Clinical Applications of Dietary Therapies in Irritable Bowel Syndrome (IBS)
Rej A, Avery A, Ford AC et al. J Gastrointestinal Liver Disease. 2018; 27 (3): 307-316
Over the last decade, there has been renewed interest in the role of dietary therapies in IBS. Both the British Dietetic Association (BDA) and National Institute for Health and Clinical Excellence (NICE) guidance recommends healthy eating and lifestyle management as first-line advice for IBS. However, recent research has also focused on the role of a low fermentable oligo-, di- and mono- saccharides and polyols (FODMAPs) diet (first study published in 2006), wheat-free diet (WFD) (first study published in 2012) and gluten-free diet (GFD) (first study 2001) in relief of IBS symptoms. A number of unanswered questions about the clinical applications of these dietary therapies exist.
Over the last decade, there has been renewed interest in the role of dietary therapies in IBS. Both the British Dietetic Association (BDA) and National Institute for Health and Clinical Excellence (NICE) guidance recommends healthy eating and lifestyle management as first-line advice for IBS. However, recent research has also focused on the role of a low fermentable oligo-, di- and mono- saccharides and polyols (FODMAPs) diet (first study published in 2006), wheat-free diet (WFD) (first study published in 2012) and gluten-free diet (GFD) (first study 2001) in relief of IBS symptoms. A number of unanswered questions about the clinical applications of these dietary therapies exist.
This review article, based on a roundtable discussion with gastroenterologists and dietitians with a special interest in dietary therapies held in May 2017, aims to provide a practical guide, for healthcare professionals, for the implementation of these dietary strategies in IBS.
First-Line Dietary Therapies
National guidance for IBS (NICE) recommends dietary and lifestyle changes as first-line management for IBS. In 2016, the BDA created an updated set of evidence-based practice guidelines for the dietary management of IBS including assessment of alcohol, caffeine, fat, fluid and spicy food intake, fibre modification as well as checking for milk/lactose intolerance. These interventions are based on evidence graded as level C or D, depending on the dietary therapy, by the BDA.
The low FODMAP Diet
A low FODMAP diet has been recommended as a dietary therapy that can be used in the management of IBS. There have been a number of systematic reviews and meta analyses of the low FODMAP diet in IBS. The first meta-analysis, analysing 6 Randomised Controlled Trials (RCTs) and 16 non-randomised studies, demonstrated its benefits showing a statistically significant decrease in IBS symptom severity scores (IBS-SSS), IBS quality of life (QOL), symptom severity for abdominal pain, bloating and overall symptoms in both the RCTs and non-randomised studies. However, a recent systematic review focusing on the quality of 9 RCTs of a low FODMAP diet in IBS suggested a high risk of bias in trials. Other concerns included small study numbers, recruitment of patients from tertiary centres, as well as issues around blinding and choice of control group. A separate systematic review, including 5 studies of a low FODMAP diet in IBS, deemed that the quality of evidence for the low FODMAP diet was only fair (Level II), with little evidence to support a recommendation for or against a low FODMAP diet in IBS (Grade C) on the basis of studies reviewed.
A number of questions remain. It is still unclear how a low FODMAP diet compares to other dietary therapies as there have been few head-to-head trials. In addition, the majority of research has focused on short-term endpoints and there is a lack of long-term data. The data that does exist shows adherence to the low FODMAP diet appears to be good, with one prospective observational study showing 75% adherence to an adapted low FODMAP diet after a median follow up of 16 months, with 70% of patients satisfied with the symptom improvement. A number of potential risks of a low FODMAP diet have been identified including nutritional adequacy and the effect of the diet on the gut microbiota.
The Wheat-Free Diet (WFD)
A proportion of individuals presenting with IBS symptoms may have sensitivity to wheat. In a large retrospective study involving 920 patients fulfilling the ROME II criteria for IBS, 30% demonstrated wheat sensitivity or multiple food hypersensitivities (including wheat). Wheat-sensitive patients, on an elimination diet, developed symptoms with wheat (given via capsules), using a double-blind, placebo-controlled challenge. Significant increases in the Visual Analogue Scores (VAS) for overall symptoms, bloating, abdominal pain and stool consistency were observed following the wheat challenge. In a separate study, using confocal endomicroscopy, immediate and dramatic mucosal changes to wheat have been noted in patients with IBS.
In a prospective study involving 200 participants from the original study of 920 subjects, 74% were still adhering to a strict WFD at follow-up (median follow up of 99 months). 10% were strictly avoiding wheat but consuming other gluten-containing foods including barley and rye, with the other 64% on a strict GFD. Of the 22 patients who consented to wheat challenge, 20 still reacted to wheat highlighting that wheat sensitivity is likely to be persistent. At present, there is a lack of evidence around the risks of a WFD. As those consuming a WFD commonly commence a GFD, an inference could be made that the risks are similar to those of a GFD, which are discussed in the next section.
The Gluten-Free Diet (GFD)
The concept of patients presenting with symptoms following gluten ingestion, without a diagnosis of coeliac disease, has been described as early as the 1980s. Recent research has assessed the role of a GFD in patients with IBS with a number of studies focusing on patients with IBS-D. Several studies have demonstrated the benefit of a GFD in this patient group in terms of both improvement in IBS-SSS as well as effect on bowel movements. In one study, the effect of a gluten-containing diet (GCD) on bowel movements was greater in HLA-DQ 2/8 positive, compared with negative, patients. An increased bowel permeability in HLA-DQ 2/8 positive patients was also observed, demonstrating that gluten may alter intestinal barrier function in these patients with IBS-D. In another study, a reduction in IBS-SSS was observed in IBS-D patients after 6 weeks on a GFD with similar reductions in both HLA-DQ 2/8 positive and negative subjects. 72% of those with a clinical response were still on a GFD 18 months after the study and intended to continue on the diet.
In several other studies, following commencement of a GFD, a statistically significant lower symptom control was noted following re-introduction of gluten vs placebo, showing patients are likely to be sensitive to gluten. A number of potential risks of a GFD exist including concerns regarding the nutritional adequacy of a GFD and effect on gut microbiota. The cost of a GFD is also a potential concern.
In summary, the evidence to date indicates that one diet alone is not effective for all patients with IBS, reinforcing the underlying heterogeneity of this condition. Questions remain as to the causal agent in triggering symptoms in IBS, however, regardless of the mechanism there appears to be variable evidence for the use of all of the diets in clinical practice. These dietary therapies should be delivered by a dietitian with a special interest in IBS. The decision-making process for using each individual diet should be directed by a detailed history, taken by a dietitian, and involve the patient in the process.
First-Line Dietary Therapies
National guidance for IBS (NICE) recommends dietary and lifestyle changes as first-line management for IBS. In 2016, the BDA created an updated set of evidence-based practice guidelines for the dietary management of IBS including assessment of alcohol, caffeine, fat, fluid and spicy food intake, fibre modification as well as checking for milk/lactose intolerance. These interventions are based on evidence graded as level C or D, depending on the dietary therapy, by the BDA.
The low FODMAP Diet
A low FODMAP diet has been recommended as a dietary therapy that can be used in the management of IBS. There have been a number of systematic reviews and meta analyses of the low FODMAP diet in IBS. The first meta-analysis, analysing 6 Randomised Controlled Trials (RCTs) and 16 non-randomised studies, demonstrated its benefits showing a statistically significant decrease in IBS symptom severity scores (IBS-SSS), IBS quality of life (QOL), symptom severity for abdominal pain, bloating and overall symptoms in both the RCTs and non-randomised studies. However, a recent systematic review focusing on the quality of 9 RCTs of a low FODMAP diet in IBS suggested a high risk of bias in trials. Other concerns included small study numbers, recruitment of patients from tertiary centres, as well as issues around blinding and choice of control group. A separate systematic review, including 5 studies of a low FODMAP diet in IBS, deemed that the quality of evidence for the low FODMAP diet was only fair (Level II), with little evidence to support a recommendation for or against a low FODMAP diet in IBS (Grade C) on the basis of studies reviewed.
A number of questions remain. It is still unclear how a low FODMAP diet compares to other dietary therapies as there have been few head-to-head trials. In addition, the majority of research has focused on short-term endpoints and there is a lack of long-term data. The data that does exist shows adherence to the low FODMAP diet appears to be good, with one prospective observational study showing 75% adherence to an adapted low FODMAP diet after a median follow up of 16 months, with 70% of patients satisfied with the symptom improvement. A number of potential risks of a low FODMAP diet have been identified including nutritional adequacy and the effect of the diet on the gut microbiota.
The Wheat-Free Diet (WFD)
A proportion of individuals presenting with IBS symptoms may have sensitivity to wheat. In a large retrospective study involving 920 patients fulfilling the ROME II criteria for IBS, 30% demonstrated wheat sensitivity or multiple food hypersensitivities (including wheat). Wheat-sensitive patients, on an elimination diet, developed symptoms with wheat (given via capsules), using a double-blind, placebo-controlled challenge. Significant increases in the Visual Analogue Scores (VAS) for overall symptoms, bloating, abdominal pain and stool consistency were observed following the wheat challenge. In a separate study, using confocal endomicroscopy, immediate and dramatic mucosal changes to wheat have been noted in patients with IBS.
In a prospective study involving 200 participants from the original study of 920 subjects, 74% were still adhering to a strict WFD at follow-up (median follow up of 99 months). 10% were strictly avoiding wheat but consuming other gluten-containing foods including barley and rye, with the other 64% on a strict GFD. Of the 22 patients who consented to wheat challenge, 20 still reacted to wheat highlighting that wheat sensitivity is likely to be persistent. At present, there is a lack of evidence around the risks of a WFD. As those consuming a WFD commonly commence a GFD, an inference could be made that the risks are similar to those of a GFD, which are discussed in the next section.
The Gluten-Free Diet (GFD)
The concept of patients presenting with symptoms following gluten ingestion, without a diagnosis of coeliac disease, has been described as early as the 1980s. Recent research has assessed the role of a GFD in patients with IBS with a number of studies focusing on patients with IBS-D. Several studies have demonstrated the benefit of a GFD in this patient group in terms of both improvement in IBS-SSS as well as effect on bowel movements. In one study, the effect of a gluten-containing diet (GCD) on bowel movements was greater in HLA-DQ 2/8 positive, compared with negative, patients. An increased bowel permeability in HLA-DQ 2/8 positive patients was also observed, demonstrating that gluten may alter intestinal barrier function in these patients with IBS-D. In another study, a reduction in IBS-SSS was observed in IBS-D patients after 6 weeks on a GFD with similar reductions in both HLA-DQ 2/8 positive and negative subjects. 72% of those with a clinical response were still on a GFD 18 months after the study and intended to continue on the diet.
In several other studies, following commencement of a GFD, a statistically significant lower symptom control was noted following re-introduction of gluten vs placebo, showing patients are likely to be sensitive to gluten. A number of potential risks of a GFD exist including concerns regarding the nutritional adequacy of a GFD and effect on gut microbiota. The cost of a GFD is also a potential concern.
In summary, the evidence to date indicates that one diet alone is not effective for all patients with IBS, reinforcing the underlying heterogeneity of this condition. Questions remain as to the causal agent in triggering symptoms in IBS, however, regardless of the mechanism there appears to be variable evidence for the use of all of the diets in clinical practice. These dietary therapies should be delivered by a dietitian with a special interest in IBS. The decision-making process for using each individual diet should be directed by a detailed history, taken by a dietitian, and involve the patient in the process.
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