Dietary therapies in irritable bowel syndrome: an update

Christian Shaw and Rachel Buckle are Trainee Advanced Clinical Practitioner’s and Specialist Gastroenterology Dietitian’s at Sheffield Gastroenterology.

Irritable bowel syndrome (IBS) is a condition frequently presenting to primary care, accounting for 1 in 12 of all consultations.1 Therefore, the GP will be the first point of contact; diagnosing and initiating treatments for most of these patients. As IBS is a chronic condition, many patients will re-present to healthcare services; therefore, effective management options are important to relieve symptom burden, improve quality of life, and reduce pressure on healthcare services.

The current treatment includes medical management, dietary therapies, and psychological support. Guidelines advocate a two-stepped approach for dietary management, including traditional dietary advice (TDA) often referred to as ‘first line’ advice,2 followed by a low fermentable oligo-, di-, mono-saccharides and polyols diet or FODMAP diet (LFD) as ‘second line’. British Society of Gastroenterology (BSG) guidelines advocate ‘first line’ advice as a simple step in symptom management following diagnosis, which can be delivered in primary care. TDA is based around dietary and lifestyle recommendations from the British Dietetic Association (BDA) IBS guidelines published in 2016.2 This includes healthy eating and lifestyle changes, reductions in dietary fat, spicy food, caffeine, alcohol, and lactose avoidance, if this is suspected as a symptom trigger.

“As IBS is a chronic condition, many patients will re-present to healthcare services”

Previous research supports the use of TDA and the LFD at short-term follow-up.3 As IBS is a chronic condition, management needs to be effective in the long term; however, there is a lack of long-term data on TDA, whereas growing evidence supports the LFD. The latest was from the largest multicentre study on the effects of the LFD conducted by the Sheffield Gastroenterology group.4 At up to 8-years follow-up, 60% of patients using the LFD had adequate symptom relief. Symptom response was better with higher self-reported adherence, with 68% with strict adherence having relief compared with only 13% with major lapses from the diet, suggesting adherence is important.

Although the LFD results are promising, it requires a significant investment of patient time, as it can take 4–6 months to complete all three stages of the diet. It is also challenging to implement, as only 65% can follow all three stages appropriately even if seen by a dietitian, with a figure much lower at 29% if the advice was given without dietetic involvement.5 Furthermore, concerns have been raised regarding the use of restrictive diets in those with disordered eating,6 which should be screened for in those with IBS.

Interestingly, Sheffield Gastroenterology group noted 68% of patients following the LFD at long-term follow-up use gluten-free (GF) or wheat-free (WF) products, and 43% follow these diets when eating out. Previous randomised controlled trials (RCTs) have shown the GF diet to be effective at managing IBS symptoms in the short term, with a lack of data on the long-term efficacy.3 Fructans, a component of LFD, escape absorption in the small intestine and undergo colonic fermentation, which may contribute to symptoms in IBS. As wheat-based products are the largest contributor of fructans in the UK diet, using GF products may reduce total fructan intake as they contain lower quantities compared to gluten containing alternatives. This may be driving symptom relief in some individuals with IBS.

In response, the Sheffield Gastroenterology group conducted the first RCT comparing TDA, LFD, and the GF diet.7 In total, 99 patients with non-constipated IBS were randomised to one diet for a 4-week intervention period. Traditional dietary advice was given as per BDA guidelines, and the GFD was adapted for IBS where all cereal grains containing gluten were avoided, but cross contamination was permitted. Advice for each diet was delivered in a group setting by FODMAP-trained senior gastroenterology dietitians with a clinical interest in IBS.

“Although the LFD results are promising, it requires a significant investment of patient time … “

The primary outcome was clinical response in the IBS-Severity Scoring System questionnaire. This was achieved by 42% of patients who received TDA, 55% for LFD, and 58% for GFD. The difference between the groups was not significant (P = 0.43), indicating all three dietary therapies were equally effective and should be considered as management options for patients with IBS,7 with first line advice or TDA being an effective treatment that GPs could recommend at diagnosis, with a referral onto a dietitian for a more personalised approach or sign posting to online services.

Due to healthcare service pressures webinars are becoming popular. Due to COVID-19 we switched to online groups and saw no difference in clinical response, suggesting this is an effective method of delivery.7 Online resources are available from BDA to support the delivery of first line advice in primary care.

When considering a diagnosis of IBS please refer to the National Institute for Health and Care Excellence irritable bowel syndrome in adults: diagnosis and management guidelines.8 Red flags for colorectal cancer, which should prompt further investigation and referral to secondary care, include:

• Aged ≥40 years with unexplained weight loss and abdominal pain; or
• they are aged ≥50 years with unexplained rectal bleeding; or
• they are aged ≥60 years with:

— iron deficiency anaemia (IDA); or
— changes in their bowel habit.

• Tests show occult blood in their faeces.
• Rectal or abdominal mass.
• Consider referral in those aged <50 years with rectal bleeding with any of the following:

— abdominal pain;
— change in bowel habit;
— weight loss; or
— iron deficiency anaemia.

Useful details
BDA resources are available from:

1. Thompson WG, Heaton KW, Smyth GT, Smyth C. Irritable bowel syndrome in general practice: prevalence, characteristics, and referral. Gut 2000; 46(1): 78–82.
2. McKenzie YA, Bowyer RK, Leach H, et al. British Dietetic Association systematic review and evidence-based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update). J Hum Nutr Diet 2016; 29(5): 549–575.
3. Rej A, Avery A, Ford AC, et al. Clinical application of dietary therapies in irritable bowel syndrome. J Gastrointestin Liver Dis 2018; 27(3): 307–316.
4. Rej A, Shaw CC, Buckle RL, et al. The low FODMAP diet for IBS; a multicentre UK study assessing long term follow up. Dig Liver Dis 2021; 53(11): 1404–1411.
5. Tuck CJ, Reed DE, Muir JG, Vanner SJ. Implementation of the low FODMAP diet in functional gastrointestinal symptoms: a real‐world experience. Neurogastroenterol Motil 2020; 32(1): e13730.
6. Riehl ME, Scarlata K. Understanding disordered eating risks in patients with gastrointestinal conditions. J Acad Nutr Diet 2022; 122(3): 491–499.
7. Rej A, Sanders DS, Shaw CC, et al. Efficacy and acceptability of dietary therapies in non-constipated irritable bowel syndrome: a randomized trial of traditional dietary advice, the low FODMAP diet, and the gluten-free diet. Clin Gastroenterol Hepatol 2022; DOI: 10.1016/j.cgh.2022.02.045.
8. National Institute for Health and Care Excellence. Irritable bowel syndrome in adults: diagnosis and management. 2017. (accessed 15 Sep 2022).

Featured photo by Zura Narimanishvili on Unsplash.

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