What is irritable bowel syndrome (IBS)?
Irritable bowel syndrome is a functional gastrointestinal (G.I.) disorder, meaning symptoms are caused by changes in how the G.I. tract works. People with a functional G.I. disorder have frequent symptoms; however, the G.I. tract does not become damaged. IBS is a group of symptoms that occur together, not a disease. In the past, IBS was called colitis, mucous colitis, spastic colon, nervous colon, and spastic bowel. The name was changed to reflect the understanding that the disorder has both physical and mental causes and is not a product of a person’s imagination.
IBS is diagnosed when a person has had abdominal pain or discomfort at least three times a month for the last 3 months without other disease or injury that could explain the pain. The pain or discomfort of IBS may occur with a change in stool frequency or consistency or be relieved by a bowel movement.
IBS is often classified into four subtypes based on a person’s usual stool consistency. These subtypes are important because they affect the types of treatment that are most likely to improve the person’s symptoms. The four subtypes of IBS are
What causes IBS?
The causes of IBS are not well understood. Researchers believe a combination of physical and mental health problems can lead to IBS.
Brain-Gut Signal Problems
Signals between the brain and nerves of the small and large intestines, also called the gut, control how the intestines work. Problems with brain-gut signals may cause IBS symptoms, such as changes in bowel habits and pain or discomfort.
G.I. Motor Problems
Normal motility, or movement, may not be present in the colon of a person who has IBS. Slow motility can lead to constipation and fast motility can lead to diarrhea. Spasms, or sudden, strong muscle contractions that come and go, can cause abdominal pain. Some people with IBS also experience hyperreactivity—a dramatic increase in bowel contractions in response to stress or eating.
Hypersensitivity
People with IBS have a lower pain threshold for bowel stretching caused by gas or stool compared with people who do not have IBS. The brain may process pain signals from the bowel differently in people with IBS.
Mental Health Problems
Mental health problems such as panic disorder, anxiety, depression, and post-traumatic stress disorder are common in people with IBS. The link between these disorders and development of IBS is unclear. G.I. disorders, including IBS, are often found in people who have reported past physical or sexual abuse. Researchers believe people who have been abused tend to express psychological stress through physical symptoms.
Bacterial Gastroenteritis
Some people who have bacterial gastroenteritis—an infection or irritation of the stomach and intestines caused by bacteria—develop IBS. Researchers do not know why gastroenteritis leads to IBS in some people and not others, though abnormalities of the G.I. tract lining and psychological problems may be factors.
Small Intestinal Bacterial Overgrowth
Normally, few bacteria live in the small intestine. Small intestinal bacterial overgrowth is an increase in the number or a change in the type of bacteria in the small intestine. These bacteria can produce extra gas and may also cause diarrhea and weight loss. Some researchers believe that small intestinal bacterial overgrowth may lead to IBS, and some studies have shown antibiotics to be effective in treating IBS. However, more research is needed to show a link between small intestinal bacterial overgrowth and IBS.
Body Chemicals
People with IBS have altered levels of neurotransmitters—chemicals in the body that transmit nerve signals—and G.I. hormones, though the role these chemicals play in developing IBS is unclear. Younger women with IBS often have more symptoms during their menstrual periods. Post-menopausal women have fewer symptoms compared with women who are still menstruating. These findings suggest that reproductive hormones can worsen IBS problems.
Genetics
Whether IBS has a genetic cause, meaning it runs in families, is unclear. Studies have shown IBS is more common in people with family members who have a history of G.I. problems. However, the cause could be environmental or the result of heightened awareness of GI symptoms.
Food Sensitivity
Many people with IBS report that symptoms are triggered by foods rich in carbohydrates, spicy or fatty foods, coffee, and alcohol. However, people with food sensitivity typically do not have clinical signs of food allergy. Researchers have proposed that symptoms may result from poor absorption of sugars or bile acids, which help break down fats and get rid of wastes in the body.
What other conditions are associated with IBS?
People with IBS often suffer from other G.I. and non-G.I. conditions. GI conditions such as gastroesophageal reflux disease (GERD) and dyspepsia are more common in people with IBS than the general population. GERD is a condition in which stomach contents flow back up into the esophagus—the organ that connects the mouth to the stomach—because the muscle between the esophagus and the stomach is weak or relaxes when it should not. Dyspepsia, or indigestion, is upper abdominal discomfort that often occurs after eating. Dyspepsia may be accompanied by fullness, bloating, nausea, or other G.I. symptoms.
Non-GI conditions often found in people with IBS include
How does stress affect IBS?
Stress can stimulate colon spasms in people with IBS. The colon has many nerves that connect it to the brain. These nerves control the normal contractions of the colon and cause abdominal discomfort at stressful times. In people with IBS, the colon can be overly responsive to even slight conflict or stress. Stress makes the mind more aware of the sensations that arise in the colon. IBS symptoms can also increase a person’s stress level.
Some options for managing stress include:
