The causes of irritable bowel syndrome (IBS) are often difficult to diagnose. While previous research suggested that small intestinal bacterial overgrowth (SIBO) might be responsible for up to 70% of IBS cases, this theory has been challenged by recent studies.
The debate: Is SIBO the primary cause of IBS?
A recent paper has challenged the hypothesis that IBS may be caused by SIBO and that breath testing for SIBO may not be a reliable assessment to confirm this differential diagnosis.
The paper highlights that many human disorders, including gut-brain interaction disorders (previously known as functional bowel disorders like IBS), are strongly influenced by interactions between microbes and the host in the intestinal tract.
SIBO is a condition of overgrowth of bacteria in the small intestine and as such, is disruptive to the efficiency of gastrointestinal function. Preparation for SIBO breath testing is conducted after a day of dietary modification, a 12 hour fast overnight, followed by 3 hours of breath sampling, every 20 minutes.
Normally, the time it takes for a sugar solution (like lactulose, glucose, or fructose) consumed during SIBO testing to travel from the mouth to the cecum (where the small intestine meets the large intestine) is typically around 100 minutes, a measure known as orocecal transit time.
However, in people with IBS, especially those with diarrhoea-dominant IBS (IBS-D), the transit time is often much faster – closer to 70 minutes. This quick transit can result in the early detection of gases in the breath test, which might not indicate SIBO at all, but simply that the sugars have already reached the large intestine. This can lead to a false positive diagnosis of SIBO.
This raises concerns about using lactulose as a testing substrate, as it may accelerate transit time. Glucose, absorbed quickly in the upper small intestine, could be a better option for identifying bacterial overgrowth linked to SIBO. However, if bacterial overgrowth occurs in the lower small intestine, glucose may miss it, leading to a false negative result.
The real concern is that people may be misdiagnosed with SIBO and then prescribed unnecessary antibiotics, which could harm an already sensitive digestive tract.
Re-evaluating IBS treatment: Beyond SIBO testing
So what can we do? Â
We know that other causes of IBS symptoms must be considered in the assessment and treatment of IBS. The presence of stress hormones, anxiety, depression, pH of the GIT, the actions of bile acids, sufficient stomach acid, microbiome health, lifestyle and diet can all influence the management of IBS symptoms and should be considered in patient care.
Interpretation of SIBO test results is therefore vitally important and should be conducted by a skilled practitioner who is very familiar with integrating a patient’s case history, current symptoms and details surrounding their testing experience.
At Melbourne Functional Medicine, we approach IBS with a comprehensive, individualised strategy that goes beyond SIBO testing alone. By addressing the full spectrum of factors – diet, lifestyle, stress, gut health, and more – we ensure that each patient receives a tailored plan for long-term relief. With skilled practitioners interpreting test results and integrating them with your unique case history, we provide a more accurate diagnosis and effective treatment pathway.
If you’re ready to take control of your IBS and explore personalised care, book a discovery call. Together, we’ll chart a course to lasting gut health and overall well-being.
