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Irritable bowel syndrome (IBS)


@Dragana Gordic at Freepik


Posted: 24/06/2018

Updated: 15/07/2018

Irritable bowel syndrome, also known as IBS is one of the most common, long-term disorder that affects the digestive system (1). IBS describes a pattern of recurrent bouts of abdominal pain and abnormal bowel motility commonly causing diarrhoea, constipation, flatulence and bloating in the absence of an overtly identifiable cause. This could be a major burden in the quality of life, work productivity and healthcare costs.

IBS is different from inflammatory bowel syndrome (IBD), which involves some similar symptoms but also contains inflammation, ulcers and other damage to the bowel, whereas IBS does not involve these, and instead can be thought of a functional disorder.


A functional disorder refers to the presence of symptoms but the performance of physical examinations like endoscopy or blood tests will not show any physical problems.

  • Abdominal pain or/and discomfort

  • Bloating

  • Change of bowel habit (interludes of diarrhoea or constipation or both mixed/alternating)

main Symptoms

Symptoms vary between individuals and can affect other parts of the body (2).​​

  • ​​Sexual dysfunction

  • Halitosis (Bad breath)

  • Dysmenorrhoea/Irregular menses

  • Frequent urination

  • Fibromyalgia symptoms (widespread body, increased sensitivity to pain, persistent fatigue)



IBS is also classified into different subtypes based on the person’s stool characteristics (3):​​


Bristol types 1 & 2

hard or lumpy stools >25%

loose or watery stools <25%



Bristol type 6

hard or lumpy stools <25%

loose or watery stools >25%



hard or lumpy stools <25%

loose or watery stools <25%



Bristol types 1 & 6

hard or lumpy stools >25%

loose or watery stools >25%




As IBS is a functional disease, tests such as sigmoidoscopy, colonoscopy, stool cultures and blood tests prove negative for any pathologic bowel change. However, these tests are useful for the exclusion of organic disease.

The diagnosis of IBS is usually made from the symptoms experienced.


The definition of IBS has been evolving and the most recent Rome IV criteria were released in 2016.


Previously, the gold-standard for the diagnosis of IBS is the Rome Criteria III published in 2006 which states (4):

Rome Criteria III

That a patient must have recurrent abdominal pain or discomfort at least 3 days/month in the last 3 months associated with two or more of the following (5):

  • Improvements with defecation

  • Onset associated with a change in frequency of stool

  • Onset associated with a change in form (appearance) of stool

Rome IV Criteria

Recurrent abdominal pain, on average, at least 1 day/week in the last 3 months, associated with two or more of the following criteria:​

  • Related to defecation

  • Associated with a change in frequency of stool

  • Associated with a change in form (appearance) of stool

Criteria fulfilled for the last 3 months with symptom onset at least 6 months before diagnosis.

In addition, psychological factors and dietary habits are also used as screening tools for IBS.



The prevalence varies according to country depending on the criteria used to define IBS. It is one of the most common gastrointestinal disorders and accounts for about one-third of the visits to see a gastroenterologist (6).


Prevalence of IBS in each country here.

Adapted from Enck P et al., 2016 (7)

The prevalence of IBS in Europe and North America is estimated to be 10–15% (8).


However, this may be underestimated as many people with IBS tend not to seek medical attention and is underdiagnosed (9).


Globally, Southeast Asia has the lowest prevalence of IBS (7.0%) and South America the highest (21.0%).


IBS is most common between 20 to 40 years of age with a significant female predominance (10).


In most countries, prevalence rates in women are 1.5 – 3-fold higher than those seen in men (11).

causes and triggers

Possible causes and triggers

Although the underlying pathophysiology is not well understood, several theories have been speculated.


Theories include combinations of the gut-brain axis problems, gut motility disorders, pain sensitivity, infections including small intestinal bacterial overgrowth (SIBO), neurotransmitters, genetic factors, and food sensitivity (12).

Environmental Factors

  • Psychosocial issues

  • Food

  • Medication

  • Supplements

  • Antibiotics

  • Enteric infection

Host Factors

  • Altered gastrointestinal motility

  • Visceral hypersensitivity

  • Altered brain-gut interactions

  • Increased intestinal permeability

  • Gut mucosal immune activation

Luminal Factors

  • Dysbiosis

  • Neuroendocrine mediators

  • Bile acids

Overview of IBS pathophysiology (13).

Visceral hypersensitivity


Approximately 30 to 40 per cent of patients with IBS are reported to have visceral hypersensitivity (14).


This means that the sensory nerve endings in the intestinal walls are overactive to stimuli like colonic distension during and after a meal. The may explain why patients experience recurrent bouts of abdominal pain and discomfort.


Visceral hypersensitivity not only occurs in people with IBS but also in those with: functional dyspepsia, non-cardiac chest pain and functional abdominal pain.

Bacterial overgrowth


Those with small intestinal bacterial overgrowth (SIBO) may also experience abdominal pain or discomfort, bloating, flatulence and loose motion.

This is characterised by abnormally high bacteria counts in the small intestine (15). Bacterial overgrowth in the small intestine can interfere with digestion and absorption of nutrients. Bacterial fermentation occurs producing hydrogen, methane and carbon dioxide gases which contributes to IBS symptoms.

Between 4 and 78 per cent of patients with IBS are known to have SIBO (16). The variation can be attributed to the difference in studied population and the criteria used for the diagnosis.


SIBO is more often associated with diarrhoea than constipation-predominant IBS (17).

Gastrointestinal Infection

Studies have shown a strong association between acute enteric infection and subsequent IBS symptoms (18, 19).


This is termed as post-infectious IBS (IBS-PI) develops in 4 to 32 per cent of patients with bacterial gastroenteritis (20). As the name suggests, this type of IBS develops after an infection in the stomach and intestines. While most people recover completely from gastroenteritis, some do not.


This can be caused by a variety of enteric pathogens such as Campylobacter, Salmonella, diarrheagenic strains of Escherichia coli and Shigella species (21). Bacterial infections are typically contracted by consuming contaminated food or water or contact with infected people.

Brain-gut interaction

The brain-gut axis (BGA) is the bidirectional interaction via the vagus nerve between the digestive tract (enteric nervous system ENS) and the brain (central nervous system CNS) (22).

There is a large number of nerve cells in the gut and sometimes is referred to as the “second brain”. This connection is how stress, emotion and psychological problems can affect gut sensation, motility and secretion.

Likewise, sensations arising in the gut can affect the brain leading to discomfort, pain or changes in mood and behaviour (23).

Of 50 to 90 per cent of IBS patients have psychiatric comorbidities including anxiety and depression (24). However, the relationship between this is not clearly understood.

When the brain-gut axis (BGA) is in balance, our brain function and digestive system function optimally. However, structural and functional disruptions in the brain-gut axis (BGA) can result in IBS symptoms (25).

Food intolerance

Eating foods that contain FODMAPs (Fermentable, Oligo-, Di-, Mono-saccharides, And Polyols") which are short-chain carbohydrates often can trigger the symptoms. Examples include:


  • fructose (fructans)

  • galactooligosaccharides (GOS)

  • disaccharides (fructans)

  • monosaccharides (fructose)

  • sugar alcohols (polyols like sorbitol, mannitol, xylitol and maltitol)


FODMAPs are poorly absorbed and malabsorption leads to causes unabsorbed short-chain carbohydrates to act as solutes that draw water across the gastrointestinal wall and into the lumen. Excess water can cause the smooth muscle lining to spasm and create diarrhoea contributing to IBS symptoms.


In addition, short-chain carbohydrates are fermented by colonic bacteria which results in the production of short-chain fatty acids, hydrogen, carbon dioxide and trace gases that trigger more bloating, abdominal distension, abdominal pain or discomfort (26).



Although IBS is not dangerous, it can still be very painful and bothersome. Fortunately, many people can find out what makes them feel better and what makes them feel worse (27).


As the underlying biological mechanisms that produce the symptoms of IBS aren’t well understood, treatment is focused on the key symptoms, such as constipation, diarrhoea and mixed presentation of both.



Medical management has been focused on the symptomatic treatment of individual complaints. Drug therapies are administered based on the predominant symptoms and IBS-subtype.


  • Fibre

  • Laxatives

  • Antidepressants

  • Prosecretary agents

  • Chloride channel activators

  • Opioid antagonists

  • Serotonin receptor 3 and 4 agonists




  • Antidiarrheals

  • Antidepressants

  • Antibiotics

  • Serotonin receptor 3 and 4 antagonists

  • Alpha-receptor agonists



  • Antibiotics

  • Probiotics

  • Antispasmodics

The medication loperamide may be used to help with diarrhoea while laxatives may be used to help with constipation.


In addition, to treat constipation, soluble fibre, stool softeners and osmotic laxatives can help, whereas, for gastrointestinal spasms and pain, antidiarrheals like serotonin antagonists and antimuscarinic medications can help.


Psychiatric treatment can help alleviate anxiety and depression that accompanies IBS. This includes the use of antidepressants or anxiolytics, psychotherapy and focusing on psychosocial stressors. Psychiatric treatments have demonstrated effectiveness in reducing IBS symptoms and improvement of patient functioning (28).


Always check with your practitioner before going on any medications.

Drug Class

Possible Side Effects


  • Loperamide

  • Diphenoxylate/Atropin


  • Imipramine

  • Amitriptyline


  • Rifaximin

Serotonin receptor 3 antagonist

  • Alosetron

  • Cilansetron


  • Peppermint oil

  • Dicyclomine

  • Hydrochloride

  • Hyoscyamine sulphate

exacerbate constipation, blurred vision, vomiting, diarrhoea, nausea

exacerbate GI symptoms

headache, rectal tenesmus, abdominal pain ​​

ischemic colitis with alosetron, constipation


Adapted from Ikechi et al., 2017 (29).

Holistic Approaches

holistic approaches

Modulation with dietary changes, prebiotics/probiotics and stress reduction techniques offers holistic means of treating IBS.



FODMAPs (2nd line approach)

Diet modification such as the low-FODMAP diet includes avoiding certain foods like apples, beans, and cauliflower, all of which have short-chain carbohydrates.


Adopting this highly restrictive diet may improve digestive symptoms in the short term but can be detrimental to the microbiome in the long term (30).


Implementing such diet can be challenging and carries a risk for nutritional deficiencies. Dietitians can help counsel patients on the various aspects of the low-FODMAP diet.



Those with the constipation subtype IBS-C may benefit from a high soluble fibre diet found in barley, oats, rye and legumes (31).

Fibre can make it easier to have a bowel movement because the fibre will brush up against the bowel lumen which helps secretes a mucous to help it get through. It can also absorb fluid in the bowel to relieve constipation and diarrhoea.


Remember to increase your intake of fibre slowly to avoid worsening of symptoms.


On the other hand, insoluble fibre like whole grains, wheat bran, legumes, nuts, seeds, fruits and non-starchy carbohydrates has not been found effective in reducing symptoms of IBS and in some cases exacerbates symptoms (32).



Gluten is a protein found in barley, rye and wheat that can cause damage to the intestine in people with gluten-sensitivity/intolerance or in extreme cases coeliac disease. 


A gluten-free diet may improve gastrointestinal problems. Foods that include gluten include cereals, grains, pasta and many other processed foods.


In one study, gluten increases intestinal permeability also known as a leaky gut in patients with IBS-D. In this condition, the lining of the intestines is damaged allowing food particles to pass through the bloodstream causing inflammation throughout the body. By adapting to a gluten-free diet, it can actually act as a reversible mechanism for IBS (33).

Prebiotics and probiotics


Consuming probiotics and prebiotics whether from supplements or foods can improve our gut microbial balance.


Probiotics such as Lactobacilli and Bifidobacteria are beneficial bacteria while prebiotics is the food source that can selectively increase the numbers of these bacteria.


Different species, strains and doses of probiotics are sold in supplements and foods such as yoghurts in milk and the effectiveness of each for IBS remains unclear (34).


Additionally, some of these prebiotic foods such as asparagus and onions may actually be in high in FODMAPs so always check before adding them to your diet.


Few studies have been done and the results are mixed. Studies have shown that synbiotics which are a combination of both prebiotics and probiotics or a probiotic mixture VSL#3 significantly improved symptoms such as abdominal pain, bloating and constipation when administered (35, 36, 37).


However, in another study, it had shown that prebiotics was ineffective and potentially be dangerous at high levels for treating IBS (38).

Peppermint oil

Peppermint oil is a natural anti-spasmodic meaning that it acts to relax smooth muscles in the gut. In one meta-analysis, it was found to be effective in improving IBS symptoms and abdominal pain (39).​

Peppermint oil comes from the stems, leaves and flower of the peppermint plant. Peppermint tea made from the leaves of the plant are not as effective as peppermint oil capsules (40).


However, like all herbal remedies, there are possible adverse effects like heartburn and burning sensation around the anus (41). Fortunately, these symptoms are mild and transient in nature (42).

Other Remedies

According to IFFGD (the International Foundation for Functional Gastrointestinal Disorders), foods most likely to cause problems are insoluble fibre, coffee/caffeine, chocolate and nuts (43).​

Caffeine can stimulate activity in the colon and can be found in many food and beverages such as coffee (even in decaf coffee), soft drinks, teas, dark chocolate, ice cream, energy water. Patients may benefit from eliminating these foods for 12 weeks to see if symptoms improve.


Remember that everyone responds differently to different diets and always talk to a professional before going on a new diet. Record how your body reacts to different diets and hopefully, you’ll find what works best for you.



Finally, managing things like stress and controlling feelings of anxiety and depression can all help symptoms of IBS. Psychological interventions such as cognitive behavioural therapy and exercising can improve IBS symptoms (44).

  • Relaxation therapies like mindfulness, meditation

  • Exercise

  • Sleep

  • Support and counselling

Take home message

  • References
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Although IBS is not life-threatening, and it doesn’t make you more likely to get other colon conditions like colon cancer, it can still be a long-lasting problem for you that changes how you are going to live your life.

Some people with IBS miss work or school more often, and they may feel less able to take part in daily activities – some might even change their work setting like shifting to working at home or stop working at all, while other people will experience feelings of depression and anxiety.

That’s why you should take care of this disease. There is no cure for IBS, but the symptoms can in most situations be managed by making changes to your diet and lifestyle in combination with medication.

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