Diarrhoea causes

What are the causes of diarrhoea?

Nutritional Practitioner, BA (Hons), DN, DNT (Distinction)
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An introduction to the causes of diarrhoea

There are many known causes of diarrhoea and different factors can give rise to acute or chronic (long-term) bouts of loose, watery stools.


Gastroenteritis (infection of the gut) caused by bacteria, viruses, parasites or fungi are the most common causes of acute, or short-term, bouts of diarrhoea. Pathogens can release toxins which disturb the movements of electrolytes in our cells, which in turn affects the movement of water between cells and ultimately into the intestines, which can give rise to diarrhoea.

Acute, infectious diarrhoea can easily cause dehydration and is the leading cause of childhood death in the developing world. There is the risk of the infection spreading between people, especially in the presence of poor standards of hygiene and contaminated water sources.

Bacterial or viral infections can also be spread via contaminated sources of food or water. These can give rise to food poisoning if consumed.

Food poisoning is often not too serious, and some people are able to recover within a few days. However in some cases it can be severe and can include persistent vomiting, acute diarrhoea, dehydration taking hold and fever, in which case you should contact your GP.

Low stomach acid

Low levels of stomach acid, or hypochlorhydria, is a common problem which is often misdiagnosed. It can cause a host of problems for the affected individual.

Our stomach acid supports our immune system in defending against pathogens which have found their way into your stomach. In some cases, food contaminated with bacteria doesn’t look or taste much different so we eat it without realising.

The acidic pH of your stomach acid helps keep bacteria, such as Helicobacter pylori (H. pylori), at bay and stops them over-multiplying. Therefore, if our stomach acid is depleted, we are at risk of suffering from bacterial overgrowth and issues such as peptic ulcers can arise.

Insufficient stomach acid also puts you at risk of improper digestion. Food entering the large intestine having not been digested properly is likely to irritate the gut wall and sporadic contractions and diarrhoea can occur.


Irritable Bowel Disease, or IBS, is almost always characterised by uncoordinated contractions of the gut which means diarrhoea, constipation or both are often experienced. Bacterial overgrowth of the digestive tract is thought to be a contributing factor in many cases of IBS.

Our gut naturally contains thousands of different strains of bacteria; however, if the ‘bad’ strains of bacteria overrun the ‘good’, we are at risk of suffering from symptoms commonly associated with IBS, including: bloating, flatulence, pain, constipation or diarrhoea.

Food intolerance

Certain foods or drinks are known to irritate the gut, making diarrhoea a likely outcome. Some examples include food types commonly associated with food intolerance such as: wheat and gluten, dairy and lactose and specific categories of foods known as FODMAPs.

Other ingredients in foods including alcohol, caffeine or artificial sweeteners can irritate a sensitive gut, especially if consumed in excess, and can cause diarrhoea.

Other medical conditions

Diarrhoea is a common symptom of inflammatory gut disorders.

  • Coeliac disease: Coeliac disease is an autoimmune disease caused by an adverse reaction to gluten. The immune system reacts to gluten as though it is a pathogen, which causes significant structural damage and subsequent inflammation to the lining of the gut.

    Digestive issues emerge as the function of the gut is diminished which includes bloating, flatulence, pain, diarrhoea and constipation and over an extended period of time can result in malabsorption, fatigue and weight loss

  • Inflammatory Bowel Disease: Inflammatory Bowel Disease (IBD) is a term used to describe a group of conditions, which as the name suggests, involve chronic inflammation of the gut. Examples of IBD include Crohn’s disease and ulcerative colitis.

    As in Coeliac disease, in the early stages of IBD, digestive complaints are common and include bloating, pain and diarrhoea, but over time more permanent, irreversible damage to the digestive tract can arise and medication or even surgery may be required.

It must be noted that other serious conditions may also cause diarrhoea such as chronic pancreatitis or bowel cancer. If you experience any warning signs alongside diarrhoea you should always visit your doctor.


Conventional medication can have side-effects and some affect the gut. These generally aren’t so well recognised.

A major one to consider with diarrhoea is antibiotics. Antibiotics fight pathogenic bacteria in your body and are often prescribed by doctors for a range of problems including, gastroenteritis, urinary-tract infections, ear infections and tonsillitis.

However, as well as targeting the bad bacteria in our body, antibiotics can also have a detrimental effect on the friendly bacteria residing in your gut. This isn’t always recognised and people often experience digestive troubles after a course of antibiotics without making the connection.

A useful approach to tackle this problem is to take a probiotic supplement alongside your course of antibiotics in order to support the maintenance of your good gut bacteria.

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Your gut is extremely sensitive... emotionally! It’s full of nerves (just like the brain), so when you’re stressed it can become upset, which can lead to diarrhoea or other digestive problems!

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