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Professor Lovat
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Young beautiful woman is having stomach ache. Isolated on white.

What is diarrhoea and what causes it?

Diarrhoea is when you pass stools more frequently than normal. The stools are typically looser and more watery. As opposed to constipation, which was discussed last week, diarrhoea occurs because of insufficient water absorption from the bowel. This can happen, for example, if the food you eat passes through your gut too quickly.

Individuals who suffer from irritable bowel syndrome may develop diarrhoea if they consume any of the following foods:

  • Milk: individuals with IBS may not be able to tolerate the proteins found in the milk, due to an allergic reaction, or the special sugar (lactose) found in milk. As well as experiencing diarrhoea, you may also feel bloated or suffer from stomach pain
  • Wheat and grains: Foods that contain these grains may cause discomfort if you suffer from IBS. You may also develop diarrhoea if you consume too much wheat / grains. Interestingly, rice is not always a problem, and in fact, can be beneficial for some individuals as it can prevent too much water being secreted into the gut.
  • Hot drinks: hot drinks can induce contractions within the gut, speeding up the transit of food.
  • Large meals: when you eat, your stomach sends messages to your gut, telling it to contract, in preparation for the arrival of new food. These messages are called the ‘gastro-colic reflex’.
  • Artificial sweeteners: these are found in low-calorie foods to make them taste more appealing. They include aspartame, sorbitol and others. As they are not digested within the gut, they enter the large bowel relatively untouched. In the large bowel they attract water causing any stools present to become more watery.

Other possible triggers of diarrhoea in IBS suffers include:

  • Smoking: smoking can decrease gut-transit time by inducing the contraction of muscles within the large bowel.
  • Drugs: some drugs, such as anti-constipation drugs, can cause diarrhoea if taken in excess. Other drugs, such as anti-biotics, can cause diarrhoea as side effects. Antibiotics can paradoxically increase the number of foreign bacteria within the gut by killing off natural bacteria. The foreign bacteria can produce substances that cause excess contraction of the large bowel

Apart from IBS, diarrhoea may be caused by a wide variety of conditions, some of which are listed here:

  • Infection with viruses, bacteria and parasites
  • Coeliac disease
  • Inflammatory bowel disease, such as Crohn’s disease and ulcerative colitis. A rarer form of inflammation is caused by microscopic or collagenous colitis.
  • Polyps in the large bowel
  • Bowel cancer may present with looser stools and sometimes, with frank diarrhoea
  • Small intestinal bacterial overgrowth
  • Bile salt malabsorption syndrome
  • Certain medicines
  • Anxiety
  • Interacting with people with poor hygiene
  • Drinking contaminated water

Besides a regular need to go to the toilet, diarrhoea may be associated with:

  • Weight loss
  • Loss of appetite
  • Stomach pain

When should I see my doctor?

Normally, diarrhoea will go away within a few days. If, however, if it is very severe, or if any of the following apply to you, you should seek medical care immediately.

  • You have bloody stools
  • You are dehydrated
  • You have recently travelled abroad
  • You have a fever

If you are concerned that you have diarrhoea and it has not gone away after three weeks, then we recommend you book an appointment with one of the consultants at the London Gastroenterology centre.

How is diarrhoea diagnosed?

When you see the doctor, they will normally ask you a series of questions. They will typically ask you about recent travel, the consistency of your stools and other symptoms you may be experiencing.

They may also ask you to provide a stool sample for laboratory testing. Other tests that may be performed include:

  • Blood test
  • Endoscopy to take samples from the small bowel
  • Colonoscopy to examine the large bowel for inflammation and polyps


Although diarrhoea is caused by stools being watery, it is very important to drink plenty. This will not make the diarrhoea worse. You can purchase special oral rehydration solution sachets to replace the essential sugars and ions that you may have lost.

You should continue eating if you experience diarrhoea, although small light meals are recommended.

If your diarrhoea is causing significant discomfort or if it becomes severe, your doctor may advise you take anti-diarrhoeal medication. You may also be advised to take painkillers to deal with any pain-related symptoms, although some pain killers should be avoided as they can mask the symptoms. Always ask your doctor if you are unsure.

Don’t Catch Diarrhoea from Someone Else

To reduce your chance of developing diarrhoea we recommend the following:

  • Wash your hands with soap after toilet use
  • Wash your hands with soap before meals
  • Make sure you cook all meat products properly before consumption
  • Don’t share towels with people who are suffering with diarrhoea
  • Keep your toilet clean!


We hope that you don’t get any bugs. We also hope that you never develop any of the more serious causes of diarrhoea. But if you do, our specialists are here to help you. Please phone our office for an appointment.

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