About the bowel

The bowel is the lower part of the digestive system. Your doctor may call the digestive system the gut or gastrointestinal tract (GI tract or GIT for short). The bowel is the bit of the digestive system that goes from the stomach to the back passage (anus). It is a hollow tube.

The digestive system processes all the food we eat and breaks it down into nutrients for the body. It also gets rid of any solid waste matter from the body in the form of faeces (stools).

The bowel is divided into the small bowel (or small intestine) and the large bowel (or colon and rectum). The small bowel is where you digest and absorb the nutrients from the food you eat. The large bowel absorbs water from the digested food and forms stools, or faeces.

Nearly all the problems you are likely to have from cancer are related to the large bowel. It is possible in theory to get an obstruction of the small bowel, but it is rare. There is more information about the bowel and how it works, in the bowel cancer section of CancerHelp UK.

Normal bowel function is affected by

• Muscles and nerves in your bowel, particularly your back passage (rectum and anus)
• What we eat and drink
• How much exercise we get
• Disease and injury
• Age
• Side effects from cancer treatment

Normal functioning of muscles and nerves

The nerves or muscles in your back passage (the rectum and anus) help you have normal bowel movements. So if these nerves and muscles have been damaged by surgery or illness, you may have some difficulty passing stools. The abdominal and intestinal muscles also play a part in moving the stools down into your rectum.

What we eat and drink

You need a certain amount of fluid in your body for your bowel to work properly. If you don’t have enough fluid in your body, you can become dehydrated and you will find it difficult to have a normal bowel movement. So it is important to drink about 2 litres (about 8 tall glasses) of water each day.

What you eat also affects your bowel motions. Eating a diet high in fibre with lots of fresh fruit and vegetables will help keep your stools soft and regular.

Remember - drink plenty of water if you are eating more fibre. Fibre draws water into the bowel so you could become dehydrated if you don’t drink enough.

How much exercise we get

A lack of daily exercise can reduce the muscle tone in your abdomen and bowel (intestines). This slows down the movement of stools through the gut. So taking regular exercise, such as using the stairs rather than the lift or getting off the bus one stop early, will help to keep your bowel working properly.

Disease and injury

Here is information about bowel problems caused by cancer. But many less serious conditions can also change the way your bowel works, and cause similar symptoms. With the right treatment, your doctor can usually control conditions such as inflammatory bowel disease, piles (haemorrhoids) and infections.

Age

The way your bowel works tends to change with age. Bowel problems are more common in the elderly. Understandably elderly people can become less active and may also eat less fibre and not drink enough water. So their abdominal and bowel muscles can become weaker as a result.

Side effects from cancer treatment

Constipation and diarrhoea are common side effects of many drugs. Your doctor should talk to you about the side effects of any new drugs they prescribe for you.

Many drugs used to treat cancer can cause bowel problems. For example, certain types of chemotherapy drugs cause diarrhoea or constipation. And some types of painkillers given to treat cancer pain can cause constipation.

Radiotherapy to the tummy (abdomen) can cause diarrhoea. This usually comes on shortly after the treatment starts and lasts for a week or two after the course of treatment has finished. Your doctor may give you tablets to slow down your bowel and try to prevent diarrhoea.

If you notice any of these side effects, let your doctor or nurse know. They will be able to give you advice about how to treat them.

You might wonder how often you should have a bowel movement. There is no right or wrong answer to this as there is a very wide range of ‘normal’ bowel habits.

It is not essential for you to have one bowel motion a day. It may be normal for some people, but for others going every second day or several times a day is normal.

You can usually think of your bowel habits as ‘normal’ if you

• Have regular bowel movements (not necessarily once a day)
• Don’t have ongoing symptoms of constipation or diarrhoea
• Can have a bowel movement without straining or using laxatives

If you have cancer you should let your doctor know as soon as possible if you have any changes in your bowel habits that may be related to your cancer or treatment.

If you don’t have cancer, and are generally healthy, then a lasting change in your normal bowel habits (diarrhoea or constipation) means a change that lasts for more than 6 weeks.

Remember - bowel problems are very common. Usually, they are not related to cancer, but are caused by certain changes in diet or lifestyle. But there are particular combinations of symptoms that mean your GP should refer you to a specialist straight away.

This section of CancerHelp UK is about cancer symptoms and treatment side effects. If you are worried about bowel cancer symptoms, go to the bowel cancer section for more information.