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Unraveling the Mystery: What Causes IBS?

IBS is one of the most common functional gut disorders; it is thought to affect about 12% of the population. However, figuring out exactly what causes IBS has been an on-going challenge. Recent studies have given us some clues, showing that IBS is caused by a multitude of factors. Let’s dive into some of the potential causes of IBS.

Changes in the Gut Microbiota

Studies have found that there are differences in the composition of the gut microbiota between individuals with IBS and those without. Reports have linked the development of IBS to dysbiosis, a decrease in microbial diversity, and less “good bacteria” and more “bad bacteria”, potentially as a result of intestinal permeability or “leaky gut”.

Changes in the bacteria living in your gut might play a role in causing irritable bowel syndrome (IBS) by affecting the following:

  • Gut immunity and integrity: The balance of bacteria in your gut can affect how well your immune system works in your gut and how strong the lining of your gut is.

  • Gut neuromuscular junction: This refers to the connection between nerves and muscles in your gut. Changes in gut bacteria could affect how well this connection works, potentially leading to symptoms of IBS.

  • Gut-brain axis: This is the communication pathway between your gut and your brain. Alterations in gut bacteria might influence this pathway, impacting how your brain perceives and responds to signals from your gut, which can contribute to IBS symptoms.

There is evidence that suggests that probiotics, which are beneficial bacteria, can help alleviate symptoms of IBS by improving gut sensitivity, reducing intestinal permeability (leakiness), and decreasing inflammation in the gut. Further, what you eat can change the types of bacteria in your gut, emphasizing the importance of diet in managing IBS.

Altered Mobility: How Your Digestive System Moves

People with irritable bowel syndrome (IBS) often experience changes in how their gut moves, which can lead to symptoms like diarrhea, constipation, or both. Stress plays a big role in causing these changes through a communication pathway called the gut-brain axis. One of the key factors involved is serotonin, a chemical in the body that helps regulate gut movement. In IBS, people with diarrhea tend to have high levels of serotonin, while those with constipation tend to have low levels. This imbalance in serotonin can contribute to the different symptoms experienced by people with IBS.

Stress and Alterations in the Gut Brain Axis

The communication between the gut and the brain, called the gut-brain axis (GBA), can be disrupted in conditions like irritable bowel syndrome (IBS). The GBA involves various systems, including neural, endocrine, immune, and gastrointestinal components. Changes in the GBA are linked to neurological and gastrointestinal disorders like IBS and inflammatory bowel diseases. Anxiety and depression are common in IBS patients, but it's unclear whether they cause IBS or vice versa. 

Stress is a major factor affecting the gut-brain axis, impacting gut function, immune responses, and gut bacteria composition. Stress can trigger the release of certain chemicals that affect gut health. Managing stress is crucial in treating IBS, along with addressing other psychological factors like abuse and trauma that may contribute to gut-brain interactions and IBS development.


What you eat and how your body breaks down food can have a big impact on how your gut works. This includes, how quickly food moves through the gut, how permeable your gut lining is, what type and how much bacteria live in your gut, visceral sensation, brain-gut interactions, immune regulation and neuro-endocrine function. Therefore, following a diet that limits foods that cause these changes and includes foods that can help correct dysbiosis and support a healthy gut lining, can help prevent or manage IBS.

Infection: When was the last time you had the stomach flu?

One of the most common causes of IBS is experiencing a gastrointestinal infection, caused by bacteria, a virus, or a parasite, this is called post-infectious IBS. Following a bout of the stomach flu or travelers diarrhea some people will experience changes in their gut, such as intestinal inflammation, intestinal permeability, changes in gut immune responses, and in serotonin levels.

You can develop post infectious IBS 2-3 years after their initial infection, making it hard to link back to. Worse, post-infectious IBS can last up to 10 years after the initial infections.

Risk factors for PI-IBS include young age, female gender, depression, anxiety, and prolonged initial infection with fever.

Hereditary Factors: Is It in Your Genes?

It has been found that there can be a genetic component to developing IBS. A number of single nucleotide polymorphisms (SNPs) have been found in people with IBS. Researchers have also found some gene mutations in people with IBS, such as mutations in the SC5NA gene, which is associated with experiencing abdominal pain. However, the role of genetics in the development of IBS still remains obscure.

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Understanding why IBS happens is important for finding ways to manage it better. By knowing that it's caused by lots of different things, we can try different treatments that target each part of the problem. There is still a lot to learn, but in the meantime at least there are known diet and lifestyle strategies that can help improve IBS symptoms. These strategies are complex and best implemented with the support of a dietitian or naturopath who specializes in gut health. 

Sam Thompson Nutrition has helped dozens of people tackle their IBS symptoms and regain their quality of life, book a discovery call today to find out how.


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Thabane M, Marshall JK. Post-infectious irritable bowel syndrome. World J Gastroenterol. 2009 Aug 7;15(29):3591-6. doi: 10.3748/wjg.15.3591. PMID: 19653335; PMCID: PMC2721231.


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