Change in bowel habit after treatment

This page has information about how your bowel habit may change after treatment for bowel cancer, including diarrhoea and constipation. 

Regaining bowel control can be a challenge after treatment. For some people, their bowel habits might return to how things were before they had bowel cancer. For others, these changes may be longer lasting. You might experience symptoms such as: 

• loose and runny poo (diarrhoea) 
• leaking poo or not making it to the toilet in time (faecal incontinence) 
• hard, dry poo which is difficult to pass 
• bloating or cramps 
• wind 
• burning (acidic) poo that can irritate the sensitive skin around the bottom 
• an urgent need to empty your bowels (urgency) 
• not being able to empty your bowels completely 
• passing blood or mucus 
• needing to empty your bowels more often

For some people these changes will be mild, for others they can be more serious. These changes can last several weeks and often up to a year. The side effects should improve over time, especially in the first six months, but your bowel habit is unlikely to return to how it was before your diagnosis. 

For some people, these problems can become a long-term condition known as low anterior resection syndrome or LARS. You can find out more about LARS here.

Ask the nurse 

Our nurses are here to help. They can provide you with information, and signpost you to further support. If you have any questions or concerns about bowel cancer, email nurse@bowelcanceruk.org.uk. 

Diarrhoea 

Diarrhoea is loose, runny poo that you pass three or more times a day, or more often than what’s normal for you.  

Bowel cancer treatments, such as surgery, radiotherapy and chemotherapy can cause diarrhoea. Other possible causes include your diet, infections, and medicines like antibiotics. 

When you have diarrhoea, you need to drink enough liquid to avoid getting dehydrated. Take regular small sips and aim for at least six to eight glasses of liquid a day. Avoid sugary or fizzy drinks and drinks that contain caffeine, such as tea and coffee, as these can irritate the bowel and make diarrhoea worse. 

As well as losing water, you will be losing salts and other important nutrients. To replace these, try eating fresh or tinned soups and broths. You could also have Marmite on toast or plain crackers. 

Light, bland and easily digested foods can help with diarrhoea after bowel cancer treatment. Try cutting back on high-fibre foods, such as wholemeal bread, bran-based cereals, and brown rice, especially in the first few weeks and months after surgery and radiotherapy. 

Try to eat small amounts regularly throughout the day and eat slowly to avoid bloating and wind. Tell your healthcare team if you’re having trouble eating or if eating plain food doesn’t improve your symptoms. If you’re not able to get enough nutrients from your food, your healthcare team may refer you to a dietitian. 

It may take you a while to find out which foods make your symptoms better or worse. You may find that your body reacts differently to foods that you could eat in the past. It’s always worth trying foods again to see how you react to them. 

Food and drink to try: 

• water  
• bananas  
• white rice  
• oats  

• pasta  
• noodles  
• white bread or toast  
• crackers  
• low-fibre cereals, such as puffed rice or cornflakes  
• skinned chicken  
• white fish  
• hard boiled eggs 

Food and drink to avoid: 

• drinks containing caffeine  
• alcohol  
• milk and other dairy products  
• fatty foods  
• raw vegetables and fruit  
• beans  
• spicy food  
• high-fibre cereals, such as bran and muesli  
• an artificial sweetener called sorbitol, found in sugar-free sweets and drinks 

If you feel too sick to eat, or if you become very dehydrated, your GP may suggest you use oral rehydration salts. These contain a balance of salts and sugars to help your body re-absorb them quickly. You can buy them from pharmacies and supermarkets. 

Diarrhoea medicines 

Tell your doctor about any medicines and nutritional supplements you’re already taking. They may suggest you stop taking medicines that could be making your diarrhoea worse.  

Always speak to your doctor before taking any medicines for diarrhoea. They'll need to find out what’s causing your symptoms before deciding on the best treatment for you.  

Your doctor may offer you medicines that slow down the movement of your gut (anti-diarrhoea medicines). Examples include loperamide (brand names include Imodium or Dioraleze) or codeine phosphate. They will give you information on how and when to take these medicines.  

If your bowel cancer treatment is likely to cause diarrhoea, your doctor may give you anti-diarrhoea medicine to keep at home in case you need it. If you’re having chemotherapy or chemoradiation, your doctor may give you a medicine called octreotide to treat diarrhoea caused by your cancer treatment. 

Contact your healthcare team if you have any questions about how to take your medicines. They can tell you about products and local services that can help you cope with diarrhoea. 

Probiotics are live bacteria and yeasts that are thought to improve the balance of bacteria in the gut. You can find them in some food products, such as yoghurts, or in food supplements. Some people find they help with diarrhoea but there isn’t enough evidence for health professionals to recommend taking them. 

You should not take probiotics during chemotherapy or if you have low levels of white blood cells because they can increase the risk of infection.  

Always speak to your healthcare team before taking probiotics. 

Constipation 

Constipation is when your poo is hard, dry, and difficult to pass. You may find it painful when you go to the toilet, or you may feel like your bowel isn’t completely empty. If you’re going to the toilet less than three times a week, you’re likely to have constipation. Speak to your GP or healthcare team if you think you have constipation. 

Some people may have symptoms of diarrhoea when they have constipation. This may seem confusing and you may wonder why your doctor is treating your diarrhoea with laxatives. If your poo is blocking your bowel, runny poo can leak through and can look like diarrhoea. Your doctor will work with you to find out what is causing your diarrhoea so you can get the right treatment. 

Get medical advice straight away if you haven’t had a poo for more than a few days and you have pain, feel sick or have been sick (vomited). If you have an ileostomy, contact your stoma care specialist nurse or visit the hospital emergency department if you haven’t passed poo or wind for more than six hours. 

What causes constipation? 

Many things can cause constipation, including:  

• bowel surgery  
• medicines, such as opioid painkillers  
• other illnesses, such as diabetes, thyroid problems or depression  
• not eating enough fibre  
• not drinking enough fluids  
• lack of movement and physical activity 

What should I eat and drink? 

Always speak to your GP or healthcare team before making big changes to your diet. If you’ve had constipation for a long time, you may need medical treatment before you change your diet. 

• Eat at least three meals each day. Try not to skip meals  
• Drink six to eight glasses of fluids, such as water, a day  
• If you’re able to eat fibre without it causing symptoms, add more to your diet, especially wholegrains, vegetables and fruit. Do this gradually and in small portions to avoid wind and bloating

When you’re recovering from treatment, high-fibre foods should be well-cooked and chewed well. This makes them easier to digest. If you’re adding more fibre to your diet, make sure you’re drinking more fluids to avoid getting dehydrated. Be careful not to overdo it. Eating too much fibre can make constipation worse. It can take a few weeks for you to see any change in your bowel habit.  

Foods that may help 

• wholegrain bread, rice, pasta and breakfast cereals  
• porridge oats  
• fresh, tinned or dried fruit that is high in a natural laxative called sorbitol. For example, prunes, raisins, plums, grapes, peaches, raspberries, strawberries, apricots, apples or pears  
• fruit juices high in sorbitol, such as prune juice  
• vegetables  
• peas, beans and lentils 
• ground flaxseeds/golden linseeds

Other things to try: 

• regular physical activity  
• avoiding sitting down for long periods of time  
• making sure you have enough time and somewhere private to go to the toilet, if possible  
• sitting in a squatting position on the toilet, with your knees bent and your feet on a stool. This can help you use the right muscles to empty your bowel  
• not putting off going to the toilet  
• firmly massaging your stomach area in a clockwise movement can help get your bowel moving and can ease bloating and wind

More support and information 

Speak to your healthcare team about any bowel problems you’re having or if your symptoms aren’t getting better. Your specialist nurse can give you information on ways to improve bowel frequency and control. 

Further investigation  

You may need further tests to find the cause of your bowel problems. The tests you have will depend on your symptoms. Below are some examples of tests you might have:  

• blood tests  
• physical examination  
• colonoscopy or flexible sigmoidoscopy – a test that uses a small thin tube with a camera on the end to look inside the body  
• poo samples  
• nuclear medicine scan – a dye is injected into a vein to see if there are damaged or inflamed areas in your bowel. You lie on a bed that slides into a scanner. This is also known as a radionuclide scan

Referral to a specialist  

If the first treatments you try don’t help resolve your bowel problems, your team may decide to refer you to another specialist. This could be a doctor who specialises in treatments for the digestive system (gastroenterologist), a dietitian, a specialist teams that deal with bowel and bladder problems (continence service), or a physiotherapist. 

Find out more about managing bowel function in our booklet Regaining bowel control. 

Our information booklet, Eating well has information on diet, including coping with bowel problems, eating and drinking with a stoma and losing and gaining weight.  

Visit our online communities to talk about your experiences, share knowledge and get support from other people. 

Bladder and Bowel UK have more information and support for people living with conditions which affect their bladder or bowel.  

Page reviewed January 2025