Key message: Research shows a link between gut bacteria and mental health.

Action point: Start adding fermented foods such as kombucha, pot-set yoghurt, kim chi, sauerkraut and kefir to your diet on a regular basis for a hit of gut friendly probiotics.

Happy Woman 1While most people think of the brain when considering moods, new research shows that our gut health may, in fact, have a large part to play in our happiness.

Your second brain

Sometimes referred to as the ‘second brain’, hidden in the walls of the digestive system, this ‘brain in your gut’ is revolutionising medicine’s understanding of the links between digestion, mood, health and even the way you think.

Our lower gastrointestinal tract is home to almost 100 trillion microorganisms, most of which are bacteria. They are mostly ‘good’ bacteria that help us digest food and release the energy and nutrients we need. They also crowd out bacteria that can trigger disease.

Recently, researchers have been investigating just how much power these tiny microbes wield over our mental health. They have found when things go pear shaped in our guts, they can also go pear shaped in our brains.

The role of serotonin

The chemical serotonin is largely responsible for maintaining mood balance with a deficiency of serotonin leading to depression. While serotonin is a well-known brain neurotransmitter, an estimated 90 per cent of the body’s serotonin is actually made in the digestive tract.

New research published this year shows that certain bacteria in the gut are important for the production of peripheral serotonin1. As well as having a role to play in mood, altered levels of peripheral serotonin have been linked to diseases such as irritable bowel syndrome, cardiovascular disease and osteoporosis.

Peripheral serotonin is produced in the digestive tract by enterochromaffin (EC) cells. The researchers found that the EC cells from germ-free mice produced approximately 60 percent less serotonin than did their peers with conventional bacterial colonies. When these germ-free mice were recolonised with normal gut microbes, the serotonin levels went back up – showing that the deficiency in serotonin can be reversed.

This demonstrates that the EC cells appear to depend on microbes to make serotonin – or at least a large portion of it.Kombucha

The study’s authors also observed that only specific species of bacteria interact with EC cells to make serotonin. This suggests that much of the body’s serotonin relies on particular bacteria to produce serotonin.

Serotonin is important for many aspects of human health. These findings point to the potential use of gut microbes to drive positive changes in our biology, including our mental health.

Health tip: More and more, science is finding direct connections between gut health, brain function, and overall wellbeing. So for optimal health, wellness and happiness, listen to your gut!


Yano, Jessica M. et al. (2015), Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis Cell , Volume 161 , Issue 2 , 264 – 276. DOI:

Kat Boehringer 
Freelance journalist and editor 

Kat Boehringer specialises in health communications including health writing, health promotions, and social media management. In her spare time she works as a massage therapist and aspiring novelist. Connect with her at LinkedIn.