Irritable Bowel Syndrome National Digestive Diseases Information Clearinghouse What is irritable bowel IBS is often classified into four subtypes based on a person’s usual stool consistency. syndrome (IBS)? These subtypes are important because they Irritable bowel syndrome is a functional affect the types of treatment that are most U.S. Department gastrointestinal (GI) disorder, meaning it likely to improve the person’s symptoms. of Health and is a problem caused by changes in how the The four subtypes of IBS are Human Services GI tract works. People with a functional GI disorder have frequent symptoms, but the • IBS with constipation (IBS-C) NATIONAL INSTITUTES GI tract does not become damaged. IBS is – hard or lumpy stools at least 25 per- OF HEALTH not a disease; it is a group of symptoms that cent of the time occur together. The most common symp- toms of IBS are abdominal pain or discom- – loose or watery stools less than fort, often reported as cramping, along with 25 percent of the time diarrhea, constipation, or both. In the past, • IBS with diarrhea (IBS-D) IBS was called colitis, mucous colitis, spas- – loose or watery stools at least tic colon, nervous colon, and spastic bowel. 25 percent of the time The name was changed to reflect the under- standing that the disorder has both physical – hard or lumpy stools less than and mental causes and is not a product of a 25 percent of the time person’s imagination. • Mixed IBS (IBS-M) IBS is diagnosed when a person has abdomi- – hard or lumpy stools at least 25 per- nal pain or discomfort at least three times cent of the time per month for the last 3 months without other disease or injury that could explain the – loose or watery stools at least pain. The pain or discomfort of IBS may 25 percent of the time occur with a change in stool frequency or • Unsubtyped IBS (IBS-U) consistency or may be relieved by a bowel movement. – hard or lumpy stools less than 25 percent of the time – loose or watery stools less than 25 percent of the time What is the GI tract? The large intestine absorbs water and any remaining nutrients from partially digested The GI tract is a series of hollow organs food passed from the small intestine. The joined in a long, twisting tube from the large intestine then changes waste from mouth to the anus. The movement of mus- liquid to a solid matter called stool. Stool cles in the GI tract, along with the release passes from the colon to the rectum. The of hormones and enzymes, allows for the rectum is located between the last part of digestion of food. Organs that make up the the colon—called the sigmoid colon—and GI tract are the mouth, esophagus, stom- the anus. The rectum stores stool prior to ach, small intestine, large intestine—which a bowel movement. During a bowel move- includes the appendix, cecum, colon, and ment, stool moves from the rectum to the rectum—and anus. The intestines are some- anus, the opening through which stool leaves times called the bowel. The last part of the the body. GI tract—called the lower GI tract—consists of the large intestine and anus. Transverse colon Ascending Descending colon colon Sigmoid colon Cecum Anus Rectum The lower GI tract 2 Irritable Bowel Syndrome How common is IBS and • feeling that a bowel movement is who is affected? incomplete Irritable bowel syndrome is estimated to • passing mucus, a clear liquid made by affect 3 to 20 percent of the population, with the intestines that coats and protects most studies ranging from 10 to 15 percent.1 tissues in the GI tract However, less than one-third of people with • abdominal bloating the condition see a health care provider for Symptoms may often occur after eating a diagnosis.2 IBS affects about twice as many meal. To meet the definition of IBS, symp- women as men and is most often found in toms must occur at least 3 days a month. people younger than 45 years.1 What are the symptoms of What causes IBS? The causes of IBS are not well understood. IBS? Researchers believe a combination of physi- The symptoms of IBS include abdominal cal and mental health problems can lead to pain or discomfort and changes in bowel IBS. The possible causes of IBS include the habits. To meet the definition of IBS, the following: pain or discomfort should be associated with two of the following three symptoms: • Brain-gut signal problems. Signals between the brain and nerves of the • start with bowel movements that occur small and large intestines, also called more or less often than usual the gut, control how the intestines work. • start with stool that appears looser and Problems with brain-gut signals may more watery or harder and more lumpy cause IBS symptoms, such as changes in than usual bowel habits and pain or discomfort. • improve with a bowel movement • GI motor problems. Normal motil- ity, or movement, may not be present Other symptoms of IBS may include in the colon of a person who has IBS. • diarrhea—having loose, watery stools Slow motility can lead to constipation three or more times a day and feeling and fast motility can lead to diarrhea. urgency to have a bowel movement Spasms, or sudden strong muscle con- tractions that come and go, can cause • constipation—having hard, dry stools; abdominal pain. Some people with IBS three or fewer bowel movements in also experience hyperreactivity, which a week; or straining to have a bowel is an excessive increase in contractions movement of the bowel in response to stress or eating. 1Grundmann O, Yoon SL. Irritable bowel syndrome: epidemiology, diagnosis, and treatment: an update for health-care practitioners. Journal of Gastroenterology and Hepatology. 2010;25:691–699. 2Owyang C. Irritable bowel syndrome. In: Yamada T, ed. Textbook of Gastroenterology. 5th ed. Vol. 1. West Sussex, UK: John Wiley & Sons Ltd.; 2009: 1536–1573. 3 Irritable Bowel Syndrome • Hypersensitivity. People with IBS have studies have shown antibiotics to be a lower pain threshold to stretching of effective in treating IBS. However, the the bowel caused by gas or stool com- studies were weak and more research pared with people who do not have IBS. is needed to show a link between SIBO The brain may process pain signals from and IBS. the bowel differently in people with IBS. • Body chemicals. People with IBS have • Mental health problems. Mental altered levels of neurotransmitters, health, or psychological, problems such which are chemicals in the body that as panic disorder, anxiety, depression, transmit nerve signals, and GI hor- and post-traumatic stress disorder are mones, though the role these chemi- common in people with IBS. The link cals play in developing IBS is unclear. between these disorders and develop- Younger women with IBS often have ment of IBS is unclear. GI disorders, more symptoms during their menstrual including IBS, are often found in people periods. Post-menopausal women have who have reported past physical or sex- fewer symptoms compared with women ual abuse. Researchers believe people who are still menstruating. These find- who have been abused tend to express ings suggest that reproductive hormones psychological stress through physical can worsen IBS problems. symptoms. • Genetics. Whether IBS has a genetic • Bacterial gastroenteritis. Some people cause, meaning it runs in families, is who have bacterial gastroenteritis—an unclear. Studies have shown that IBS infection or irritation of the stomach is more common in people with fam- and intestines caused by bacteria— ily members who have a history of GI develop IBS. Researchers do not know problems. However, the cause could be why gastroenteritis leads to IBS in some environmental or the result of height- people and not others, though psycho- ened awareness of GI symptoms. logical problems and abnormalities of • Food sensitivity. Many people with IBS the lining of the GI tract may be factors. report that certain foods and bever- • Small intestinal bacterial overgrowth ages can cause symptoms, such as foods (SIBO). Normally, few bacteria live in rich in carbohydrates, spicy or fatty the small intestine. SIBO is an increase foods, coffee, and alcohol. However, in the number of bacteria or a change in people with food sensitivity typically do the type of bacteria in the small intes- not have clinical signs of food allergy. tine. These bacteria can produce excess Researchers have proposed that symp- gas and may also cause diarrhea and toms may result from poor absorption weight loss. Some researchers believe of sugars or bile acids, which help break that SIBO may lead to IBS, and some down fats and get rid of wastes in the body. 4 Irritable Bowel Syndrome How is IBS diagnosed? Stool tests. A stool test is the analysis of a sample of stool. The health care provider To diagnose IBS, a health care provider will will give the person a container for catching conduct a physical exam and take a complete and storing the stool. The sample is returned medical history. The medical history will to the health care provider or a commercial include questions about symptoms, family facility and sent to a lab for analysis. The history of GI disorders, recent infections, health care provider may also do a rectal medications, and stressful events related to exam, sometimes during the physical exam, the onset of symptoms. For IBS to be diag- to check for blood in the stool. Stool tests nosed, the symptoms must have started at can show the presence of parasites or blood.