What Causes Irritable Bowel Syndrome (IBS)?

In the eyes of a naturopathic doctor, irritable bowel syndrome is an incomplete diagnosis. It doesn’t tell us WHY your symptoms are occurring. Alternatively, it’s more of a grouping of symptoms with an unknown cause. So what is the cause?

Abdominal pain along with changes in bowel movements such as diarrhea or constipation (or both!), are the hallmarks of irritable bowel syndrome (IBS). These symptoms without any link to a specific or unique disease defines IBS. Often times additional symptoms are also present. Symptoms of IBS may include:

  • Bloating

  • Gas

  • Abdominal discomfort

  • Changes in bowel movements

Approximately 10-20% of people struggle with IBS (1). It is so common. But it doesn’t have to be the norm. Getting to the root cause of your IBS is the first step.

Of those people with IBS, studies show that over a third will test positive for small intestinal bacterial overgrowth (SIBO) (2).

What is SIBO?

As the name suggests, SIBO is an overgrowth of bacteria in the small intestine. Typically the large intestine harbours the majority of our gut bacteria (with numbers into the tens of trillions) and the small intestine contains relatively small numbers of bacteria (around a hundred million). When there is an overgrowth of bacteria in the small intestine, or an imbalance of “good” and “bad” bacteria, this is when issues may occur. Bloating is a leading symptom of SIBO and occurs when bacteria in the small intestine produce unwanted gas. The small intestine is not well equipped for the elimination of gas and so this gas accumulates and may lead to bloating.

How do you know if your IBS is caused by SIBO?

To determine whether SIBO is the root cause of IBS, this requires a test called a lactulose breath test. This is an at-home test you can request through a naturopathic doctor or other healthcare provider. Your healthcare provider will help interpret the results, which will show whether or not you have small intestinal bacteria overgrowth and whether those bacteria are hydrogen or methane gas producers. Knowing the type of gas producers present helps to guide appropriate treatment.

Other contributing factors to IBS

Although SIBO may be one of the more common underlying explanations of IBS, other contributing factors may include:

  1. Dysbiosis - general imbalance of the gut microbiota, not necessarily specific to SIBO. Gastrointestinal infection (whether viral, bacterial, or parasitic) may be a trigger for IBS symptoms resulting in post-infectious IBS. In some people, the use of probiotics has been shown to reduce symptoms such as bloating and gas (3). However it’s important to note that worsening of symptoms with probiotics is something I see clinically as a sign of SIBO, especially if those probiotics contain inulin or other prebiotics.

  2. Food triggers - typically those foods that are more difficult to digest are implicated such as milk and dairy products, wheat products, and red meats. Many people that have been tested negative for celiac disease (an autoimmune disease towards gluten) still report a non-celiac gluten sensitivity. Other food triggers may include FODMAP foods such as onions, beans or cabbage. These FODMAP foods may be aggravating because they feed unwanted bacteria in the small intestine (another sign suggesting SIBO).

  3. Stress - there is a strong correlation between stress disorders and and IBS (4). There are two sides to our nervous systems: “fight or flight” and “rest and digest”. When the body is under stress in the “fight or flight” mode, it is not concerned with digestion and so there may be a reduction in digestive processes such as stomach acid production making breakdown of foods more difficult.

If you’re interested in understanding WHY you have a diagnosis of IBS, come see me at Juniper Family Health (778-265-8340) in Victoria BC. Online booking available here.


1. Lehrer, J. (2019). Irritable Bowel Syndrome (IBS). Medscape: https://emedicine.medscape.com/article/180389-overview

2. Mann, N., Limoges-Gonzales, M. (2009). The prevalence of small intestinal bacteria vergrowth in irritable bowel syndrome. Hepato-gastroenterology, 56(91-92), 718-721.

3. El-Salhy, M. (2012). Irritable bowel syndrome: Diagnosis and pathogenesis. World Journal of Gastroenterology, 18(37), 5151-5163.

4. Grundmann, O., Yoon, S. (2010). Irritable bowel syndrome: Epidemiology, diagnosis and treatment: An update for health-care practitioners. Journal of Gastroenterology and Hepatology, 25(4), 691-699.