DiarrhoeaHaving frequent, loose or watery stools can be one of the side-effects of cancer treatment.

But what causes diarrhoea and what can you do about it?

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> Causes of diarrhoea
> What should I do if I have diarrhoea?
> Nutritional tips for dealing with diarrhoea

Diarrhoea (frequent, loose or watery stools) can be a side-effect of cancer treatments such as chemotherapy, radiotherapy, targeted therapies and surgery.

What causes diarrhoea?

Food is not usually the cause, so you don’t usually need to avoid any specific foods or drinks. Diarrhoea can be caused by chemotherapy and also radiotherapy if the small bowel is in the radiation area. Irradiation can cause inflammation of the lining of the small bowel which can also cause diarrhoea.

When the large bowel and rectum is in the irradiation area the rectum can lose its storage capacity. This may make you think you need to go to the toilet but then nothing comes out or you may do small poos (stools). This may seem similar to diarrhoea, but it’s not the same.

Diarrhoea can also be caused by a tumour in the large bowel or rectum or the surgical removal of part of the bowel. It can also be caused by lactose intolerance or by reduced absorption of fat. Diarrhoea can also be caused by viruses, bacteria, and parasites.

Antibiotics and diarrhoea

Diarrhoea can also be caused by antibiotics. Antibiotics kill certain healthy gut bacteria – this helps bacteria that cause diarrhoea in the gut to increase.

Colon cancer and overflow diarrhoea

If you have a tumour in the colon or rectum your gut may be partially blocked. This prevents the thick stool from passing through the narrowed area. The fluid from the stool can still pass. This makes it seem like you have diarrhoea. This is called “overflow diarrhoea”. The stool is watery, and you feel full. If you have overflow diarrhoea you should avoid foods that are high in fibre. The extra fibre will fill your gut even further and aggravate the diarrhoea. You should speak to your doctor or dietitian for advice.

Pancreatic cancer and diarrhoea

The pancreas secretes substances that are important in the digestion of dietary fats. In pancreatic cancer, the secretion of these substances may be disturbed. This means that the absorption of fats by the bowel is reduced, and fatty diarrhoea can develop. This fatty diarrhoea often floats in the toilet or sticks to the sides of the toilet. This diarrhoea smells more and is lighter in colour than ordinary diarrhoea and is also known as steatorrhoea diarrhoea. Do you recognise your stool in this description? Speak to your doctor and ask for advice.

What should I do if I have diarrhoea when going through cancer treatment?

If you have diarrhoea, it’s important to seek advice from your doctor, as there are many causes that require different types of treatment. If you’re prescribed medication to help with diarrhoea, it’s important you take it as directed.

If you continue to have diarrhoea after your treatment has finished – or beyond the time you were told you might experience problems – get further advice from your doctor.

Nutritional tips for dealing with diarrhoea

There are also a number of things you can do yourself if you have diarrhoea.

Make sure you drink at least two litres of fluid each day

You can lose lots of water through diarrhoea, and this puts you at risk of dehydration. Soup, custard, yoghurt, jelly, ice lollies or similar products also count as liquids.

Take extra salt

It’s important to take extra salt each day to make up for the salts lost in the diarrhoea. You can do this by drinking salty fluids such as soup, Marmite, Bovril, stock or using oral rehydration salts (ORS). If you are having IV fluids (a “drip”) extra salt can be administered via the infusion.

Eat small meals or snacks regularly

Take your time when eating and chew your food well.

Eat a varied diet, without strict restrictions

There are no specific foods that stop diarrhoea.

Limit the use of products containing the sweetener sorbitol

Sorbitol is found in some diet/light products and sugar-free chewing gum. It’s better not to use this because sorbitol can cause diarrhoea. Check the ingredients list on the food or drink label to see if it contains it.

If the diarrhoea is cause by antibiotics

It may be helpful to use certain probiotics. The antibiotics kill healthy gut bacteria, which helps the bacteria that cause diarrhoea to multiply. Probiotics contain ‘good’ bacteria which can help to rebalance your gut.

Probiotics are available in the supermarket, health stores, or on the internet in the form of dairy products or capsules or powders. The label will tell you whether the product contains probiotics. You can also buy probiotics from the pharmacy in the form of capsules or powders. It’s best to speak to your dietitian or doctor first to make sure you are taking the right product for you.

If the diarrhoea is caused by inflammation of the mucous membrane of the bowel (mucositis) or if you have a weakened immune system, do not use probiotics. Ask your doctor what caused your diarrhoea and ask for further advice.

Avoid large meals and high-fat meals

Such as foods with a lot of cheese or cream, and fried food, carbonated drinks, hot herbs, and spices such as (chilli) pepper, garlic, and onions. These products can all cause accelerated bowel movements, gas formation or irritation of the intestinal mucosa.

Try to include wholegrain foods

Try to include wholegrain varieties of bread, brown rice and pasta, and softly cooked fruits and vegetables. Fibre acts like a sponge, absorbing water. Without enough fluid, the fibre cannot do its job and you increase the chance of getting constipated. It is therefore important to drink enough fluids, especially water.

Use milk or dairy products in moderation

Set a limit of three servings of milk or dairy products spread throughout the day. Sour milk products such as buttermilk and yoghurt are often better tolerated because part of the lactose (the sugar in the milk) has already been broken down.

Coffee and alcoholic drinks should be consumed in moderation

Choose decaffeinated coffee and tea where possible or have weak coffee, because caffeine has a stimulating effect on the intestinal function, which may lead to diarrhoea.

Foods to avoid

Some people find certain foods can make their diarrhoea worse, so you might want to consider whether these foods affect you. If they do, try avoiding them or reducing the amount you eat:

  • Greasy, fatty and fried foods
  • Caffeine, such as in tea, coffee, cola and chocolate
  • Spicy foods
  • Alcohol
  • Nuts and seeds

Can a low-fibre diet help?

Until recently, people with diarrhoea were advised to reduce the amount of fibre in their diet. However, for many causes of diarrhoea, including chemotherapy and radiotherapy, there is actually no evidence that this will have any benefit.

This is good news as it means that people can often continue to eat a normal, healthy, balanced diet containing adequate amounts of fibre-containing foods, such as vegetables, fruit, pulses (like beans and lentils) and wholegrain foods.

Are there foods that can stop diarrhoea?

No. There are no foods that can stop diarrhoea. People sometimes say bananas or white bread do but this isn’t true.

Note: if you suffer persistent diarrhoea, please consult your doctor. They can prescribe certain medications.

For more advice, get a copy of our Eat Well During Cancer guide

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