The precise cause of Irritable Bowel Syndrome (IBS) is unknown. Being diagnosed with IBS can be misleading for people because IBS is not a disease per say but rather a group of symptoms that can be caused by multiple factors. One person’s cause of IBS could be entirely different from another person and therefore require very different treatment approaches.  Furthermore, people suffering from IBS could be afflicted by two or more different causes and may require a multi-pronged treatment approach. There will never be one drug that cures everyone’s IBS because sufferers require an individualized treatment that addresses their specific underlying causes of IBS. Determining the causes of IBS is essential to develop an effective treatment strategy.

1. Food causes of IBS

IgG Food sensitivities

Food sensitivities are different than food allergies. Although they both involve the immune system, allergies involve IgE antibodies while food sensitivities involve IgG antibodies. When someone consumes excess amounts of their food sensitivities the IgG antibodies form immune complexes that stimulate inflammation and corresponding symptoms. Several studies show a connection between food sensitivities and IBS symptoms including bloating, abdominal pain, diarrhea and/or constipation.1–3

In theory, any food can cause food sensitivities and people typically are sensitive to multiple foods. Common foods that produce the highest reaction include milk, egg white, gluten, and yeast.1,4 However most people have multiple food sensitivities and they could be caused by any number of foods.  A simple blood test can be used to determine your food sensitivities. Consult a naturopathic doctor to get your food sensitivities tested.

Excess sugar

Excessive sugar intake may also cause or worsen IBS symptoms. In particular short chain carbohydrates (SCA) also referred to as Fermentable, Oligo-, Di-, Mono-saccharides And Polyols (FODMAP) have been implicated as one of the causes of IBS. These SCA are slowly digested and absorbed by your body, thus they remain in the bowels. This can have an osmotic effect and pull water into the bowels resulting in diarrhea. In addition, bacteria residing in your bowels can ferment these sugars producing bloating and flatulence, and even abdominal pain.5

Some people find relief following the FODMAP diet that restricts the consumption of these sugars. Some food items which are high in these types of sugar are summarized below  Table 1.)

Table 1.  Sugars causing IBS symptoms.

[ultimatetables 34 /]


2. Infectious causes of IBS

In some patients with IBS, the symptoms begin suddenly. There may be a history of travel, camping or getting food poisoning. In fact, having infectious enteritis or foodborne illness causes a fourfold increase in the risk of IBS.6 IBS may also be brought on by antibiotics because they disrupt gut flora. In some cases, people may not associate the onset of symptoms with any particular change. Regardless if you suddenly develop IBS or it gets significantly worse, you should rule-out an infectious cause of IBS.

Several different types of microorganisms can cause IBS including bacteria, parasite, and fungi. Because different microorganisms are affected by different treatments, it is important to determine which microorganism is responsible.


Billions of bacteria live in symbiosis in our large intestine and do not cause problems. In fact, good bacteria (probiotics) can even help with IBS.7 However certain pathogenic bacteria can cause IBS including Campylobacter jejuni8, Shigella sonnei,9 Escherichia coli,10 Salmonella,11 Clostridium difficile.12 This usually occurs after eating contaminated food or water. Stool samples can be used to rule this out.

In other cases, bacteria can migrate to the small intestine where they do not typically reside and cause small intestinal overgrowth (SIBO).13 Many symptoms associated with SIBO overlap with IBS symptoms including abdominal pain, bloating, gas, diarrhea, and constipation.14 Performing a “breath test” can determine if SIBO is the cause of IBS.


Several different types of parasites have been implemented in IBS including Blastocystis species15,16 and Giardia17,18. Both will produce stomach pain, bloating, cramping and diarrhea. Gut parasites are completely different than bacteria and typically do not respond to antibiotics and therefore require antiparasitic drugs or herbs.


Candida is responsible for vaginal yeast infections. They can also colonize the intestines and produce symptoms associated with IBS.19,20 These yeasts are not affected by antibiotics and require antifungal herbs to kill them.

3. Stress & Sleep

Elevated stress and sleep deprivation are two causes of IBS that usually aggravate other factors. Stress is known to cause gastrointestinal symptoms due to the alteration of the brain-gut interactions.21–23 Specifically, stress induces increases in gastrointestinal permeability, negative effects on gut microbiota, and changes in gastrointestinal secretions. Also, stress suppresses immune function that can affect your ability to find gut infections.

Poor sleep quality may also cause IBS.22,24 Sleep deprivation promotes an inflammatory response that can then lead to the development of gastrointestinal symptoms.25,26

Summary – Causes of IBS

Many people suffer from chronic IBS because they have not determined and treated the causes of their symptoms. My advice is if you suffer from IBS start by ruling out food sensitivities and try different diets for IBS. Consult a naturopathic doctor for help. Taking natural antibiotics and antifungal herbs can help as well. Consider performing a breath test to rule-out SIBO.  In some cases, a stool sample to rule out other possible infectious may be warranted. Finally, although stress and sleep are unlikely the primary causes improving both will help.

Author: Matt Gowan, BSc, ND
All images are copyright of Matt Gowan ©2017 Reference

Disclaimer: This content is subject to change. The information is intended to inform and educate; it does not replace the medical evaluation, advice, diagnosis or treatment by a healthcare professional. © 2017 NDAssist Inc. and/or its affiliates. All rights reserved.

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