What Is Irritable Bowel Syndrome (IBS)?

Irritable bowel syndrome (IBS) is a debilitating condition that affects more than one in ten people. BS is a functional intestinal disorder characterized by chronic abdominal pain and changes in bowel patterns. IBS has no specific organic cause and no abnormalities that show up on endoscopies, blood tests or radiologic studies (x-rays).

IBS is identified in patients when they have had recurring abdominal pain or discomfort at least three days a month for at least three months and when:

  • the problem improves with defecation, or
  • the onset of symptoms is associated with a change in the frequency or form of stool

There are four basic forms of IBS:

  • constipation-predominant irritable bowel syndrome (IBS-C)
  • diarrhea-predominant irritable bowel syndrome (IBS-D)
  • mixed irritable bowel syndrome (IBS-M), in which both constipation and diarrhea can be a problem
  • unclassified irritable bowel syndrome (IBS-U), in which patients may exhibit a variety of symptoms

Although IBS shares some characteristics with inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis, it should not be confused with these or other gastro-intestinal conditions. There is, however, some association with these other diseases; about one-third of patients with ulcerative colitis and just over two-fifths of patients with Crohn’s disease also have IBS.

What Are the Causes of IBS?

IBS is caused by a central dysregulation -- miscommunication between the brain and the gut. This flawed connection results in a heightened sensitivity to everyday intestinal functions: gas and the colonic motor activity and contractions that allows a body to eliminate stool. The brain-gut disconnect common to IBS patients makes these otherwise normal functions bothersome and painful.

Some of the conditions that may lead to IBS are:

  • Abnormal intestinal motility – an inability of the intestines to contract and propel digested food normally
  • Visceral hypersensitivity – heightened sensitivity of the intestines to normal sensations
  • Low-grade inflammation – caused by infections, altered gut flora, bile, or food
  • Genetics
  • Psychological and psychiatric factors including stress, depression, anxiety and somatization

Food triggers may also play a part in IBS, including:

  • Gluten intolerance in some IBS patients who do not have overt celiac disease
  • Fructose and sorbitol malabsorption
  • Reactions to other foods

What Are the Symptoms of IBS?

IBS patients may suffer from a combination of intestinal and non-intestinal symptoms.


  • Constipation
  • Diarrhea
  • Bloating
  • Nausea
  • Epigastric pain – pain in the upper abdomen immediately below the ribs

Non-Intestinal (or Extra-Intestinal)

  • Headache
  • Backache
  • Trouble sleeping
  • Chronic fatigue
  • Pelvic pain
  • Mood changes

These non-intestinal symptoms can be signs of a wide variety of conditions, but when associated with any of the intestinal symptoms listed, they can be signs of IBS.

How Is IBS Diagnosed?

Because IBS has no tangible abnormalities that can be detected with traditional imaging and testing, successful diagnosis depends on assessment by an experienced gastroenterologist who understands the complex interaction of the condition’s symptoms and their underlying causes.

Patients should be screened for IBS if they have a history of:

  • Blood in the stool
  • Family history of colon cancer, IBD or celiac disease
  • Fever
  • Night-time symptoms
  • Chronic diarrhea
  • Progressive dysphagia – an inability to swallow properly
  • Recurrent vomiting
  • Severe chronic constipation
  • Travel to areas endemic for infections
  • Weight loss

Patients should be screened for IBS if a physical examination reveals:

  • Abdominal mass
  • Arthritis
  • Dermatitis herpetiformis or pyoderma gangrenosum
  • Blood during rectal exam
  • Signs of:
    • Anemia
    • Intestinal obstruction
    • Intestinal malabsorption
    • Thyroid dysfunction

How Is IBS Treated?

A number of different therapies are available to help IBS patients control their symptoms and maintain a normal, healthy lifestyle. They include:

  • Dietary changes -- including diets low in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). Dietary plans should be established with the guidance of a gastroenterologist and nutritionist.
  • Interventions that modify the microbiota – probiotics or antibiotics
  • Antispasmodics
  • Peppermint oil
  • Loperamide
  • Antidepressants
  • Serotonergic agents
  • Prosecretory agents
  • Psychological therapy

Watch this informational presentation to learn more about irritable bowel syndrome.

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