Do you really have a second brain in your gut?

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.

* To read other HEB’s in the gut series click below:

Showing 6 comments
  • John Fox

    Always entertaining and informative.

    • Helena Popovic

      Thank you, John!

  • Pam barrett

    Thank you for your emails. Years ago Naturopaths spoke about leaky gut syndrome. Very interesting medically they are now agreeing to this.

    • Helena Popovic

      Hello Pam,

      Yes, when I was in medical school, leaky gut syndrome was not recognised. Now doctors are calling it ‘intestinal hyper-permeability’ because it is characterised by loosening of the tight junctions between the cells that form our gut lining. We’re still unravelling the causes but it’s often associated with severe gut infections, long courses of antibiotics, frequent consumption of processed foods or having specific food sensitivities. Symptoms of leaky gut syndrome include bloating, pain, gas, cramps, fatigue and a higher risk of autoimmune diseases, allergies, obesity and mental health issues.

      One way to diagnose leaky gut syndrome is to drink a mixture of mannitol and lactulose. Mannitol is a tiny molecule and is therefore able to pass through a healthy gut wall into your blood and into your urine. Lactulose is much larger and should not fit through an intact gut lining. After consuming the drink, your urine will be tested for the amount of mannitol and lactulose it contains. If your gut wall is functioning as it should, your urine will contain mannitol but very little lactulose.

      Best wishes,

  • Anthony Harris


    Can you recommend a healthy probiotic

    • Helena Popovic

      Hello Anthony,

      The theory behind probiotic supplements is appealing but largely untested. The presumption is that living probiotics favourably change the bacterial balance in our gut. However scientists have not yet worked out what constitutes an ideal microbial population. In addition, everyone is unique, and the bugs that I need might be completely different to the bugs that you need. At best, the makers of probiotics are making intelligent guesses about what they should put in their products, and what effect they might have on a person’s symptoms. Some people swear by probiotics while others find they make no difference at all. Based on the scientific evidence currently available, my best advice is to try a few different probiotics and observe the effect they have on your body. If you find that your symptoms improve or you feel subjectively better, you may have found something that works for you.

      To reiterate, I am not dismissing probiotics, I am simply making the point that developing them is still at an experimental stage. To date, several studies support the use of probiotics to prevent Clostridium difficile and certain strains of E.coli infection. Lactobacilli-containing probiotics are showing promise in helping to alleviate depression.

      For now, I prefer to eat probiotic foods such as natural yoghurt, sauerkraut, kimchi, miso, tempeh, kombucha, kefir and pickles. Best of all, learn to make your own probiotic fermented foods. Take a look at the wonderful book by Holly Davis: ‘Ferment – A guide to the Ancient Art of Culturing Food’.

      It’s also a good idea to eat foods that contain prebiotics. Prebiotics are compounds that stimulate the growth of ‘good gut bugs’. Eaten together with probiotics, prebiotics increase the chances that the probiotic will take hold, reproduce and remain for longer in your intestine. Foods rich in prebiotics include garlic, onions, leek, asparagus, artichoke and endive.

      Bon apetit!

Leave a Comment

Contact Us

We're not around right now. But you can send us an email and we'll get back to you asap.

Not readable? Change text. captcha txt