From the nation’s leading law firm representing victims of IBS and other foodborne illness outbreaks.

Chapter 1

About Irritable Bowel Syndrome

What is Irritable Bowel Syndrome (IBS)?

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract. The hallmark symptoms of IBS are abdominal pain and altered bowel habits.

Rome Foundation Definition

The Rome Foundation is a widely accepted independent organization that focuses on the critical appraisal of scientific inquiry into gastrointestinal function and dysfunction. It is named after the foundation’s consensus conference, which is held in Rome every decade. Functional gastrointestinal disorders (FGIDs) are diagnosed and classified using the Rome criteria; the criteria may change over time as new scientific data emerge. The Rome IV was released in May 2016. At this time, the term “discomfort” was removed from IBS criteria and the existence of functional bowel disorders was listed on a spectrum of symptom presentations, according to the degree of pain or the consistency of stool. When there is little or no pain, patients may have functional diarrhea or constipation but, in patients with greater degrees of pain, they are classified as having IBS, C or D respectively. This is based on evidence that patients often migrate across categories over time.

The Rome III classification for IBS subtypes required that the proportion of total stools using the Bristol Stool Form Scale be used to classify IBS with predominant diarrhea (>25% loose/watery, <25% hard/lumpy), IBS with predominant constipation (>25% hard/lumpy, <25% loose/watery), mixed-type IBS (>25% loose/watery, >25% hard/lumpy), and IBS unclassified (<25% loose/watery, <25% hard/lumpy). However, because patients can have large periods of time with normal stool consistency, a majority of them have unclassified IBS subtype relative to the other groups. (See chart and illustration below.)

Based on this observation and the results of a Rome Foundation Normative Symptom Study, the criteria have been changed and relate to the proportion of days with symptomatic stools (i.e., loose/watery and hard/lumpy) rather than all stools (including normal ones). As a result, the unclassified group is reduced markedly.

Rome IV Definition of IBS

Recurrent abdominal pain is a nonspecific term, has different meanings in different languages, and is ambiguous to patients. In IBS, it occurs on average at least 1 day/week in the last 3 months, and is associated with two or more of the following (criterion fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis):

  1. Can increase related to defecation; and/or
  2. Associated with change in frequency of stool; and/or
  3. Associated with change in form (appearance of stool).


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Symptoms of IBS

Abdominal pain is usually crampy in nature, but character and sites can vary. In some patients, the pain is relieved by defecation but, in others, defecation may worsen the pain. Additional symptoms may include bloating, straining at stools, and a sense of incomplete evacuation.

Altered bowel habits range from constipation to diarrhea, or alternating diarrhea and constipation.

The symptoms of IBS may be daily but, more frequently, are episodic. Symptoms may be triggered by specific foods or by stress. Often, however, no specific triggers can be identified.

It is estimated that 10-15% of the Western population has symptoms consistent with IBS, although most (75-80%) never seek medical care. IBS symptoms do account for about 10% of visits to primary care providers and for 25-30% of referrals to gastroenterologists. IBS has a significant effect on quality of life for affected individuals. IBS is 3 or 4 times more common in women than men.

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Next Chapter

Causes of IBS

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