To better understand the causes of diverticular disease and diverticulitis, it is useful to understand how the large intestine (also known as the colon) works.

The large intestine

The large intestine plays two important roles in digestion. It:

• helps remove nutrients from food 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 (poo) when you go to the toilet

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

Lack of fibre

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

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

The pressure of moving the hard, small pieces of stools through your large intestine 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 diverticular disease are almost non-existent. However, in western countries, where many people do not eat enough fibre, diverticula and diverticular disease are much more common.

Diverticular disease

It is not known why only one in four people with diverticula go on to have the symptoms of diverticular disease.

However, factors which appear to increase your risk of developing diverticular disease 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 lead to developing diverticular disease is unclear.

Diverticulitis

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 gets trapped in one of the pouches. This gives bacteria in the stool the chance to multiply and spread, triggering an infection.

Complications of diverticulitis affect one in five people with the condition. Those most at risk are younger people (under 50 years of age).

Some complications associated with diverticulitis are discussed below.

Abscess

The most common complication of diverticulitis is an abscess inside the large intestine (colon). An abscess is a pus-filled cavity or lump in the tissue. Abscesses are usually treated with a technique known as percutaneous abscess drainage (PAD).

A radiologist (a specialist in the use of imaging equipment, such as computerised tomography (CT) scans) uses an ultrasound or CT scanner to locate the site of the abscess.

A fine needle connected to a small tube is passed through the skin of your abdomen (stomach) and into the abscess. The tube is then used to drain the pus from the abscess. A PAD is performed under a local anaesthetic, so it is not particularly painful.

Depending on the size of the abscess, the procedure may need repeating several times before all the pus has been drained. If the abscess is very small – usually less than 4cm (1.5in) – it may be possible to treat it using antibiotics.

Read more about the treating abscesses.

Fistula

A fistula is another common complication of diverticulitis. Fistulas are abnormal tunnels that connect two parts of the body together, such as your intestine and your abdominal wall or bladder.

If infected tissues come into contact with each other they can stick together. After the tissues have healed, a fistula may form. Fistulas can be potentially serious as they can allow bacteria in your large intestine to travel to other parts of your body, triggering infections, such as an infection of the bladder (cystitis).

Fistulas are usually treated with surgery to remove a small section of the colon that contains the fistula.

Peritonitis

In rare cases, an infected diverticula (pouch in your colon) can split, spreading the infection into the lining of your abdomen. An infection of the lining of the abdomen is known as peritonitis.

Peritonitis can be life-threatening, and requires immediate treatment with antibiotics. Surgery may also be required to repair any damage and drain any pus that has built up.

Read more about the treating peritonitis.

Intestinal obstruction

If the infection has badly scarred your large intestine, it may become partially or totally blocked. A totally blocked large intestine is a medical emergency because the tissue of your large intestine will start to decay and eventually split, leading to peritonitis.

A partially blocked large intestine is not as urgent, but treatment is still needed. If left untreated, it will affect your ability to digest food and cause you considerable pain.

In some cases, the blocked part can be removed during surgery.

However, if the scarring and blockage is more extensive, a temporary or permanent colostomy may be needed.

Diverticular disease can be difficult to diagnose from the symptoms alone because there are other conditions that cause similar symptoms, such as irritable bowel syndrome (IBS).

As a first step, your GP may recommend blood tests to rule out other conditions such as coeliac disease (a condition caused by an abnormal immune response to gluten).

Colonoscopy

To confirm you have diverticula (small bulges in the side of the colon) the inside of your large intestine (colon) will be looked at. This can be done with a colonoscopy.

During a colonoscopy, a thin tube with a camera at the end (a colonoscope) is inserted into your rectum and guided into your colon. Before the procedure begins, you will be given a laxative to clear out your bowels.

A colonoscopy is not usually painful, but it can feel uncomfortable. You may be offered painkilling medication and a sedative beforehand to make you feel more relaxed and help reduce any discomfort.

Barium enema X-ray

Another technique for confirming the presence of diverticula is a barium enema X-ray. Barium is a liquid that shows up on X-rays. It is used to coat the inside surface of organs that do not show up on X-ray, such as the colon.

As with a colonoscopy, you will be given a laxative to clear out your bowels before you have a barium enema X-ray.

During the procedure, a tube is inserted into your rectum. The barium liquid is squirted into the tube and up into your rectum. A series of X-rays are then taken.

For a few days after having a barium enema X-ray, your stools will appear white and discoloured due to the barium passing out of your body. It is nothing to worry about.

Diverticulitis

If you have had a previous history of diverticular disease, your GP will usually be able to diagnose diverticulitis from your symptoms and a physical examination. A blood test may be taken because a high number of white blood cells indicates infection.

Further tests will be needed if you have no previous history of diverticular disease. This is to rule out other possible conditions, such as gallstones or a hernia.

A barium enema X-ray may be used, as well as a computerised tomography (CT) scan. A CT scan takes a series of X-ray scans, which are then reassembled by a computer to build up a more detailed 3-D image of the inside of your body.

A CT scan may also be used if your symptoms are particularly severe. This is to check whether the infection has spread to other parts of your body or a complication, such as an abscess, has occurred.

Diverticular disease and diverticulitis are related digestive conditions that affect the large intestine (colon).

Small bulges develop on the lining of the intestine that become inflamed or infected.

Symptoms of diverticular disease include:

• lower abdominal pain
• feeling bloated

Symptoms of diverticulitis include:

• more severe abdominal pain
• high temperature (fever) of 38ºC (100.4ºF) or above

Read more about the symptoms of diverticular disease and diverticulitis.

Diverticulosis, diverticular disease and diverticulitis

Diverticula

Diverticula is the medical term used to describe the small bulges that stick out of the side of the large intestine (colon).

Diverticula are common and associated with ageing. It is thought the pressure of hard stools (poo) passing through the large intestine that has become weakened with age causes the bulges to form.

Read more about the causes of diverticula.

It is estimated that half of people have diverticula by the time they are 50 years old, and 70% of people have them by the time they are 80 years old.

The majority of people with diverticula will not have any symptoms; this is known as diverticulosis.

Diverticular disease

One in four people who develop diverticula will experience symptoms such as abdominal pain.

Having symptoms associated with diverticula is known as diverticular disease.

Diverticulitis

Diverticulitis describes infection that occurs when bacteria becomes trapped inside one of the bulges, triggering more severe symptoms.

Diverticulitis can lead to complications such as an abscess inside the intestine.

Read more about complications of diverticulitis.

Treating diverticular disease and diverticulitis

A high-fibre diet can often ease symptoms of diverticular disease and paracetamol can be used to relieve pain – other painkillers such as aspirin or ibuprofen are not recommended as they can cause stomach upsets in people with diverticular disease.

Mild diverticulitis can usually be treated at home with antibiotics. More serious cases may need hospital treatment to prevent complications.

Surgery to remove affected section of the intestine is sometimes recommended if there’s a risk of serious complications, although this is rare.

Read more about treating diverticular disease and diverticulitis.

Who is affected

Diverticular disease is one of the most common digestive conditions.

There were around 80,000 hospital admissions due to diverticulitis in England in 2010.

Both sexes are equally affected by diverticular disease and diverticulitis, although the condition is more likely to appear at a younger age (under 50) in men than in women.

Diverticular disease is often described as a ‘western disease’ because the rates are high in western European and North American countries, and low in African and Asian countries. Diet is thought to be the reason for this and the fact that people in western countries tend to eat less fibre.

Eating a high-fibre diet may help prevent diverticular disease, and should improve your symptoms.

Your diet should be balanced and include at least five daily portions of fruit and vegetables, plus whole grains. Adults should aim to eat between 18g (0.6oz) to 30g (1.05oz) of fibre a day, depending on their height and weight. Your GP can provide a more specific target, based on your individual height and weight.

It is recommended you gradually increase your fibre intake over the course of a few weeks. This will help prevent side effects associated with a high-fibre diet, such as bloating and flatulence (wind).

Some specialists may suggest not eating nuts, corn and seeds due to the possibility that they could block the diverticular openings and cause diverticulitis. However, there is limited evidence to support this. 

Also drinking plenty of fluids will help prevent side effects.

Sources of fibre

Good sources of fibre include

• fruit
• vegetables
• nuts
• breakfast cereals
• starchy foods – such as bread, rice and pasta

Once you have reached your fibre target, stick to it for the rest of your life if possible.

Some more detailed information on sources of fibre is provided below.

Fresh fruit

Good sources of fibre in fresh fruit (plus the amount of fibre that is found in typical portions) include:

• avocado pear – a medium-sized avocado pear contains 4.9g of fibre
• pear (with skin) – a medium-sized pear contains 3.7g of fibre
• orange – a medium-sized orange contains 2.7g of fibre
• apple (with skin) – a medium-sized apple contains 2g of fibre
• raspberries – two handfuls of raspberries (80g) contains 2g of fibre
• banana – a medium-sized banana contains 1.7g of fibre
• tomato juice – one small glass of tomato jucie (200ml) contains 1.2g of fibre

Dried fruit

Good sources of fibre in dried fruit (plus the amount of fibre found in typical portions) include:

• apricots – three whole apricots contain 5g of fibre
• prunes – three whole prunes contain 4.6g of fibre

Vegetables

Good sources of fibre in vegetables (plus the amount of fibre found in typical portions) include:

• baked beans (in tomato sauce) – a half can of baked beans (200g) contains 7.4g of fibre
• red kidney beans (boiled) – three tablespoons of red kidney beans contain 5.4g of fibre
• peas (boiled) – three heaped tablespoons of peas contains 3.6g of fibre
• French beans (boiled) – four heaped tablespoons of French beans contains 3.3g of fibre
• Brussel sprouts (boiled) – eight Brussel sprouts contains 2.5g of fibre
• potatoes (old, boiled) – one medium-sized potato contains 2.4g of fibre
• Spring greens (boiled) – four heaped tablespoons of Spring greens contains 2.1g of fibre
• carrots (boiled, sliced) – three heaped tablespoons of carrots contains 2g of fibre

Nuts

Good sources of fibre in nuts (plus the amount of fibre found in typical portions) include:

• almonds – 20 almonds contain 2.4g of fibre
• peanuts (plain) – a tablespoon of peanuts contains 1.6g of fibre
• mixed nuts – a tablespoon of mixed nuts contains 1.5g of fibre
• Brazil nuts – 10 Brazil nuts contain 1.4g of fibre

Breakfast cereals

Good sources of fibre in breakfast cereals (plus the amount of fibre found in typical portions) include:

• All-Bran – a medium-sized bowl of All-Bran contains 9.8g of fibre
• Shredded Wheat – two pieces of Shredded wheat contain 4.3g of fibre
• Bran Flakes – one medium-sized bowl of Bran flakes contains 3.9g of fibre
• Weetabix – two Weetabix contain 3.6g of fibre
• muesli (no added sugar) – one medium-sized bowl of muesli contains 3.4g of fibre
• porridge (milk or water) – one medium-sized bowl of porridge contains 2.3g of fibre

Note – the ‘own brand’ equivalents of the cereals mentioned above should contain similar levels of fibre

Starchy foods

Good sources of fibre in starchy food (plus the amount found in typical portions) include:

• crispbread – four crispbreads contain 4.2g of fibre
• pitta bread (wholemeal) – one piece (75g) contains 3.9g of fibre
• pasta (plain, fresh cooked) – one medium portion of pasta (200g) contains 3.8g of fibre
• wholemeal bread – two slices of wholemeal bread contain 3.5g of fibre
• Naan bread – one piece of naan bread contains 3.2g of fibre
• brown bread – two slices of brown bread contain 2.5g of fibre
• brown rice (boiled) – one medium portion of brown rice (200g) contains 1.6g of fibre

Fibre supplements – usually in the form of sachets of powder you mix with water – are also available from pharmacists and health food shops. A tablespoon of fibre supplement contains around 2.5g of fibre.

The Map of Medicine is used by doctors throughout the NHS to determine the best treatment options for their patients. NHS Choices offers everyone in England exclusive and free access to this cutting-edge internet resource, which lets you see exactly what your doctor sees.

The information in the Map has been approved by the UK’s leading clinical experts, is based on the best available clinical evidence, and is continually updated. To take advantage of this unique resource go to:

Map of Medicine: Diverticular disease

The most common symptom of diverticular disease is intermittent (stop-start) pain in your lower abdomen (stomach), usually in the lower left-hand side.

The pain is often worse when you are eating, or shortly afterwards. Passing stools (poo) and breaking wind (flatulence) may help relieve the pain.

Other symptoms of diverticular disease include:

• a change in your normal bowel habits, such as constipation or diarrhoea, or episodes of constipation that are followed by diarrhoea
• bloating
• bleeding from your rectum (back passage)

Diverticulitis

The main symptom of diverticulitis is a constant and severe pain. The pain usually starts below your belly button, before moving to the lower left-hand side of your abdomen.

In Asian people, the pain may move to the lower right-hand side of your abdomen. This is because Asian people tend to develop diverticula in a different part of their colon. The reason for this is thought to be genetic (certain genes found in Asian people may change the natural course of the condition).

Besides severe stomach pain, other symptoms of diverticulitis include:

• a high temperature (fever) of 38ºC (100.4ºF) or above
• feeling sick
• being sick 
• constipation
• bleeding from your rectum

When to seek medical advice

Contact your GP as soon as possible if you think you have symptoms of diverticulitis. The sooner diverticulitis is treated with antibiotics, the lower the risk of complications developing.

If you have symptoms of diverticular disease and the condition has previously been diagnosed, you do not usually need to contact your GP because the symptoms can be treated at home. Read more about treatment of diverticular disease.

If you have not been diagnosed with the condition, contact your GP so they can rule out other conditions with similar symptoms, such as irritable bowel syndrome (IBS).

Most cases of diverticular disease can be treated at home.

The over-the-counter (OTC) painkiller paracetamol is recommended to help relieve your symptoms.

Painkillers known as non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, are not recommended because they may upset your stomach and increase your risk of internal bleeding.

Eating a high-fibre diet may initially help to control your symptoms. Some people will notice an improvement after a few days, although it can take around a month to fully feel the benefits. Read more advice about using diet to improve the symptoms of diverticular disease.

If you have constipation, you may be given a bulk-forming laxative. These can cause flatulence (wind) and bloating. Drink plenty of fluid to prevent any obstruction in your digestive system.

Heavy or constant rectal bleeding occurs in about one in 20 cases of diverticular disease. This can happen if the blood vessels in your large intestine (colon) are weakened by the diverticula, making them vulnerable to damage. The bleeding is usually painless, but losing too much blood can be potentially serious and may need a blood transfusion.

Signs that you may be experiencing heavy bleeding (aside from the amount of blood) include:

• feeling very dizzy
• mental confusion
• pale clammy skin
• shortness of breath

If you suspect that you (or someone in your care) is experiencing heavy bleeding then seek immediate medical advice. Contact your GP at once. If this is not possible then call NHS Direct on 0845 46 47 or your local out-of-hours service.

Diverticulitis

Treatment at home

Mild diverticulitis can often be treated at home. Your GP will prescribe antibiotics for the infection and you should take paracetamol for the pain. It is important that you finish the complete course of antibiotics, even if you are feeling better.

Some types of antibiotics used to treat diverticulitis can cause side effects in some people, including vomitting and diarrhoea. 

Your GP may recommend you stick to a fluid-only diet for a few days until your symptoms improve. This is because trying to digest solid foods may make your symptoms worse. You can gradually introduce solid foods over a two or three day period.

Treatment at hospital

If you have more severe diverticulitis, you may need to go to hospital. Hospital treatment is usually recommended if:

• your pain cannot be controlled using paracetamol
• you are unable to drink enough fluids to keep yourself hydrated
• you are unable to take antibiotics by mouth 
• your general state of health is poor
• you have a weakened immune system
• your GP suspects complications
• your symptoms fail to improve after two days  treatment at home

If you are admitted to hospital for treatment, you are likely to receive injections of antibiotics and be kept hydrated and nourished using an intravenous drip (a tube directly connected to your vein). Most people start to improve within two to three days.

Surgery

In the past, surgery was recommended as a preventative measure for people who had two episodes of diverticulitis as a precuation to prevent complications.

This is no longer the case as studies have found that in most cases risks of serious complications from surgery (estimated to be around one in a 100) usually outweigh the benefits.

However, there are exceptions to this, such as:

• if you have a history of serious complications arising from diverticulitis
• if you have symptoms of diverticular disease from a young age (it is thought the longer you live with diverticular disease, the greater your chances of having a serious complication)
• if you have a weakened immune system or are more vulnerable to infections

If surgery is being considered discuss both benefits and risks carefully with the doctor in charge of your care.

Colectomy

Surgery for diverticulitis involves removing the affected section of your large intestine. This is known as a colectomy. There are two ways this operation can be performed:

• an open colectomy, where the surgeon makes a large incision (cut) in your abdomen and removes a section of your large intestine
• laparoscopic colectomy – a type of ‘keyhole surgery’ where the surgeon makes a number of small incisions in your abdomen and uses special instruments guided by a camera to remove a section of large intestine

Open colectomies and laparoscopic colectomies are thought equally effective in treating diverticulitis, and have a similar risk of complications. Laparoscopic colectomies have the advantage of having a faster recovery time, and cause less post-operative pain.

Laparoscopic colectomies are a relatively new technique and may only be available at specialist surgical centres. There may also be a longer waiting time for this type of surgery.

Stoma surgery

In some cases, the surgeon may decide your large intestine needs to heal before it can be reattached, or that too much of your large intestine has been removed to make reattachment possible.

In such cases, stoma surgery provides a way of removing waste materials from your body without using all of your large intestine.

Stoma surgery involves the surgeon making a small hole in your abdomen known as a stoma. There are two ways this procedure can be carried out. These are explained below.

• An ileostomy, where a stoma is made in the right-hand side of your abdomen (stomach). Your small intestine is separated from your large intestine and connected to the stoma, and the rest of the large intestine is sealed. You will need to wear a pouch connected to the stoma to collect waste material.
• A colostomy, where a stoma is made in your lower abdomen and a section of your large intestine is removed and connected to the stoma. As with an ileostomy, you will need to wear a pouch to collect waste material.

In most cases the stoma will be temporary and can be removed once your large intestine has recovered from the surgery. This will usually take at least nine weeks.

If a large section of your large intestine is affected by diverticulitis and needs to be removed, you may need a permanent ileostomy or colostomy.

Results of surgery

In general terms, surgery is usually successful, although it does not achieve a complete cure in all cases. Following surgery, an estimated one in 12 people will have a recurrence of symptoms of diverticular disease and diverticulitis.