Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic, relapsing and often life-long disorder:

• characterised by the presence of abdominal pain or discomfort, which may be associated with defaecation and/or accompanied by a change in bowel habit
• symptoms may include disordered defaecation (constipation or diarrhoea or both) and abdominal distension, usually referred to as bloating
• symptoms sometimes overlap with other gastrointestinal disorders such as non-ulcer dyspepsia or coeliac disease

The cause is not known; an organic trigger, such as bacterial gastroenteritis, is seen in some patients however there is undoubtedly a psychological component.

NICE (1) notes that:

• a diagnosis of IBS should be considered only if the person has abdominal pain or discomfort that is either relieved by defaecation or associated with altered bowel frequency or stool form. This should be accompanied by at least two of the following four symptoms:
  • altered stool passage (straining, urgency, incomplete evacuation)
  • abdominal bloating (more common in women than men), distension, tension or hardness
  • symptoms made worse by eating
  • passage of mucus
    
• other features such as lethargy, nausea, backache and bladder symptoms are common in people with IBS, and may be used to support the diagnosis
  
• all people presenting with possible IBS symptoms should be assessed and clinically examined for the following 'red flag' indicators and should be referred to secondary care for further investigation if any are present:
  • signs and symptoms of cancer in line with the NICE guidance on recognition and referral for suspected cancer
  • inflammatory markers for inflammatory bowel disease
    
• diagnostic tests In people who meet the IBS diagnostic criteria, the following tests should be undertaken to exclude other diagnoses:
  • full blood count (FBC)
  • erythrocyte sedimentation rate (ESR) or plasma viscosity
  • c-reactive protein (CRP)
  • antibody testing for coeliac disease (endomysial antibodies [EMA] or tissue transglutaminase [TTG])
    

Management consists of various measures including explanation, dietary and lifestyle advice, fibre supplements, antispasmodics and antidepressants.

An expert diet review concluded (2):

• Best Practice Advice 1:
  • dietary advice is ideally prescribed to patients with IBS who have insight into their meal-related gastrointestinal symptoms and are motivated to make the necessary changes
  • to optimize the quality of teaching and clinical response, referral to a registered dietitian nutritionist (RDN) should be made to patients who are willing to collaborate with an RDN and patients who are not able to implement beneficial dietary changes on their own
  • if a gastrointestinal RDN is not available, other resources can assist with implementation of diet interventions
• Best Practice Advice 2:
  • patients with IBS who are poor candidates for restrictive diet interventions include those consuming few culprit foods, those at risk for malnutrition, those who are food insecure, and those with an eating disorder or uncontrolled psychiatric disorder
  • routine screening for disordered eating or eating disorders by careful dietary history is critical because they are common and often overlooked in gastrointestinal conditions
• Best Practice Advice 3:
  • specific diet interventions should be attempted for a predetermined length of time
    • if there is no clinical response, the diet intervention should be abandoned for another treatment alternative, for example, a different diet, medication, or other form of therapy
• Best Practice Advice 4:
  • in preparation for a visit with an RDN, patients should provide dietary information that will assist in developing an individualized nutrition care plan
• Best Practice Advice 5:
  • soluble fibre is efficacious in treating global symptoms of IBS
• Best Practice Advice 6:
  • the low-FODMAP diet is currently the most evidence-based diet intervention for IBS. Healthy eating advice as described by the National Institute of Health and Care Excellence Guidelines, among others, also offers benefit to a subset of patients with IBS
• Best Practice Advice 7:
  • the low-FODMAP diet consists of the following 3 phases:
    • 1) restriction (lasting no more than 4-6 weeks),
    • 2) reintroduction of FODMAP foods, and
    • 3) personalization based on results from reintroduction
• Best Practice Advice 8:
  • although observational studies found that most patients with IBS improve with a gluten-free diet, randomized controlled trials have yielded mixed results
• Best Practice Advice 9:
  • are limited data showing that selected biomarkers can predict response to diet interventions in patients with IBS, but there is insufficient evidence to support their routine use in clinical practice.

Notes:

• a study (n=304) found low FODMAP diet plus traditional dietary advice as recommended by NICE, a low-carbohydrate diet, and optimised medical treatment led to a response (reduction ≥50 in IBS Severity Scoring System relative to baseline) in 76%, 71% & 58%, respectively, at 4 weeks (3)
  • a low-carbohydrate diet or a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) plus traditional IBS dietary advice outperformed pharmacological treatment

Reference:

1. NICE (April 2017).Irritable bowel syndrome in adults - diagnosis and management of irritable bowel syndrome in primary care.
2. Chey WD et al. AGA Clinical Practice Update on the Role of Diet in Irritable Bowel Syndrome: Expert Review. Gastroenterology March 2022. https://doi.org/10.1053/j.gastro.2021.12.248
3. Nybacka, Sanna et al. A low FODMAP diet plus traditional dietary advice versus a low-carbohydrate diet versus pharmacological treatment in irritable bowel syndrome (CARBIS): a single-centre, single-blind, randomised controlled trial. Lancet Gastroenterology & Hepatology April 18th 2024.