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What Is Irritable Bowel Syndrome (IBS)?

By William Salt, M.D. ; Updated August 14, 2017

Irritable Bowel Syndrome (IBS) is the most common gastrointestinal (GI) tract, or “gut,” diagnosis, affecting roughly one in five people worldwide and between 30 to 45 million in the United States. IBS is a functional symptom-based diagnosis, including chronic and recurring abdominal pain and/or discomfort associated with changes in bowel habits (constipation, diarrhea or both). Abdominal bloating and distention are commonly present. Classification of IBS subtypes based upon bowel function informs both testing and treatment.

IBS can significantly reduce quality of life and ability to work. Most people who would be diagnosed with IBS do not consult with a health care professional. There are many current advancements in the understanding, recognition, diagnosis and treatment of IBS.

IBS: A Functional Disorder

IBS is the most common of many functional GI disorders, or FGIDs, in which symptoms are related to dysfunction or disturbance of how the GI tract (gut) works and functions. Many patients with IBS have more than one FGID. In most cases there are no abnormalities identified by endoscopy/colonoscopy, X-ray or blood tests that account for symptoms.

IBS Symptoms and Subtypes

IBS is categorized into subtypes based upon the predominant bowel symptom(s): IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), IBS with mixed or alternating constipation and diarrhea (IBS-M) and IBS post-infectious (IBS-PI). Most patients with IBS also have abdominal tightness or fullness, called bloating. This symptom is commonly associated with abdominal enlargement, or distention.


IBS is a symptom-based diagnosis, which can be facilitated with a new app called the MyGIHealth Mobile App. IBS subgroup recognition guides and informs the diagnostic process. Diseases that can mimic IBS are considered through the patient and family history and by simple blood and stool testing. Scopes and X-rays are usually not necessary unless the history and/or basic testing raise concerns.


Management of IBS is also based upon the IBS subtype, and both patient education and healthy lifestyle (including diet, exercise, adequate sleep and stress management) serve as the foundation. Multiple potentially effective treatment options are now available. Associated anxiety and/or depression may require treatment.

Associated Conditions

IBS is often associated with other FGIDs, such as functional heartburn or upper abdominal (epigastric) pain not responsive to strong acid-reducing drugs. IBS is also commonly associated with other non-GI pain-related disorders, such as chronic headaches and fibromyalgia. Anxiety and depression are more common in IBS patients and affect illness experience.

Small Intestinal Bacterial Overgrowth Syndrome (SIBO)

Many patients with IBS have alterations in the gut microbiome, which refers to the resident bacteria and flora playing an important role in both GI and overall health. Such microbiome dysfunction is termed, “small intestinal bacterial overgrowth (SIBO).”


IBS is a chronic and relapsing disease for most, although the number of people with IBS appears to decline with age. People can change subtype over time, most commonly from IBS-C or IBS-D to IBS-M. Some of this change may be related to IBS treatments, such as the use of laxatives and antidiarrheal remedies. About two-thirds of those who develop IBS-PI following food poisoning (bacterial gastroenteritis) will recover within five years.

IBS in America Survey

The American Gastroenterological Association (AGA) in December 2015 published the most comprehensive survey of both patients and physicians ever conducted: the IBS in America survey. The survey shows that IBS symptoms are often so bothersome and unpredictable that they interfere with daily life at home, work and school, and many people suffer for years before seeing a doctor. The AGA suggests that patients speak openly and frequently with their doctors in order to receive the best possible care.

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