Do you really have a second brain in your gut?

Written by Megan Colwell


When we talk about ‘gut health’ we’re talking about a complex system with three inseparable components.

  1. the gut cells themselves that make up the gastrointestinal tract from our mouth to our anus
  2. the nerves and nerve cells (neurons) that are interwoven with our gut cells – known as the enteric nervous system (ENS) – and that communicate with our brain
  3. the microbes or trillions of bacteria that live in every nook and cranny of the gut

Together, these three entities – our gut, its nerve cells and its microbial residents – form an integrated information exchange system known as the brain-gut-microbiome axis. This might seem self-evident to you today, but only a few decades ago, the gut was considered to be nothing more than a tube that broke down and absorbed food and eliminated what we didn’t need.

We now know that the gut gathers information from the components of our food and from our environment every second of the day. Not only does the gut receive information from our external environment – through everything we ingest and from the microbes that live in it – the gut also receives information from our internal environment – our brain and neighbouring organs. All this information then influences the gut’s production of hormones, neurotransmitters and enzymes. In turn, these signalling molecules influence our physical, mental and emotional health.

Messages travel between the brain and the gut via three pathways (that we know of so far):

  1. the blood stream
  2. the immune system
  3. a long large nerve called the vagus

The gut’s enteric nervous system is sometimes described as a ‘second brain’ because it consists of two thin layers of more than 100 million neurons lining its walls from oesophagus to rectum. That’s about the same number of neurons as in the brain of a cat! As well as controlling our digestive processes, the enteric nervous system modulates gut activity in response to different emotional states.

Our gut mirrors every emotion that arises in our brain. Conversely, what’s going on in our gut can profoundly affect our mental health. Different emotions are characterised by different chemicals in the brain – serotonin when we’re happy, cortisol when we’re stressed – and these chemicals lead to a distinct response in our gut and its microbes. In fact 95% of the body’s serotonin is stored in the gut!

Therefore, how you feel when you eat – relaxed, anxious or angry – influences how your gut and its microbes metabolise your food. If you eat while stressed, the resulting cortisol not only stimulates your appetite and your desire for sugary foods, it leads to fat deposition around your abdomen. That’s the effect of the hormone cortisol.

When you eat in a calm state, you activate your left prefrontal cortex and your parasympathetic nervous system, both of which lead to better digestion, more rational decision making and less likelihood of storing the calories as fat!

Your emotional state while you eat is just as important as what you eat. So relax and enjoy your meal.