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Ask a Dietitian: How Can I Help Manage Diarrhoea?

This series digs into the what, why and how on all your gut-related questions. Today we're looking at diarrhoea. What it is, why it happens and how to help manage it with our expert Gastroenterology Dietitian Dr Sammie Gill.

What is diarrhoea?

Diarrhoea (or ‘the runs’) describes the passing of loose, watery poo and needing to go to the toilet urgently. 

There are different types of diarrhoea - two of the most common are functional diarrhoea (FD) and irritable bowel syndrome with diarrhoea (IBS-D).

While there are similarities between FD and IBS-D, they are separate gut disorders. The main difference between FD and IBS-D is that people with IBS-D will often experience abdominal pain as a main symptom, whereas abdominal pain can be present in FD, though it shouldn’t be the main symptom.

Why does it happen?

FD and IBS-D are chronic forms of diarrhoea and can often develop without a clear cause or trigger.

However, diarrhoea can occur as the result of an underlying health condition, such as inflammatory bowel disease, coeliac disease, small intestinal bacterial overgrowth, and food allergies.

Bile acid diarrhoea (BAD) is an under recognised gut disorder. In fact, it’s thought that over 30% of people who have a diagnosis of IBS-D may have BAD.

Many cases of transient diarrhoea are due to infectious episodes caused by bacteria or viruses, especially when travelling abroad (called traveller’s diarrhoea).

Diarrhoea is also a common side effect of many medications, including antibiotics (called antibiotic-associated diarrhoea).

What can you do to improve it?

First and foremost, it’s important to get the correct diagnosis. This will help optimise management of diarrhoea.

Think about your diet

For IBS-D, trialling the low-FODMAP diet (or a relaxed version) may be recommended. Seek guidance from a healthcare professional trained in the low-FODMAP diet, typically a specialist gastroenterology dietitian.

Watch the sweeteners

Poorly absorbed sugar alcohols (e.g. sorbitol, xylitol, mannitol) that are sugar substitutes and widely used as sweeteners in sweets, gum and drinks can trigger diarrhoea.

Try gut-directed psychological therapies

Psychological therapies have shown effectiveness in IBS including cognitive behavioural therapy, hypnosis, and mindfulness-based therapies.

Be mindful of caffeine

Caffeine increases gut activity by stimulating gut muscle contractions, triggering diarrhoea in some people. Remember, up to 400mg/day (around 5-6 cups of tea or 4 cups of coffee) appears to be safe for most people, though some are more sensitive to caffeine than others.


Some probiotics can be useful in reducing the risk of traveller’s diarrhoea and antibiotic-associated diarrhoea. Choose a probiotic that is evidence-based with research behind the scenario you’re hoping to target.

Read more from our Ask a Dietitian series:

How can I help manage chronic constipation?

How much gas is normal?

NB: There is no one approach to treating diarrhoea and different approaches will work for different people. It’s often a combination of approaches that can help. For tailored advice, please seek advice from a registered dietitian.