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The Gut-Brain Connection

The Gut-Brain Connection

The gut is a fascinating part of our bodies. It’s crawling with all manner of goggas, as many as 500 different species of bacteria that weigh almost 1.5kg in our digestive tract! This ecosystem of critters works together to digest our food, absorb the necessary nutrients, excrete toxins and regulate our hormonal functions.

And this is what we thought the purpose of the gut was. And it is. But what we now also know is that there is a very intimate relationship between the gut and the brain!

Feeling butterflies in your stomach before a presentation or stressful situation, getting stomach cramps and the urge to run to the loo every five minutes before a race, stress eating and the like are all evidence of our bodies getting signals from an unexpected place: your second brain. Inside of our digestive system, this second brain that resides in your gut is changing how we view the link between digestion, mood and brain health.

This second brain is called the enteric nervous system (ENS). The ENS is two thin layers containing more than 100 million nerve cells which line the gastrointestinal tract all the way from your oesophagus (swallowing) to your rectum (pooping).

The Vagus Nerve

You may have heard of the vagus nerve before and we are only now realising how important it is. Essentially, we know that there are neurons in our brains and the central nervous system that control how we behave. And wrap your head around this number, there are around 100 billion neurons in the human brain with the main aim of helping us perform our everyday functions and tasks. But neurons aren’t only found in the brain!

The gut itself contains about 500 million neurons, which are connected to your brain through the central nervous system. The biggest nerve connecting the gut and the brain? The vagus nerve. So, it makes sense that if someone suffers from irritable bowel syndrome (IBS) that we always also see reduced vagal tone, which means your vagus nerve (connecting the gut to the brain) is compromised. Conversely, a mouse study showed that if we feed mice probiotics for the gut, the stress hormone in their blood is reduced, which demonstrates just how intimately gut health and our mood and brain health are connected!

A great example: STRESS. In animal studies, stress inhibits the signals that are sent through the vagus nerve and thereby affects your brain and causes gastrointestinal problems.

Your Gut has a Brain

So, your gut has a brain! “Going with your gut” then becomes quite an interesting expression. And some scientists say it is more important and more powerful than the one that resides in our skulls. Sure, the ENS is certainly not going to take your exam for you or finish a project or help you drive a car, but it is able to control digestion (swallowing, producing enzymes to break down the food, absorbing nutrients and eliminating toxins) which is directly connected to our mood, immunity and most importantly, our brain function and health.

Until very recently, we’ve really failed to recognise that the gut is a very powerful control centre due to the fact that the gut communicates with the brain and the brain communicates with the gut. This communication and connection are called the gut-brain axis. The ENS interacts with the central nervous system (fight or flight and rest or digest) and this interaction links the emotional and cognitive centres of the brain with your intestinal function. So, when our gut is out of whack, this can be linked to slower thinking and particularly depression.

Moral of the story? We need a healthy gut to have a healthy brain and mood. How happy your gut is, however, depends on the gut microbiome (i.e. are the good and bad bacteria in balance, is your gut supported etc). With modern farming practices, stress, medications, processed food and a myriad of other assaults, we often end up with more of the bad bugs than the good ones. Not only don’t we get what we need from our food, but our brains suffer as a result of it and conditions like IBS are becoming rampant amongst us.

The good news? If you eat things that are good for your gut and supplement smartly for your microbial system, you will automatically do what is best for your health and also slow cognitive decline and improve symptoms of depression.

The Effects of a Compromised Gut-Brain Axis

Let’s look at some of the effects of when our two brains aren’t able to communicate with each other properly:


Neurotransmitters are chemical messengers in our bodies that send signals for various functions. A key function is a control in the brain over feelings and emotions. Examples of neurotransmitters include dopamine, serotonin and GABA. Serotonin, as an example, controls feelings of happiness as well as your body clock (sleep).

Many neurotransmitters are produced by your gut cells and the microbes that live in your gut, notably serotonin and GABA, which control mood, feelings of fear and anxiety. Interestingly, there are studies that show that introducing good probiotics into your system can increase the production of GABA and thereby reduce anxiety and depression.

Blood-Brain Barrier

The gut microbes produce short-chain fatty acids (SCFA), one of this being butyrate. Butyrate is important for forming the blood-brain barrier, which in turn is responsible for letting good stuff get into the brain and keep the bad stuff out. It’s your most important line of defence in brain health.

Immunity and Inflammation

Gut microbes play a very important role in the immune system and in controlling inflammation, the latter being at the heart of many chronic illnesses. In some instances, your immunity is so compromised that the immune system is switched on for too long, which leads to further inflammation, particularly that associated with Alzheimer’s disease, schizophrenia and depression.


If you have gastrointestinal issues with no obvious physical cause, then look to mental and emotional causes (therapy can be very valuable to fix a gut, believe it or not!). Psychology combines with physical factors to often be the root cause of gastrointestinal issues. This means that stress and depression affect how you physically feel in your tummy.

In addition, people with gut disorders often feel pain more severely than other people, because their brains are more receptive to pain signals. Stress, therefore, makes existing pain feel even worse!

Reducing stress and treating anxiety and depression through therapy, meditation, breathing practices and other self-care options is, therefore, key to a happy gut and brain.

Probiotics and Prebiotics

Very briefly, because we know that gut bacteria affect brain health, changing your gut bacteria can directly improve your gut health. We’ve all heard of probiotics and prebiotics, and this is how they affect our brain health:

Probiotics are live (good) bacteria that help keep the bad bacteria in our bodies in check, thereby keeping us healthy. Having the right probiotics in the body has been shown to improve symptoms of stress, anxiety and depression. For example, a study where IBS patients with mild-to-moderate anxiety or depression took a probiotic called Bifidobacterium longum for six weeks found that it significantly improved their symptoms.

Prebiotics are typically fibres that are fermented by our gut bacteria, and there are studies showing that supplementing with a prebiotic called galactooligosaccharides reduced cortisol (the stress hormone) in as little as three weeks!

How Best to Care for Your Gut

Happy gut happy life! Our guts are compromised for a variety of reasons and now that we understand how important gut health is for an OPTIMIZED brain, here are a few tips that generally aid your gut health!

  • Diet: a variety of foods, preferably organic and definitely not processed is your biggest needle mover for a healthy gut. Fruits and vegetables that are fibre rich and you are capable of digesting can be very helpful (think raspberries, broccoli and apples).
  • Fermented food: things like sauerkraut, kefir, yoghurt and kombucha are all really good for supporting your good bacteria (and should only be avoided if you have a histamine intolerance).
  • Incorporate prebiotics, probiotics and digestive enzymes as supplements, particularly if you think that you may have gut issues. Prime Self’s Gut Complex is an extremely innovative product that includes probiotics, digestive enzymes and a herb called Triphala which is amazing for gut health!

The Bottom Line

We all know those “gut-wrenching” experiences, wanting to throw up from shock or feeling a flutter of butterflies from excitement. The connection between the brain and the gut is undeniable. Our gastrointestinal tract is so sensitive to emotions of anger, anxiety, happiness and sadness and all of these can and do trigger symptoms in the gut.

Also think about this: has your mouth ever started watering just at the thought of a particular meal? That means the stomach’s juices have been released before you even started eating!

It’s a bidirectional relationship: a distressed gut signals the brain and distressed brain signals the gut.

The ENS can trigger big emotional shifts experienced by people who have IBS, constipation, diarrhoea, bloating or other stomach ailments. Conversely, the “big” brain and trauma experienced there can compromise your gut health, and it becomes a vicious cycle.

Being armed with this knowledge is the first important step in taking care of both your gut health and your brain health! Take special care of what goes on in your stomach and in your mind to truly optimise the other!

Thea Hiemstra Author
  • Thea is the founder of Neolaia – Biohacking SA and passionate about all things biohacking, functional medicine, holistic and ancestral wellness. She enjoys the occasional triathlon, is fanatic about yoga and the gym and loves n=1 biohacking experiments more than anything else! Learning about the latest in scientific research for health and wellness and applying this knowledge is what makes her happiest!
  • Instagram: biohack_sa


This information does not serve as medical advice, diagnosis, or treatment. This content is for informational purposes only and does not provide a comprehensive explanation of the different compounds. Always consult your doctor first when making any changes to medication or supplementation.

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