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What is IBS (Irritable Bowel Syndrome) and what causes it?

Updated: Dec 10, 2023

Irritable bowel syndrome is a term used for a collection of gastrointestinal symptoms that include abdominal pain, constipation and/or diarrhea, bloating and gas.

Although there are numerous causes for these symptoms, a diagnosis of IBS is typically made after other more serious conditions have been ruled out, and if the symptoms fit the following Rome IV criteria:

Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, associated with 2 or more of the following criteria: – Related to defecation (passing of stools or bowel movements) – Associated with a change in frequency of stool – Associated with a change in form (appearance) of stool

The criteria needs to be fulfilled for the last 3 months with symptom onset at least 6 months. (1, 2, 3)

What are the IBS subtypes?

IBS can be subtyped based on the frequency of abnormal bowel movements.

IBS-C is constipation predominant IBS (>25% hard stools, <25% loose stools)

IBS-D is diarrhea predominant IBS (>25% loose stools, <25% hard stools)

IBS-M involves mixed bowel habits (>25% loose stools, >25% hard stools - some can alternate between constipation and diarrhea).

IBS-U is unclassified IBS (where patients meet the diagnostic criteria for IBS but whose bowel habits cannot be accurately categorized into 1 of the 3 groups)

The Bristol Stool Chart helps to determine what is considered an abnormal bowel motion of constipation or diarrhea. Types 1 and 2 are defined as constipation or hard stools. Types 6 and 7 are diarrhea or loose stools. (2, 3)

Bristol stool chart

What other symptoms can those with IBS experience?

Many with IBS or poor gut health also complain of:

What conditions should be ruled out before a diagnosis of IBS is given?

  • Inflammatory Bowel disease (IBD)

  • Colorectal cancer

  • Colitis

  • Coeliac disease

Alarm symptoms, such as unintended weight loss, frequent watery diarrhea, anemia, and appearance of blood in stool, should trigger a clinician to consider an alternative diagnosis to IBS and investigate further. (1,37)

Symptoms that interfere with sleep, that develop after 50 years of age, that occur in those with a family history of inflammatory bowel disease, colorectal cancer and/or coeliac disease should also make the clinician more wary. (1)

What can be an underlying cause of IBS symptoms?

"60% to 70% of IBS patients report a worsening of symptoms after meals, 50% to 70% report intolerance to various foods, and more than 70% believe that foods cause their symptoms." (38)

Distension of the gut, food hypersensitivity, and direct action of the food chemicals on the gut have been proposed as mechanisms by which food items might induce symptoms. (39,40,41)

Overgrowth - bacterial or fungal

SIBO is thought to be one of the most common causes of IBS, with some indications it could be as high as a 78% incidence rate! (47)

If bloating or even reflux/heartburn is a frequent issue then SIBO should definitely be investigated.

  • Large intestinal bacterial overgrowth (LIBO) (46)

  • Candida or fungal overgrowth (Small Intestinal or large intestinal Fungal Overgrowth - SIFO or LIFO) (47,48,49)

In one small study, 26% of people with unexplained GI symptoms had an overgrowth of fungus in the small intestines (SIFO). Another study found 25.3% had SIFO.(49)

Man on toilet with irritable bowel syndrome


Emotional stress is a known trigger as it impacts greatly on gut motility (motion) and "leakiness"; enzyme, bile and stomach acid secretions; and the diversity of the gut microbiome. (50,51)

But it's typically not the only cause. (52)


A chronic infection or gut damage from a previous infection can be an underlying cause of irritable bowel symptoms, particularly for those with IBS-D or IBS-M type of IBS.

  • Past bacterial, viral or parasitic infection

Post-infectious IBS (PI-IBS) begins after an episode of acute gastroenteritis, also referred to as a "tummy bug" or food poisoning, and is most commonly due to a bacterial infection. (53,54)

According to a review of over 45 studies by the Mayo clinic, one in nine individuals who experience food poisoning can go on to develop post-infectious IBS. (55)

  • A chronic bacterial or viral infection

Campylobacter, E.coli, and Salmonella are examples of bacteria that can cause gastrointestinal symptoms.

Clostridium difficile is a species of bacteria that is frequently hospital acquired and can cause severe diarrhea, and even psychological symptoms. (56)

Specific adenoviruses, noroviruses and rotoviruses can be a common cause of gastrointestinal symptoms also. (57)

Parasites are organisms that use a host to survive and can be a cause of a range of symptoms, but gastrointestinal upset is common.

Other potential causes of IBS-like symptoms include:

What is the remedy for IBS?

While some argue that IBS can only be managed and not fully "cured," I disagree. Through my extensive experience assisting individuals in overcoming their IBS symptoms, I've found that identifying the root causes is crucial. Once these causes are pinpointed, numerous therapeutic approaches, both natural and medicinal, can be employed to address underlying issues and restore gut health for a lasting solution to IBS.

Merely managing IBS often involves imposing significant dietary restrictions, adopting a low FODMAP diet, and utilizing stress-relief techniques. While these measures can be beneficial, they typically fall short in addressing the most prevalent causes of IBS, such as bacterial or fungal overgrowth and gut damage resulting from a prior infection.

For those seeking a comprehensive, science-backed solution to alleviate abdominal pain, bloating, gas, constipation, or diarrhea, I recommend exploring the Nourish to Flourish IBS & Gut Healing Solution. In as little as a few months, individuals with IBS can reclaim their lives!

IBS can profoundly impact a person's daily life, affecting work, study, travel, relationships, and more. Those dealing with IBS should not resign themselves to a lifetime of merely managing symptoms; they deserve more—a solution that goes beyond surface-level symptom control.

Dr Georgina Compton

B.Sc, B. Chiro, CFMP, MNZCA

Certified Functional Medicine Practitioner & Chiropractor

Ready to move beyond just coping with your IBS symptoms and tackle the underlying issues for a lasting solution?

Then check out my IBS Solution online course or let's have a conversation to determine if my 1:1 IBS & Gut Healing program is the right fit for you. While I'm located in Auckland, New Zealand, I work with clients worldwide. Schedule a complimentary discovery call here.

Nourish to Flourish IBS Solution


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