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What is irritable bowel syndrome?

Irritable bowel syndrome (IBS) is a chronic condition affecting the gastrointestinal (GI) tract. Symptoms can include abdominal pain – which typically improves after a bowel movement – and changes in stool frequency and form.1,2

IBS is common, affecting between 10-20% of people in the US across all ages. Many people with IBS don’t know they have it, and up to 75% never get a formal diagnosis. IBS is more common in people over 50 years old, and women are up to twice as likely as men are to get IBS.3,4,5

What are the symptoms?

The symptoms of IBS vary per patient. Patients can experience diarrhea (IBS-D), constipation (IBS-C), or a mix of both (IBS-M).1
Common symptoms of IBS include:

  • Abdominal pain, cramping or discomfort
  • Bloating
  • Constipation
  • Frequent stools
  • Gas
  • Loose stools

 What are the causes?

The exact causes of IBS are not fully understood. The condition has been linked to problems with gut motility (the movement of digested food through the gut), heightened sensitivity to gut discomfort, and psychological problems such as stress, anxiety, and depression.1,2

More recent research has suggested new links between IBS and gut inflammation, gut infections, and problems with the gut barrier, which controls the movement of nutrients and microorganisms from your gut into your bloodstream. The composition of your gut microbiome also appears to play an important role in maintaining gut barrier stability and integrity.1,6,7,8

IBS can develop in different ways. For some people, IBS seems to have a genetic or inflammatory component. When triggered by environmental factors like a high-fat diet, gut microbiota-derived lipopolysaccharides (LPS), drugs such as non-steroidal anti-inflammatory drugs (NSAIDs), or the use of proton pump inhibitors (PPIs), a person’s genes may influence a breakdown in the efficacy of their gut barrier, leading to inflammation.9 This inflammation, combined with stress or anxiety, may disrupt the gut microbiome and increase the risk of infection.1,10 This may then lead to changes in how digested food moves through the gut, resulting in symptoms of IBS.1,10,11

For others, IBS seems to be more of a gut-brain disorder, involving both the gut and the central nervous system.1,10,11,12 Gut infections,13 inflammation10, certain foods8,14, and medications15 may lead to changes in the gut microbiome and how it functions. This can trigger changes in the central nervous system, which may influence the development of anxiety, depression, and related problems. These, in turn, can contribute to the start of IBS symptoms, or make them worse.1,10,11 These differences are subtle, but exploring them may help researchers discover better ways to treat IBS.

Gut motility corresponds to the stretching and contracting movement of the muscles throughout the gastrointestinal tract. These muscle contractions are needed to move the food from the stomach down to the rectum. Gut motility is related to the frequency of bowel movements. If gut motility activity is too low, we are constipated. If motility is too high, we have diarrhea.25
The gut barrier is the physical and functional layer forming the lining of the gastrointestinal tract (mainly the intestines). In a healthy gut, this barrier forms a tight shield between the bacteria and food in our intestinal tract, and our own human cells. Despite this tight lining, the cells lining the gut can selectively secrete enzymes to digest our food and take up digested small molecules from our food. If the gut barrier is disrupted, there is space between these intestinal cells, allowing contact between food components and gut microbes and our own cells. A disrupted gut barrier is associated with inflammation of the gut, and has been found in several diseases, such as inflammatory bowel disease and celiac disease.26
The gut microbiome includes all the genes and functions represented by the microbial communities living in the gut.27
LPS can be found in the external layers of several bacterial species, and are often associated with pathogenic effects in pathogenic organisms. LPS are powerful stimulators of the immune response, causing inflammation.28

How does this topic relate to my microbiome?

Your microbiome can become imbalanced if the balance or composition of microbes in your gut are disrupted. This “dysbiosis” has been linked to a variety of health problems, including IBS.7,15,16,17

Other evidence supports the role of the gut microbiome in IBS. For example, studies have that people might develop IBS after GI tract infections caused by bacteria such as Campylobacter and Salmonella.2,6,18,19 Research has also linked improvements in IBS symptoms with the use of prebiotics and probiotics, which can help restore the gut’s microbial balance.2,11,17

Which diseases/topics are related to this particular disease/topic?

IBS is a condition that affects the normal function of the GI tract. There are several other conditions or diseases whose symptoms can affect the GI tract. These include:

  • Diarrhea
  • Crohn’s disease
  • Inflammatory bowel disease
  • Ulcerative colitis

IBS can also occur alongside other conditions, including:

  • Anxiety17,20
  • Chronic fatigue syndrome
  • Chronic pelvic pain
  • Dyspepsia (indigestion)3,21
  • Fibromyalgia
  • Gastroesophageal reflux3,22
  • Major depression17,20
  • Reduced health-related quality of life1,3,23
  • Somatization24

Somatization refers to psychological distress linked to physical symptoms.

How can I take action?

First, consult your healthcare provider. The selection of specific tests and treatments depends on your symptoms, whether you have IBS with diarrhea, constipation, or a mix of both. To rule out inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis, a doctor might order an endoscopy or colonoscopy for an accurate diagnosis.

During these procedures, a doctor will insert a long tube with a camera either through the mouth (endoscopy) or the rectum (colonoscopy) to take a look inside the intestinal tract. A healthy gut will look smooth and pink, while an inflamed gut will show red patches or areas, and may easily bleed. If the gut does not look inflamed, the patient is not likely to have IBD, but might have IBS.

There are several treatments that can help improve symptoms of IBS. These may include making changes to your diet or lifestyle, taking medications, or talk therapies like behavioral therapy or relaxation training.

Below is a list of possible treatments, and the IBS signs and symptoms they can improve. Please consult your health provider to determine which options are right for you.1

  • Antibiotics (infections, bacterial overgrowth in the small intestine)
  • Antidepressants (gut pain, psychological distress)
  • Anti-diarrheal treatments (diarrhea)
  • Antispasmodics (abdominal cramps, diarrhea)
  • Cognitive behavioral therapy (overall symptoms)
  • Diet changes (overall symptoms)
  • Exercise (overall symptoms)
  • Fiber (constipation)
  • Intervention treatments (psychological distress)
  • Laxatives (constipation)
  • Prebiotics (bloating, gas)
  • Probiotics (bloating, gas)
  • Serotonin agents (gut discomfort)


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