Irritable bowel syndrome (IBS) is a common functional bowel disorder characterized by chronic abdominal pain, bloating, and altered bowel habit. Dietary therapies are frequently recommended in IBS, given that over 80% of individuals report food-related symptoms.
Irritable bowel syndrome (IBS) is a common functional bowel disorder characterized by chronic abdominal pain, bloating, and altered bowel habit. Dietary therapies are frequently recommended in IBS, given that over 80% of individuals report food-related symptoms.
Dietary guidelines for IBS recommend following a balanced eating pattern with a focus on whole, plant-based foods and lean protein sources as a first-line intervention. This first-line approach, referred to as Traditional Dietary Advice (TDA) in the UK, also emphasizes reducing intake of fatty and spicy foods, sweeteners and artificial sweeteners, caffeine, alcohol, and gas-producing foods. The low FODMAP diet (LFD) is often recommended as a second-line intervention for IBS and reduces dietary short-chain, fermentable carbohydrates found in fruits, vegetables, dairy products, artificial sweeteners and some grains. The LFD’s three-phased protocol helps identify which FODMAPs, if any, exacerbate IBS symptoms and should be avoided long-term. A gluten-free diet (GFD) has also grown in popularity for the management of functional gut symptoms, including IBS.
A recent randomized control trial in the UK compared these three dietary approaches (TDA, the LFD and GFD) to investigate the efficacy, acceptability, nutritional and stool microbial changes associated with each diet.
Methods
Adults ≥ 18 years, Rome IV IBS-Diarrhea (IBS-D) or mixed type (IBS-M), and an IBS-symptoms severity score of >75 were recruited from two secondary care centers in the UK. Patients were randomized to a TDA, LFD or GFD group. Participants were seen face-to-face by registered dietitians and dietary advice was provided using a standardized 45-60 minute presentation, dietary info sheets and time for questions. During the Covid-19 pandemic, this process became a virtual consultation, using the same materials. Participants followed their diets for 4 weeks, with outcomes at week 4 compared with baseline.
Questionnaires completed pre- and post-intervention, included:
- IBS symptom severity score (IBS-SSS)
- Hospital Anxiety & Depression Scale
- Patient health questionnaire
- IBS quality of life (QoL) questionnaire
- Acceptability of dietary restriction questionnaire
- Food-related QoL questionnaire
- Comprehensive Nutrition Assessment Questionnaire
Stool samples for assessment of dysbiosis were collected for 50% of patients (Covid-19 prevented collection of remaining samples)
Key Findings
A total of 99 participants, 33 per arm, completed the study. There was no difference in base-line variables across groups. Mean age was 37 years, 71% female, 88% white, 75% IBS-D, 25% IBS-M. Nine percent of participants had mild IBS, 47% moderate IBS and 45% severe IBS (p=0.5 across all groups).
The diets did not significantly differ in clinical efficacy. The primary endpoint of ≥50-point reduction in IBS-SSS was met by 42% taking TDA, 55% with LFD, and 58% with GFD, with no significant difference across groups; p=0.43.
The modes of dietary education, either face-to-face or virtual, were equally effective: A ≥50-point reduction in IBS-SSS was seen in 52% receiving face-to-face consult vs. 51% receiving live virtual consult; p=0.98.
There was no statistical difference in response rates between IBS-D vs. IBS-M based on a particular dietary therapy. A ≥50-point reduction in IBS-SSS was seen in 54% (n=40/74) with IBS-D vs. 44% (n=11/25) with IBS-M, with no difference between groups; p=0.38.
Individuals found TDA cheaper, less time-consuming to shop, and easier to follow when eating out. Individuals found TDA and GFD easier to incorporate into their life than the LFD (p=0.02). The proportion of individuals who would consider continuing the diets were 70% for TDA, 67% for LFD and 61% for GFD, with no difference across groups (p=0.73).
FODMAP intake was reduced across all groups. Significant within-group reduction in total FODMAP intake occurred with all three diets. The greatest reduction was seen with the LFD (27.7g/day pre-intervention to 7.6g/day at week 4) compared with TDA (24.9g/day to 15.2g/day) and GFD (27.4g/day to 22.4g/day); p<0.01.
Changes in dysbiosis index (DI) did not differ across groups. 22-29% of participants experienced an improvement, 35-39% had no change, and 35-40% had worsening DI. Changes in DI did not differ between responders and non-responders.
Discussion & conclusions
TDA, GFD and LFD are effective approaches in non-constipated IBS. The authors of this study recommend TDA as the first-choice dietary option due to its widespread availability and patient friendliness. The LFD or GFD are alternative options based on specific patient preferences and with specialist counselling from a registered dietitian. Current clinical guidelines do not recommend a GFD for the management of IBS, however, the results of this study suggest that an evaluation of the GFD in patients not responding to TDA may be warranted.
The diets implemented in this study reduced total FODMAP intake, mostly in the LFD group compared with TDA and GFD. This suggests a degree of overlap and that moderate FODMAP restriction, as seen with TDA and a GFD, may be similarly effective as a strict LFD. The LFD is a 3-phase intervention and data suggests that patients may fail to move from the strict elimination phase to the reintroduction and personalization phases, which puts them at risk of overly restrictive eating patterns and nutritional inadequacies.1 There are suggestions that a ‘bottom-up’ or “FODMAP-gentle” approach to the LFD may be sufficient to identify symptom-triggering foods. For example, in the long-term, many patients on a personalized LFD reduce fructan intake to manage their symptoms, which means they seek gluten- or wheat- free products.2 Therefore, a GFD may be an option to trial before implementing the full LFD. Furthermore, this study, along with another recent publications, suggests that a GFD in IBS does not need to be as strict as one used for celiac disease. Future studies should determine the level of gluten restriction required to derive symptom benefit for patients with IBS where celiac disease has been ruled out.
Further references:
- 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.
- 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 Nov;53(11):1404-1411