IBS From A Functional Medicine Approach
Irritable Bowel Syndrome (IBS) is one of the most common yet misunderstood gastrointestinal conditions. It affects 15% of the world’s population, interfering with daily life in a way that feels unpredictable, frustrating, and, at times, isolating.
During IBS Awareness Month, the conversation tends to focus on symptom management. What to eat, what to avoid, how to reduce bloating. While this has its place, it often misses a more important question: why is this happening in the first place? This is where a functional medicine approach becomes valuable. Rather than viewing IBS as a diagnosis, it looks at it as a reflection of underlying imbalances, a signal from the body, not the root issue itself.
What is IBS?
IBS is considered a disorder of the gut-brain axis, the constant communication network between the digestive system and the brain. When this communication becomes disrupted, symptoms such as abdominal pain, bloating, distention, and changes in bowel habits (constipation, diarrhoea, or both) can start to appear. This definition, while accurate, is still surface-level – in practice, IBS is rarely one thing. It’s usually the result of multiple overlapping factors, each contributing to how symptoms show up and persist over time.
What causes IBS? Looking at what sits underneath
In functional medicine, one of the most common starting points is digestive function. If stomach acid, enzymes, or bile flow are suboptimal, food isn’t broken down properly. This creates the perfect environment for fermentation, leading to bloating, gas, and discomfort. Supporting digestion can be surprisingly simple, but often overlooked,eating in a relaxed state, chewing food properly, and including bitter foods to stimulate bile flow can make a meaningful difference before even considering supplements.
Then there’s the gut microbiome. Dysbiosis, an imbalance between beneficial and less beneficial microbes, is a key driver in many IBS cases. But this is where nuance matters. There isn’t a universal fix, some people do well with probiotics, others feel worse. Some benefit from targeted antimicrobial support. In most cases, it’s a gradual, personalised process rather than a quick intervention.
An increasingly recognised contributor is Small Intestinal Bacterial Overgrowth (SIBO). While it’s often framed as just a bacterial issue, in reality it’s usually a motility issue first. When the movement of the gut slows down, bacteria that should remain in the large intestine begin to overgrow in the small intestine - this is why simply “killing the bacteria” rarely leads to long-term results. Unless gut motility is supported, symptoms tend to return.
Closely related to SIBO is Intestinal Methanogen Overgrowth (IMO), where methane-producing microorganisms (archaea rather than bacteria) are present in excess. While SIBO is more commonly associated with hydrogen production and symptoms such as bloating, abdominal discomfort, and diarrhoea (often seen in IBS-D), methane production in IMO tends to slow gut transit, leading to constipation, bloating, and a feeling of incomplete evacuation, which is more commonly associated with IBS-C. Understanding whether hydrogen or methane is the dominant gas can help explain symptom patterns and guide a more targeted approach.
Hormonal health also plays a role, particularly thyroid function. An underactive thyroid slows down gut transit, often leading to constipation and, in some cases, contributing to SIBO. Supporting thyroid health isn’t just about medication, it often involves ensuring adequate intake of key nutrients such as iodine, selenium, zinc, and iron, alongside addressing stress, inflammation, and blood sugar balance.
And then there’s stress (of course, doesn’t it impact everything) - not in the vague, overused sense, but in a very real physiological one. Chronic stress shifts the body into a survival state where digestion is no longer prioritised. Stomach acid production drops, enzyme output decreases, and gut motility becomes disrupted. Over time, chronic stress can also increase gut sensitivity and alter the gut microbiome, creating a feedback loop where symptoms and stress reinforce each other.
The lesser talked about drivers
One of the most common causes of IBS is food poisoning. Post-infectious IBS (PI-IBS) can develop after a bout of gastroenteritis, sometimes months after the initial infection has resolved. What’s particularly interesting here is the autoimmune component. In some individuals, the body produces antibodies, known as anti-vinculin antibodies, which interfere with the nerves that regulate gut motility. This helps explain why symptoms can persist long after the infection itself has cleared, and why PI-IBS leads to SIBO in most cases.
Another layer that is becoming increasingly relevant is histamine intolerance and mast cell activation. Histamine is a natural compound involved in immune responses, but it also plays a role in gut function. When histamine levels build up, either due to reduced breakdown or increased release, it can contribute to symptoms that resemble IBS: bloating, diarrhoea, abdominal pain, as well as systemic symptoms like headaches, skin reactions, or sinus issues. In some cases, this overlaps with Mast Cell Activation Syndrome (MCAS), where mast cells release inflammatory mediators in an exaggerated or inappropriate way. This can heighten gut sensitivity, disrupt motility, and make the digestive system far more reactive to foods, stress, and environmental triggers.
A different way of looking at IBS
What becomes clear through the functional medicine lens is that IBS isn’t a condition with a single cause and solution. It’s a label given to a cluster of symptoms that can arise from very different root causes. This is why two people with the same symptoms can respond completely differently to the same intervention. It’s also why symptom-focused approaches, while helpful in the short term, often fall short in the long term.
A functional medicine approach doesn’t promise quick fixes, but it does offer something perhaps more valuable: a framework for understanding why symptoms are happening, and a way to address them in a more targeted way.
Words by Marilia Chamon for The Well Edit.
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