IBS & The Gut Brain Axis

Resource by

Joanna Baker


28 Sep 2022

Reading Time

5 mins


Worldwide, its estimated that about 10-15% of people have Irritable Bowel Syndrome (IBS). This means that if you know 7 people, it’s likely that one of them has IBS and is also living with unpredictable, painful and embarrassing gut symptoms. While IBS is most definitely not all in your head, the gut brain axis and visceral hypersensitivity (we will explain what this is in a minute) both play a central role in the physiology of IBS symptoms and their severity. Let’s take a look at what this all means.


What is IBS?

IBS is a functional condition. This means that the gut is essentially healthy, but appears to not function as it should resulting in symptoms like bloating, gas, abdominal pain and altered bowel habits (constipation or diarrhoea or alternating between the two). These symptoms can be caused by other conditions though, so IBS is only diagnosed once medical causes (e.g. coeliac disease or inflammatory bowel diseases) are excluded.


What is the gut brain axis?

If you’ve ever experienced butterflies in your stomach, then you’ve experienced the gut-brain axis in action. The vagus nerve is a two way super highway that connects the head brain and the gut brain. It carries messages from the brain to the gut and intestines to control digestion. At the same time, it also carries messages from the gut to the brain reporting back on information collected by the nerves in and around the gut.

It’s thought that in IBS, the gut “over communicates” with the head and that some of the messages from the gut nerves get scrambled, resulting in the brain thinking that normal digestive processes as if they are dangerous, which can trigger unpleasant gut symptoms.


What is visceral hypersensitivity?

The viscera refers to internal organs in the abdomen like your stomach and intestine. Being hypersensitive in this area means that you have high sensitivity and experience more sensation or pain than someone with low visceral sensitivity.  To understand this and its relationship to IBS, it helps to look at how pain messages are sent and how they are processed in the body.

You might be surprised to know that all pain originates in the brain, regardless of where it is felt. Your five senses (touch, smell, sight etc) are constantly collecting information from about what is going on in your outside world. This information is collected and sent to the brain for interpretation. The brain considers the information and weighs it up against past experience,  current situation and future expectation to determine if it should be concerned about anything. If the brain determines that something is dangerous (e.g. heat from a stove element), it will send pain messages to get your attention and get you to change the situation. This makes pain a complex protective mechanism designed to keep you safe.

Just like your senses collect information from the outside world, the nerves in and around your gut collect information about your inside world and relay that to the brain via the vagus nerve, or gut brain axis.

If you combine hypersensitive nerves that over respond to normal digestive processes and an over active gut brain axis, then you can imagine that the brain is getting over run with all sorts of information about digestion. This can make the brain more concerned about digestion than necessary.

When you add stress on top of this overactive response it can add another layer of complexity. If you are stressed then you activate fight or flight mode, putting all of the nerves in your body (including those in the gut) on higher alert and the brain will be more responsive. This can increase visceral hypersensitivity and the messages flowing through the brain-gut axis which means stress can exacerbate IBS symptoms.


What about FODMAPs?

So where do FODMAPs fit when it comes to the brain-gut access? FODMAPs are small sugar or carbohydrate molecules that naturally occur in a range of foods. When we eat foods that contain FODMAPs, they pass through the stomach like normal, but when they get to the small intestine they are not absorbed. This means they continue their path along the digestive tract to the colon or large intestine. On arrival in the colon, FODMAPs are then involved in two processes:

  1. They attract water into the intestines causing loose or watery stools
  2. They are fermented by the healthy bacteria that live there creating gas

In many cases this is a normal process, and oligosaccharides (fructans & GOS) in particular are not absorbed by anyone. Everyone who eats onion and garlic, for example, will create gas in their intestines, however it depends on the sensitivity of the nerves in your gut and your gut brain axis as to if this will cause pain for you or not. This means that although two people can eat the same meal and digest it in the same way, one can be in a world of pain while the other is chuckling about how much farting they are doing today.


What does all this mean for your IBS?

The really cool thing about the nervous system is that it’s not hardwired like the electrics in a house. We have this thing called neuroplasticity, which means that the nerves in the gut and the gut brain axis can learn new tricks. Research shows that gut directed hypnotherapy, mediation, yoga, cognitive behavioural therapy and managing stress can all help to calm the nerves and the gut brain axis. If you’re already on a Low FODMAP diet that’s great! If you are still getting symptoms or are having trouble expanding your diet, you might like to think about adding some behavioural strategies to your IBS toolbox.


Final thoughts

In a nutshell, IBS doesn’t have one cause. Instead, there are a range of factors that are involved in IBS symptoms. As a dietitian who specialise in IBS, I see a lot of people managing it in a lot of different ways. The one constant though, is that those who use a range of strategies are the ones who get best results.

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