation
• physical inactivity
• use of the non-steroidal anti-inflammatory drugs (NSAIDs) type of painkillers, such as ibuprofen or naproxen

Exactly how these factors lead to the increased risk of developing diverticular disease is unclear.

Diverticulitis

Diverticulitis is caused by an infection of one or more of the diverticula (small pouches that stick out of the side of the large intestine).

It is thought that an infection can develop when a hard piece of stool (faeces) gets trapped in one of the pouches. This gives the bacteria in the stool the chance to multiply and spread, triggering an infection.