The gut-brain connection

The steps

1. A two-way line

   The bowel has its own nervous system, and the brain's automatic nerves can speed up or slow digestion. Stress can affect digestion and is one trigger of irritable bowel syndrome.

   Gut-brain axis

   Sources: InformedHealth.org (IQWiG), NCBI Bookshelf, In brief: How does the nervous system work?; healthdirect Australia, Stress; healthdirect Australia, Irritable bowel syndrome (IBS)

2. Microbes join the conversation

   Some studies have found links between gut microbes and the brain, and microbes may play a role in anxiety and depression. Most of this research has been done in rodents, so it is still at an early stage.

   Gut microbiome

   Source: Australian Academy of Science, Gut bacteria: the inside story

3. Serotonin, gut and brain

   Serotonin is one of the brain's chemical messengers. Gut microbes make many brain chemicals, but there is no conclusive evidence that serotonin made by gut microbes reaches the brain.

   Serotonin

   Sources: healthdirect Australia, Antidepressants; Australian Academy of Science, Gut bacteria: the inside story

4. Feeding the conversation

   In the large bowel, bacteria ferment fibre and resistant starch into short-chain fatty acids such as butyrate. A lack of butyrate has been found in people with Crohn's disease.

   Fibre fermentation and short-chain fatty acids

   Source: Australian Academy of Science, Gut bacteria: the inside story

5. When the line gets noisy

   IBS affects around 1 in 5 people. Diet changes with a dietitian, and psychological therapies such as cognitive behavioural therapy and hypnosis, can help.

   Irritable bowel syndrome (IBS)

   Source: healthdirect Australia, Irritable bowel syndrome (IBS)

Quiz