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About the bowel

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This page tells you about the bowel and how factors such as diet and medicines can affect your bowel movements. You can find information about


Where the bowel is

The bowel is the lower part of the digestive system. The digestive system is also called the gut or gastrointestinal tract (or the GI tract or GIT for short). The bowel is the part 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 poo (also called faeces or 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 poo (stools).


Nearly all the problems you are likely to have from cancer are related to the large bowel. It is possible in theory to get a blockage (obstruction) of the small bowel, but it is very rare. We have detailed information about the bowel and how it works.


Factors that affect how the bowel works

Normal bowel function is affected by

Normal functioning of muscles and nerves

The nerves or muscles in your back passage (the rectum and anus) help you to have normal bowel movements. So if these nerves and muscles are 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 get 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 to drink plenty of water if you are eating more fibre. Fibre draws water into the bowel so you could get 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, helps to keep your bowel working properly.

Other bowel conditions

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


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 or nurse 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 or biological therapy drugs and some types of painkillers cause diarrhoea or constipation. 

Radiotherapy to the pelvic area or to the back passage (rectum) can cause diarrhoea. This usually comes on shortly after the treatment starts and lasts for a few weeks after the course of treatment has finished. Your doctor or nurse may give you tablets to slow down your bowel and try to prevent diarrhoea. There is a trial looking at eating more fibre during pelvic radiotherapy. Doctors want to find out if eating more fibre can help to control diarrhoea caused by pelvic radiotherapy. The trial has closed and we are waiting for the results. 

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.


What a normal bowel habit is

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 bowel habits that are considered normal.

It is not essential for you to have one bowel motion a day. It may be normal for some people, but for other people 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, let your doctor or nurse know as soon as possible if you have any bowel habit changes that may be related to your cancer or treatment.

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

Remember that 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 could be a sign of a serious problem and mean your GP should refer you to a specialist straight away.

This section of our website is about coping with cancer symptoms and treatment side effects. If you are worried that symptoms you have could be caused by bowel cancer, go to the bowel cancer symptoms page.


Talking about bowel problems

Many people find it embarrassing to talk about their bowels and bowel problems. Doctors or nurses may ask you to describe your bowel habits and what your poo (stool) looks like.

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To help health professionals and patients there is a scale of different types of stool called the Bristol stool chart. It has 7 different levels shown in the image below:

Bristol stool chart

If you feel embarrassed about describing your stool you can use the Bristol scale to tell your doctor or nurse what it is like. For example you could say "It is usually type 4 but for the last few days has been type 6".

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Updated: 1 July 2014