Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS) is a functional gastrointestinal (GI) disorder.1 It is a collection of symptoms, including recurring abdominal pain, bloating and changes in bowel movements1,2.

What does IBS mean?

It’s easy to imagine an irritated gut, but it represents a lot more than a traditional belly cramp. IBS is defined as a chronic condition, with several symptoms that affect your large intestine (otherwise called your colon.)

What does IBS look like?

IBS occurs without any visible signs of damage or disease to the digestive tract2. This means it often has to be managed long-term.

The main job of your colon is to help you get rid of your poop! It absorbs water and nutrients from partially digested food. Whatever isn’t absorbed is slowly moved through the colon to the rectum (end part of the colon by the anus,) where it leaves your body as waste.

Muscles in the colon work to get rid of waste. They contract and relax in order to push out undigested food through. If the colon’s muscles don’t work at the right speed, or if coordination is off, movement through won’t be smooth.

When this happens, you can feel belly aches, bloating, constipation and diarrhea: all potential signs of IBS.

What are the Types of IBS?

IBS is traditionally divided into four subgroups representing the patterns of your bowel habits. The basic idea of these subgroups is to identify the main IBS symptoms in order to design a treatment that effectively meets your needs and concerns.

Based on that predominant symptom, researchers have defined them as follows3:

  • IBS with constipation (IBS-C)
  • IBS with diarrhea (IBS-D)
  • IBS with mixed-bowel habit – diarrhea and constipation (IBS-M)

How is IBS diagnosed?

IBS is defined based on symptoms. An IBS diagnosis will be made by a gastroenterologist.

Typically, a consultation will begin with a physical examination and medical history check. A doctor will ask questions to determine if there is a consistent history of symptoms that are characteristic of IBS.

Lab tests routinely ordered by doctors include a:

  • Complete blood count
  • Erythrocyte sedimentation rate test
  • Fecal occult blood tests.10

Since IBS symptoms can be similar to other diseases or disorders, there can be diagnostic errors, including celiac disease, inflammatory bowel disease, or colorectal cancer.11

Doctors use a set of symptom-based clinical guidelines to diagnose IBS. They include the Rome IV criteria.

These are based on abdominal pain, and changes in bowel habits.1 IBS diagnosis is made based on a report of bowel habits that need to have begun at least 6 months prior to diagnosis.

Other criteria that must be checked off include recurrent stomach pain for at least 1 day per week during the 3 months before diagnosis combined with at least two of the following:1

  • Pain related to a bowel movement
  • Associated changes in stool frequency
  • Associated changes in stool form/appearance

These bowel habit changes also include symptoms that are predominantly related to either diarrhea or constipation. It also includes people with a mix of bowel movements that include both loose and hard stools.1

How Common is IBS?

The global prevalence of IBS is not a straightforward answer. Diagnostic criteria to assess IBS symptoms have been regularly changing since the 1970s3.
As of today, between 3.8% – 9.2% of the global population live with IBS4.

What’s more, it’s likely these case numbers are significantly underestimated, since most IBS patients avoid the hospital. This is for a variety of reasons, such as fear of social stigma, poor health care infrastructure and a lack of opportunities to access hospitals1. Thus, a large number of people who have yet to seek medical guidance are disregarded in official figures.

Symptoms compatible with IBS…are highly prevalent in Denmark. A high proportion of sufferers are undiagnosed.5

In Denmark, IBS has been described as “a major health issue” commonly affecting the adult population3. Compared to Europe, Denmark’s IBS prevalence was 3.4% greater, with 13% of its population diagnosed in 20135.

IBS often goes undiagnosed. On average, only about 1 in 5 Danes experiencing symptoms reach out for medical advice, as reported in the Scandinavian Journal of Gastroenterology5.

How does IBS start?

IBS can make your bowel a rather polarizing personality to live with. Symptoms can start at any age but usually appear during your 20s or 30s6.
Typically, IBS begins as a dysfunction of the large intestine. The exact origins of IBS remain hazy. Different explanations may emerge, depending on who you ask. For example, some doctors may blame the food products you eat, while others could fault your mental state or physical fitness.
No wonder there are several theories that speculate on IBS causes!

How do you get IBS? Potential Causes of IBS.

Ever since it’s conceptualization in 1944, the root cause of IBS has been under debate. Many causes are thought to contribute to its development7.
The causes of IBS are not fixed in time, but rather interacting throughout your lifetime.

In other words, there could be a cocktail of causes that contribute to triggering IBS – and worsening its associated symptoms7.  This could include:

  • Genetics at infancy
  • Childhood food habits
  • Gut health as an adult

Gastroenteritis is defined as the inflammation of the mucus membranes of the gastrointestinal tract and is characterized by diarrhea or vomiting8.”

These are the most common theories on how you get IBS:

  • Demographic: Although IBS occurs in all age and sex groups, half of the patients report initial discomforts before age 35. Symptoms are generally also up to 3-times higher in groups of women compared to men3,6.
  • Socio-economic: Some studies reveal a strong correlation between IBS and socioeconomic status, theorizing IBS as ‘a disease of the industrialized world.’ The theory suggests that people with less income are at higher risk of IBS due to their lower healthcare opportunities and greater stress levels3.
  • Gut health: Other theories suggest that inflammatory diseases affecting the gut microbiota – especially lactobacillus and bifidobacteria – can exacerbate IBS symptoms9.
  • Genetics: Genetic factors seem to play a key role. People with a family member with IBS are at double risk of having the condition as well3.


  1. Schmulson MJ, Drossman DA. What Is New in Rome IV. J Neurogastroenterol Motil. 2017;23(2):151–163. doi:10.5056/jnm16214
  2. Definition & Facts for Irritable Bowel Syndrome. National Institute of Diabetes and Digestive and Kidney Diseases. Available at Accessed 4/14/20.
  3. Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clin Epidemiol. 2014;6(1):71-80. doi:10.2147/CLEP.S40245
  4. Oka P, Parr H, Barberio B, Black CJ, Savarino E V., Ford AC. Global prevalence of irritable bowel syndrome according to Rome III or IV criteria: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2020;5(10):908-917. doi:10.1016/S2468-1253(20)30217-X
  5. Krogsgaard LR, Engsbro AL, Bytzer P. The epidemiology of irritable bowel syndrome in Denmark. A population-based survey in adults ≤50 years of age. Scand J Gastroenterol. 2013;48(5):523-529. doi:10.3109/00365521.2013.775328
  6. Spiegel BMR. The burden of IBS: Looking at metrics. Curr Gastroenterol Rep. 2009;11(4):265-269. doi:10.1007/s11894-009-0039-x
  7. Marshall JK. The Origins of Irritable Bowel Syndrome: Experience of a Lifetime. Gastroenterology. 2014;147:18-20. doi:10.1053/j.gastro.2014.05.024
  8. Chow CM, Leung AKC, Hon KL. Acute gastroenteritis: From guidelines to real life. Clin Exp Gastroenterol. 2010;3(1):97-112. doi:10.2147/ceg.s6554
  9. These S, This S. 3 Causes and mechanisms. Published online 2003.
  10. Sayuk GS, Gyawali CP. Irritable bowel syndrome: modern concepts and management options. Am J Med. 2015;128:817-827.
  11. Wilkins T, Pepitone C, Alex B, Schade RR. Diagnosis and management of IBS in adults. Am Fam Physician. 2012;86:419-426.

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