The Brain, Gut and IBS


Irritable bowel syndrome (IBS) is a very common, long-term condition which roughly 1.5 in every 10 people have in the UK alone. I am one of these people. Symptoms can include pain and discomfort/cramping in your lower abdomen, bloating, and changes to bowel habits (moving between bouts of constipation and diarrhoea). More severe cases can lead to sickness, headaches and increased tiredness (which I can attest to, especially if you’ve been up all night in discomfort). If you believe you may have IBS it is worth a trip to the GP, as there are many avenues to discuss which can alleviate discomfort and to rule out other conditions such as Crohn’s disease and IBD (irritable bowel disease). Unfortunately, many things are linked to causing IBS and each individual could have a varying combination of factors which contribute to their symptoms. Some commonly accepted examples include sensitivity to certain foods, changes to the gut microbiome, inflammation, anxiety and depression. The final two require further explanation through our brain-gut link.

There are currently a range of treatments available to IBS sufferers such as dietary management and exclusions, medication for symptoms such as cramping, and lifestyle changes which can range from weight loss to therapy. As you can see, there are a wide range of options, however, these usually treat symptoms (such as cramping and bloating) rather than a root cause – i.e. what is causing the flare-up? Anecdotally, I was treated with medication for cramping, but to little avail. Whilst there are certain foods I avoid (or time my consumption so I can still enjoy things like an ice cream milkshake without panicking), I still get flare-ups which are completely unrelated to food but equally debilitating. For me, these are always in conjunction with an anxious situation, ranging from worrying about travel the night before a journey, to giving a lecture. So, after years of trying to manage IBS, what can new research tell me about the link between our brains and guts.

In 2015, researchers reviewed the data available which evidenced a link between our brains and guts. Here, they highlighted links between both the emotional and cognitive centres of the brain and intestinal function, summarising that our gut microbiome can influence our brain and vice versa. The researchers termed this the gut-brain axis (GBA), a communication network which connects the organs physically and biochemically. Neurons physically connect the brain and gut via our central nervous system (CNS). One of the largest nerves connecting the two sites is the vagus nerve, which sends signals in both directions. Studies in both mice and humans have indicated the importance of the vagus nerve in IBS symptoms, finding both IBS and Crohn’s sufferers had reduced vagus nerve function when compared to a normal value. Aside from this physical link, our GBA is connected biochemically by neurotransmitters, the chemical messengers which transmit signals along nerve cells via the nervous system. We usually associate neurotransmitters as being produced in the brain however, many neurotransmitters are also produced by the microbes that live in our guts. For example, a large proportion of our serotonin (i.e. a neurotransmitter which contributes to happiness) is produced in our guts! Another gut-microbe-produced neurotransmitter is gamma-aminobutyric acid (GABA), which is linked to aiding the control of feelings of fear and anxiety. Some studies (using mice) suggested that increasing GABA production, by taking probiotics, reduced anxiety and depression-like behaviour. If you’re interested in further GBA research check out this great article from 2020: https://www.healthline.com/nutrition/gut-brain-connection.

In November 2021 an international study, comprising of over 40 institutions and more than 50,000 participants, attempted to understand if genetics played a role in the origins of IBS. The study compared the genetic data from over 50,000 IBS sufferers and more than 430,000 control subjects (i.e. those who do not have IBS) of European ancestry (read my previous article to understand why this can cause problems: Sex and Ethnic Bias in Pharma). Overall, the study found the heritability of IBS was low (i.e. do our genes influence the chance of developing a condition), suggesting environmental factors such as diet and stress, which can be shared by family members, are more influential. However, researchers did find six genetic differences were more common in IBS sufferers than control participants. Interestingly, these genes were not expressed in the gut/bowel, but instead expressed in the brain and nerves which supply the gut (e.g. the vagus nerve). Professor Mike Parkes of the University of Cambridge, co-senior investigator on the study, said “our study shows [IBS and anxiety disorders] have shared genetic origins, with the affected genes possibly leading to physical changes in brain or nerve cells that in turn cause symptoms in the brain and symptoms in the gut.” Finally, the study also found people who suffer with IBS and anxiety were more likely to have had frequent antibiotic use in childhood (I spent my first 4 years or so constantly on and off antibiotic courses…). The authors hypothesised frequent antibiotic use could alter “normal” gut flora, influencing nerve cell development and mood, although this requires further research. We’re already aware of the dangers of antibiotic resistance through overuse of antibiotics, such studies could provide further evidence for more controlled use.

Our study shows [IBS and anxiety disorders] have shared genetic origins, with the affected genes possibly leading to physical changes in brain or nerve cells that in turn cause symptoms in the brain and symptoms in the gut.”

Prof. Miles Parkes, University of Cambridge

It is now recognised that gut bacteria can affect brain health, so improving your gut bacteria could improve your mental health. For example, probiotics (specifically those containing the bacterial strain Bifidobacterium longum) can potentially improve mild-moderate symptoms of depression and anxiety, according to a study investigating IBS sufferers for 6 weeks (an avenue I am currently exploring myself). Some food types are beneficial for our GBA too such as, Omega-3 fats (e.g. oily fish), fermented food (e.g. yogurt and cheese – although my gut would disagree with the latter) and high-fibre foods (e.g. whole-grain, nuts, fruit etc.) which can reduce stress hormones. However, current research into the understanding of how our brains and guts are interconnected will open new ways to consider gastro-diseases and their treatment.

While You’re Here

If you are looking for more articles around gut bacteria, the nervous system or anxiety, you should follow the links below:

Are Bacteria Causing Alzheimer’s?

Alzheimer’s disease is debilitating and difficult not only for the sufferer, but also those around them. Research into this condition has been underway for many years and, with an organ as complicated as the brain, it can be difficult to pin point the exact cause of this condition. Recent studies may have, however, found a link between bacteria causing gum disease and Alzheimer’s. 

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Competition Winner – Erin

Erin is the second winner of our science writing competition, and entered the 13-15 year old category. She is 14 years old and her home country the UK. I really enjoyed Erin’s piece about reflexes, it is well written and explained everyday science perfectly. Again, very impressive for someone so young; Congratulations Erin. The following is entirely Erin’s work, enjoy…

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Anxiety: Evolutionary Help or Hindrance

Unless you are so laid back you’re horizontal, you are likely to have had the misfortune of feeling anxious at some point in your life. Whether it was a big presentation, a driving test, or a social encounter, anxiety can happen because of numerous triggers: everyone is different. In a world of social pressure and increasing recognition of mental health,  let’s understand why we get anxious and the symptoms that come with it.

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