Dietary management of irritable bowel syndrome: considerations, challenges, and solutions

Abstract

Diet is a cornerstone in the management of irritable bowel syndrome (IBS). There is evidence of efficacy across the spectrum of dietary management strategies, including some supplements (eg, specific fibres), foods, and whole diets (eg, a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols [known as the low-FODMAP diet]). Whole-diet interventions, in particular those that restrict intake, can be challenging to deliver effectively and safely. Factors to consider include patient demographics, food cost and availability, and the acceptability of dietary management and its impact on food-related quality of life. There is concern regarding a potential role of restrictive whole-diet interventions in eating disorder risk. Optimal approaches to delivering dietary management in the health-care setting are unclear. The aim of this Review is to summarise the clinical evidence for the dietary management of IBS; to discuss the challenges, burdens, and risks of dietary management; and to propose how these challenges, burdens, and risks should be mitigated and minimised in clinical practice.

Introduction

Irritable bowel syndrome (IBS) is a disorder of gut–brain interaction with a global prevalence of around 4·1%¹ and is characterised by recurrent abdominal pain associated with a change in either stool frequency or consistency.² IBS pathophysiology is incompletely understood, but involves altered gut physiology via the gut–brain axis, including an altered gut microbiome, changes in gut motility, and heightened visceral sensitivity to luminal content.² Although not life-threatening, IBS is not a benign disorder. Compared with healthy people without IBS, those with IBS report impairments across all domains of health-related quality of life,³ and anxiety and depression have been separately reported in 23% of people with IBS.⁴ Management of IBS can include symptom-directed pharmacotherapy⁵ and psychological management of the gut–brain axis.⁶

Diet has become a cornerstone of IBS management, driven by an increase in research supporting its use and the preference among patients for non-pharmaceutical strategies to alleviate symptoms.⁷ Although diet might be viewed as a low-cost, low-burden, low-risk intervention, there are challenges that clinicians should consider before recommending dietary management for a person with IBS. The aim of this Review is to summarise clinical evidence for the dietary management of IBS; to discuss the challenges, burdens, and risks of dietary management; and to propose how these challenges, burdens, and risks should be mitigated and minimised in clinical practice.

Current evidence for dietary management

Many people with IBS attribute their symptoms to components of their diet.⁸ Dietary management can occur across a spectrum ranging from supplements in the form of sachets, tablets, capsules, or gummies (eg, fibres and prebiotics), foods (increase or decrease in quantity or modification in the type of one or two foods), or whole-diet interventions (increase or decrease in quantity or modification in the type of multiple foods). The evidence for these interventions is compiled in table 1.

Table 1:

Meta-analyses of the effect of diet interventions on global IBS symptoms in adults

	Studies in the meta-analysis	Number of patients	Comparator	Reported effect
Ispaghula husk (psyllium), up to 10 g/day	7 RCTs summarised in a meta-analysis9	499	Placebo or low-fibre diet	RR of persistence of global IBS symptoms 0·83 (95% CI 0·73 to 0·94)
Wheat bran, up to 10 g/day	6 RCTs summarised in a meta-analysis9	411	Placebo	RR of persistence of global IBS symptoms 0·90 (95% CI 0·79 to 1·03)
Prebiotics (eg, inulin and galacto-oligosaccharides)	11 RCTs summarised in a meta-analysis (8 in IBS, 3 in other functional bowel disorders)10	729	Placebo	OR for global IBS symptom response 0·62 (95% CI 0·07 to 5·69); SMD for global IBS symptoms scores –0·39 (95% CI –1·43 to 0·64)
BDA and NICE diet	5 RCTs summarised in a network meta-analysis11	237	Habitual diet* and sham diet*	RR of persistence of global IBS symptoms 0·82 (95% CI 0·57 to 1·18) versus habitual diet and 0·87 (95% CI 0·61 to 1·23) versus sham diet
Low-FODMAP diet	13 RCTs summarised in a network meta-analysis11	944	BDA and NICE diet, sham diet, and habitual diet	RR of persistence of global IBS symptoms 0·81 (95% CI 0·67 to 0·97) versus BDA or NICE diet, 0·70 (0·52 to 0·95) versus sham diet, and 0·67 (0·48 to 0·91) versus habitual diet
Gluten-free diet (in responders to diet)	2 RCTs summarised in a meta-analysis12	111	Diet spiked with gluten	RR of persistence of global IBS symptoms 0·42 (95% CI 0·11 to 1·55)

BDA=British Dietetic Association. FODMAP=fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. IBS=irritable bowel syndrome. NICE=National Institute for Health and Care Excellence. OR=odds ratio. RCT=randomised controlled trials. RR=relative risk. SMD=standardised mean difference.

^*No direct comparison with BDA and NICE diet; estimates derived from indirect evidence from a network meta-analysis.¹¹

Supplements

Dietary fibres are naturally occurring, extracted, or synthetic carbohydrate polymers that are not hydrolysed by endogenous enzymes in the small intestine of humans, and usually consist of ten or more monomeric units, although some national authorities define this as three or more monomers.¹³ Fibres can be described as soluble or insoluble, although categorisation based on other physicochemical characteristics (eg, viscosity or fermentability) is more relevant to their functional effects in the gut.¹⁴ Fibre might have beneficial effects in IBS arising from increasing stool bulk, accelerating gastrointestinal transit, and modulating gut microbiota.¹⁴ The majority of clinical trials of fibre in IBS use dietary supplements. In a meta-analysis of 14 randomised controlled trials (RCTs), ispaghula husk (psyllium), a viscous and partially fermentable fibre, was of global benefit in people with IBS, but bran was no better than placebo (table 1).⁹ Best practice recommendations, based on expert opinion only, advise that fibre supplements are commenced at a low dose, usually half of the full dose, which is increased slowly to optimise tolerability—eg, by 3 g/day every 2 weeks.

Prebiotics are non-digestible, fermentable food components that selectively stimulate the growth or activity of particular gut microbiota that confer health benefits to the host.¹⁵ Examples include inulin, oligofructose, and galacto-oligosaccharides. Prebiotics are found in foods such as chicory, alliums, artichokes, and pulses, but, to our knowledge, all trials that have investigated the utility of prebiotics in improving symptoms of IBS have used supplements rather than food or whole-diet interventions.¹⁰ In a meta-analysis of 11 RCTs of prebiotic supplements in adults with IBS (or other functional bowel disorders), no significant differences were found between prebiotics and placebo in terms of global symptom responder rates or effect on global symptom scores.¹⁰ However, there was heterogeneity between studies and too few RCTs to ascertain whether a particular prebiotic was beneficial.

Foods

An alternative to supplements to achieve a high-fibre diet is the use of high-fibre foods. In a trial in which 56 people with IBS were randomly assigned to a high-fibre breakfast cereal and two apples per day (30·5 g/day of fibre) or a low-fibre diet (10·4 g/day), symptoms decreased from baseline in both groups but there were no significant differences between the groups.¹⁶

Fermented foods are made through desired microbial growth and enzymatic conversions of food components.¹⁷ Common examples include kefir, kombucha, sauerkraut, and kimchi. In a pilot RCT of pasteurised versus unpasteurised sauerkraut supplement in 34 people with IBS, both interventions led to significant improvements in symptom scores, with no difference between groups.¹⁸ In another RCT (n=90) of three types of kimchi (standard kimchi, kimchi fermented with dead bacteria, and kimchi fermented with live bacteria), IBS symptoms improved from baseline in all three groups, but with no difference between groups.¹⁹ Taken together, there is currently no evidence of an additional benefit of fermented foods over their unfermented versions in the treatment of IBS.

Green kiwifruit has been evaluated in people with constipation-predominant IBS due to its laxative-enhancing components (eg, fibre and raphides). Two RCTs of kiwifruit (two fruits per day) both reported increases in stool frequency but no differences compared with either psyllium or placebo capsule in participants with constipation-predominant IBS.^20,21

Whole-diet interventions

Whole-diet interventions have also been tested in IBS. First-line dietary advice for IBS from both the British Dietetic Association (BDA) and the National Institute for Health and Care Excellence (NICE) includes eating regular small meals, consuming adequate fluids, whilst limiting alcohol, reducing caffeine, fizzy drinks and fatty foods.²² Although often used as comparator interventions in dietary trials in IBS,¹¹ BDA and NICE dietary advice has never been compared with a control intervention; hence, direct evidence of a benefit in IBS is lacking. Another whole-diet intervention that has been studied in IBS is the Mediterranean diet, which is characterised by high intakes of wholegrains, fruits, vegetables, legumes, extra-virgin olive oil, and fish, switching alcohol to moderate intake of wine (where consumed), and low intakes of red meat and processed foods. A 4-week, non-randomised, three-arm trial in 42 people with IBS²³ and a 6-week, unblinded feasibility trial in 59 people with IBS (together with mild or moderate symptoms of depression, anxiety, or both)²⁴ have been conducted. Both report high levels of adherence and improvements in global and individual gastrointestinal symptoms with the Mediterranean diet. Adequately powered RCTs of the Mediterranean diet are required in IBS.

Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) induce symptoms in many people with IBS.²⁵ FODMAPs are present in specific fruits, vegetables, and legumes, and some polyols are used as artificial sweeteners. Unabsorbed fructose, polyols, and lactose can increase small intestinal water, and fructans and galacto-oligosaccharides, which are indigestible, undergo colonic fermentation. A low-FODMAP diet consists of three phases: FODMAP restriction for 4–6 weeks; reintroduction of individual FODMAP-containing foods to assess tolerance; and personalisation to create a modified FODMAP-containing diet based on tolerance to foods identified in the second phase.²⁶ Several RCTs have compared the efficacy of the first phase of the diet with various other interventions, including NICE dietary advice,²⁷ a habitual diet,²⁸ and a sham diet,²⁹ in people with IBS. In a meta-analysis of seven RCTs in IBS, a low-FODMAP diet was associated with symptom benefit compared with control interventions and a habitual diet, but was no different to alternative whole-diet interventions.¹² In a network meta-analysis of 13 trials (12 trials providing data), a low-FODMAP diet ranked first and was superior for global symptom benefit in IBS versus a range of alternative dietary interventions.¹¹ BDA or NICE dietary advice ranked second, although was not superior to any other intervention.¹¹ Subsequent to this network meta-analysis, an RCT in 294 people with moderate-to-severe IBS showed that a low-FODMAP diet plus NICE dietary advice and a fibre-optimised, low-carbohydrate diet both resulted in greater response rates than optimised medical treatment (based on predominant IBS symptom), although comparisons with optimised medical treatment were only made at 4 weeks.³⁰ Use of the low-FODMAP diet in conjunction with food supplements has been investigated in IBS, showing similar or improved efficacy with the co-administration of probiotics,²⁹ prebiotics,³¹ fibre,³² or glutamine.³³

Instead of a strict low-FODMAP diet, in practice some health professionals use a less restrictive low-FODMAP diet in the first instance, in which only selected FODMAPs or high-FODMAP foods are restricted (sometimes referred to as FODMAP-light or FODMAP-gentle). A framework for how this approach can be applied in practice has been proposed.³⁴ A small, double-blind RCT in participants with diarrhoea-predominant IBS found that a FODMAP-light diet (restricted only in fructans and galacto-oligosaccharides) resulted in ten (63%) of 16 individuals having a reduction in symptom severity of more than 30% for at least 2–4 weeks (ie, a response according to Food and Drug Administration criteria), compared with nine (56%) of 16 individuals on a traditional low-FODMAP diet.³⁵ In an RCT conducted in 459 patients with IBS recruited from primary care, a smartphone-based FODMAP-lowering dietary education (simplified version of the strict low-FODMAP diet) significantly improved IBS symptom responder rates compared with otilonium bromide (an antispasmodic drug) as first-line treatments for IBS.³⁶

Wheat-restricted or gluten-restricted diets have also been trialled in IBS. Wheat avoidance due to perceived (often gastrointestinal) side-effects has been reported in 7% of the general adult population in Australia.³⁷ In one study of 330 individuals with IBS, 81 (25%) reported that wholemeal products provoked their symptoms, 63 (19%) white bread, and 51 (16%) crispbread.³⁸ The component of wheat that could trigger gastrointestinal symptoms is unclear, but could include proteins, such as gluten or amylase–trypsin inhibitors, or FODMAPs, as wheat contains fructan. In one RCT, people with IBS who reported symptom improvement on a gluten-free diet were given a 2-week diet of reduced FODMAPs and then either a high-gluten, low-gluten, or control (whey protein) diet for 1 week.³⁹ Gastrointestinal symptoms significantly improved during reduced FODMAP intake, but blinded gluten challenge did not increase symptoms more than the control,³⁹ suggesting that a reduction in fructan might potentially explain the benefit of a gluten-free diet. A previous meta-analysis identified only two RCTs of a gluten-free diet in IBS, which randomly assigned responders to a gluten-free diet to either continue the diet or have their diets spiked with gluten.¹² Although both trials showed a benefit in terms of the number of individuals with improved global symptoms while continuing a gluten-free diet, when data were pooled the effect was not significant, probably due to heterogeneity. A 2022 trial in IBS comparing a gluten-free diet with BDA or NICE dietary advice or a low-FODMAP diet found no significant differences in symptom response rates between the three interventions.⁴⁰

Supplements, foods, and whole-diet interventions in IBS in clinical practice

In general, data from meta-analyses in IBS suggest that effect sizes of benefit for some supplements (eg, wheat bran and prebiotics) are relatively small or non-existant, but for some whole-diet interventions (eg, low-FODMAP diet) are larger (table 1). Although there might be convincing mechanistic rationale for some whole-diet interventions, this pattern could be the result of fewer and sometimes smaller trials in whole-diet interventions, with greater difficulty in blinding meaning a tendency towards positive findings compared with control or comparator groups⁴¹ and a greater potential for publication bias.

There are advantages and disadvantages of different dietary approaches, ranging from the high precision and low dietary impact of supplements to lower precision and higher dietary impact of whole-diet interventions (figure 1). Other issues relate to patient experience, including acceptability, feasibility, and cost, all of which might impact adherence, safety, and clinical effectiveness. For example, in comparison with supplements that might require taking only one or two sachets per day, whole-diet interventions can be more challenging as they require extensive and sometimes complex changes to shopping, cooking, and mealtimes in the home, and reducing or changing social eating behaviours. Eating habits are influenced by a wide range of internal factors (eg, age, sex or gender, socioeconomic status, ethnicity, religion, culture, and previous dietary experiences (eg, foods perceived to cause symptoms may be avoided) and external factors (eg, family preferences, food cost and availability, and advertising).

Figure 1: Advantages and disadvantages of supplements, foods, and whole-diet interventions in IBS.

Many of the disadvantages of all interventions can be mitigated by advice and support from a health professional, including for whole-diet interventions by a dietitian with expertise in IBS management. FODMAPs=fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. IBS=irritable bowel syndrome.

Demographic characteristics and diet management in IBS

Sex and gender are important considerations in the assessment and management of IBS. There are sex differences in how individuals experience IBS. For example, women have lower thresholds for visceral pain perception and are generally more likely than men to disclose symptoms to others, seek health care for their symptoms,⁴² and change their diets to manage symptoms.⁴³ Sex and gender should be incorporated into the dietetic consultation as they have implications for nutritional assessment (eg, sex-specific calculation of energy requirements) and approach to counselling (eg, health beliefs, food choices, and eating behaviours can vary by sex and gender).⁴⁴ Although there are data to suggest that women are more likely than men to be provided lifestyle advice from physicians for their IBS,⁴⁵ no studies have evaluated whether there are sex or gender differences in symptom responses to dietary management.

Age is also a key demographic variable to consider in dietary treatment of IBS. Although restrictive diets can be feasible, safe, and effective in older individuals with gastrointestinal symptoms,⁴⁶ they should generally be recommended with caution due to altered nutritional requirements and the risk of malnutrition in this group. Educational attainment, socioeconomic status, and health literacy could influence understanding of verbal and written information and subsequent ability to adhere to dietary advice, although the association of these factors with diet adherence and symptom outcomes from dietary management has not been studied in IBS. Clinicians are recommended to use clear, jargon-free language and create and provide written resources that meet the literacy needs of each patient.

Ethnicity, culture, and religion are key considerations in the dietary assessment and treatment of people with IBS. These factors can strongly influence food choices, eating behaviours, and the intrinsic values assigned to foods. For example, ancient medicinal practices, such as traditional Chinese medicine (eg, cold or hot foods), might be key components of a patient’s self-management strategy and must be considered when personalising dietary advice. Cultural and religious festivals and traditions also shape dietary behaviours, such as through the consumption of symbolic meals; changes to the way food is served; periods of fasting (eg, Islam), which in some circumstances can be followed by overeating during non-fasting periods; and periods of restricting the quantity of foods and the frequency of eating (eg, Orthodox Christianity). In some cultures, staple foods or food groups can be high in symptom-triggers (eg, onions and legumes are high in some FODMAPs), but there are few studies of the FODMAP content of foods commonly eaten by diverse ethnic groups. Although efficacy trials have shown the benefit of the low-FODMAP diet in reducing symptoms in populations outside of Australia, North America, and Europe with IBS,^47,48 more research is needed to confirm efficacy, feasibility, and acceptability across a range of populations. One potential solution for those consuming a diet naturally high in FODMAPs is to use a FODMAP-light approach.³⁴ All clinicians working in IBS are recommended to strive for cultural competence (ie, attaining the skills that lead to effective communication across cultures), which, among other things, involves improved cultural diet knowledge.

Food cost and availability

Cost and availability of treatment are two major and related determinants of acceptability and adherence. Data on the socioeconomic status of people with IBS are scarce. Food insecurity, defined as the lack of “regular access to enough safe and nutritious food for normal growth and development and an active and healthy life… due to unavailability of food or lack of resources to obtain food”⁴⁹ is sensitive to geopolitical economic fluctuations, and is known to be common among people with inflammatory bowel disease (IBD) and mental ill health,^50,51 which commonly co-occur with IBS. Therefore, although data on food insecurity are currently not available in IBS, it is likely to be prevalent, and clinicians should consider whether it might be a barrier to implementing supplement, food, or whole-diet interventions.

Special food products required in some whole-diet interventions for IBS are costlier and less available than standard options; for example, gluten-free diets, wheat-free diets, and low-FODMAP diets can be considerably more expensive. A report from the UK revealed that gluten-free bread was four times more expensive than regular bread and that a gluten-free weekly shop was 20% more costly than a standard weekly shop.⁵² Similar data suggest that gluten-free versions of wheat-based foods are up to five times more costly than standard counterparts.⁵³ Unfortunately, full economic analyses are rarely performed in clinical trials of dietary management. In one 4-week RCT comparing three whole-diet interventions in participants with non-constipated IBS, 82% of patients reported that a low-FODMAP diet and a gluten-free diet were more expensive than their usual diet.⁴⁰ Data from a long-term follow-up study show very similar results, in that most patients reported that the low-FODMAP diet was more expensive than their usual diet.⁵⁴ Despite these findings, dietary management can still be cheaper than many drugs, although the cost of whole-diet interventions is always borne by the patient. whereas in some health-care systems prescription medication is free, subsidised, or covered by insurance.

Despite the lack of data to date, it is likely that the additional cost associated with the dietary management of IBS, as well as that associated with follow-up for medical or dietetic consultations, will be prohibitive for some individuals. Cost must be considered during the diet assessment and counselling process.

Acceptability and food-related quality of life

Changing eating habits is not simple and often requires considerable lifestyle alterations for the patient, including changing shopping location and food brands, learning about food composition and product identification, and changing methods of food preparation, all of which can impact the acceptability of food and whole-diet interventions.

Numerous studies have measured the acceptability of diet interventions in IBS. In a longitudinal follow-up of 103 patients with IBS in the UK, compared with habitual diets at baseline, a low-FODMAP diet did not stop individuals from being able to shop at their usual supermarket, nor did it require extra time for shopping and cooking.⁵⁵ However, another study in Italy reported that the low-FODMAP diet took longer for both shopping and cooking for people with IBS.⁵⁶

People do not solely eat food because of its nutritional or organoleptic properties (ie, taste, smell, and appearance) but also because of its wider social and psychological roles. These roles include using food as a reward, a coping mechanism, and as a means of interacting and celebrating with family and friends. The extent to which these psychosocial roles of food, eating, and drinking bring enjoyment to peoples’ lives is termed food-related quality of life (FRQoL).⁵⁷

People with IBS have been shown to have poorer FRQoL than healthy individuals and even individuals with other chronic diseases. In a survey of 80 people with IBS and 95 with IBD,⁵⁸ lower FRQoL scores were reported for people with IBS than for people with IBD59 and compared with historical data for people with asthma and healthy controls,⁵⁸ with symptom severity being a major associated factor. There was an association between greater (multiple) use of therapeutic diets and poorer FRQoL in IBS, although this association was not statistically significant following adjustment for confounders.⁵⁹

Acceptability and FRQoL have rarely been measured in clinical trials of whole-diet interventions. However, in an IBS trial comparing a gluten-free diet with BDA and NICE advice or a low-FODMAP diet,⁴⁰ those randomised to the BDA and NICE diet more commonly reported it was not time consuming to shop for, food labels were adequate to identify suitable foods, and the diet was tasty and enjoyable compared with a gluten-free or low-FODMAP diet. Although there were patterns suggesting higher FRQoL in the BDA or NICE diet group, differences only approached statistical significance (p=0.05, with significance defined as p<0.05) in two domains (“food and meals are positive elements of my life” and “I am generally pleased with my food”).⁴⁰

FRQoL has been measured in some clinical evaluations following whole-diet interventions, with conflicting findings. In a survey of 155 people with IBS in the UK given dietary advice for a low-FODMAP diet, only 87 (56%) agreed that “food and meals are positive elements of my life”.⁵⁴ By contrast, another study in the UK reported no impact of the low-FODMAP diet on FRQoL in people with IBS,⁵⁵ whereas a study in Italy reported FRQoL improved in most patients after the low-FODMAP diet.⁵⁶

Changing eating habits, which might have taken decades to develop, is highly complex, and clinicians should consider, assess, minimise, and mitigate the potential challenges of whole-diet interventions before recommending them for people with IBS. Some practice suggestions for how these challenges should be addressed are provided in panel 1, noting that on many occasions these approaches might require support from a dietitian, although access to specialist dietetic services may vary.

Eating disorders in IBS and association with dietary management

Eating disorders are of relevance to the psychological considerations of dietary management in IBS. Symptoms of eating disorders lie along a spectrum of behavioural, cognitive, and emotional symptoms. Behavioural symptoms include dietary restriction (ie, inadequate energy intake, limited dietary variety, or long periods without eating), binge eating (ie, feeling a sense of loss of eating control while consuming a large amount of food), and compensatory behaviour (eg, self-induced vomiting, laxative misuse, or excessive exercise). Cognitive symptoms might include spending excessive time and mental energy preoccupied by thoughts about eating (eg, obsessive focus on health related to eating or rules about what one should or should not eat) or thoughts about bodyweight or shape; considerable fear regarding eating or specific foods (eg, fear of weight gain or fear of gastrointestinal consequences); or considerable guilt or shame around eating. Some individuals might only experience an effect on quality of life, whereas others might also experience health consequences (eg, considerable weight loss or nutrient deficiencies), some of which may be irreversible (eg, loss of bone mineral density).

Broadly speaking, symptoms are classified into four disorders (Diagnostic and Statistical Manual of Mental Disorders, fifth edition): anorexia nervosa; bulimia nervosa; binge-eating disorder; and avoidant or restrictive food intake disorder (ARFID).⁶⁰ A category of “other specified feeding or eating disorder” is used when symptoms do not meet the full criteria for one of these four disorders. In addition, orthorexia nervosa, an obsessive focus on health related to eating that is not driven by bodyweight or shape concerns, has more recently been described,⁶¹ although there is no consensus on the diagnostic criteria.

There are little available prevalence data on eating disorders in IBS. From the studies that exist in adults with IBS, the prevalence of current possible eating disorder measured using a screening tool was estimated to be between 2% and 29%, whereas lifetime history of diagnosed eating disorder was estimated at 9% and 17%.^62–70 A summary of studies is provided in table 2.

Table 2:

Studies evaluating the rates of eating disorders in adults with IBS

	IBS sample size	Study and sample characteristics	IBS diagnosis	Eating disorder assessment method	Eating disorder prevalence
Guthrie et al (1990)62	152	Cross-sectional study; women only; hospital gastroenterology outpatient clinic in the UK	Abdominal pain and distension, plus altered bowel habits with normal biochemistry and colonoscopy	Eating Attitudes Test (EAT-40) score ≥1063	34 (22%) had a positive screen for a possible eating disorder
Mari et al (2019)64	233	Single-centre prospective study; participants specifically commencing a 6-week low-FODMAP diet; hospital gastroenterology outpatient clinic in the UK	Rome III or Rome IV criteria	SCOFF ≥2 items endorsedindicating possible eating disorder warranting further assessment	54 (23%) had a positive screen for a possible eating disorder
Burton-Murray et al (2020)65	96	Retrospective chart review; consecutive referrals to a hospital neurogastroenterology outpatient clinic in the USA	Physician diagnosis of IBS	Retrospective chart review coding of DSM-5 criteria	28 (29%) with possible ARFID (met some or all of ARFID diagnostic criteria from available chart information)
Burton-Murray et al (2020)66	81	Cross-sectional study; specifically patients referred for anorectal manometry; hospital gastroenterology outpatient clinic in the USA	Rome IV criteria	Eating Attitudes Test-26 score ≥20	16 (20%) with a positive screen for a possible eating disorder
Peat et al (2013)67	427	Cross-sectional; population-based twin study in Sweden	Recurrent abdominal pain that is alleviated after defecation (data were extracted using the definition most closely aligned with Rome III criteria)	Lifetime history of binge eating by Structured Clinical Interview for the DSM-IV	40 (9%) met criteria for lifetime history of binge eating
Porcelli et al (1998)68	64	Cross-sectional study; hospital gastroenterology outpatient clinic in Italy	Rome I Research Diagnostic Questions	Lifetime history of an eating disorder by DSM-IV criteria by unstructured clinical interview	11 (17%) met criteria for an eating disorder (n=5 anorexia nervosa, n=1 bulimia nervosa, and n=5 eating disorder not otherwise specified)
Singh et al (2012)69	184	Cross-sectional study; hospital gastroenterology outpatient clinic located in India	Rome III criteria	Patient Health Questionnaire (unknown cutoffs applied)	3 (2%) with a positive screen for a possible eating disorder (n=1 bulimia nervosa, and n=2 binge-eating disorder)
Yeh et al (2018)70	22 356	Retrospective, population-based study in Taiwan of matched cohorts (IBS vs controls)	IBS ICD-9-CM code 564·1 plus ≥3 gastroenterologist outpatient visits within the previous year	Eating disorder ICD-9-CM codes extracted from clinical psychiatrist encounters (after IBS diagnosis)	5 (0·02%) had a later clinical diagnosis of anorexia nervosa; estimated incidence of anorexia 1·95% per 100 000 person-years

Data are drawn from studies that were reported in two systematic reviews^71,72 found in our literature search. Studies were included in this table if they reported the frequency of eating disorder symptoms in adults with IBS. ARFID=avoidant or restrictive food intake disorder. DSM=Diagnostic and Statistical Manual of Mental Disorders. IBS=irritable bowel syndrome. ICD-9-CM=International Classification of Diseases, Ninth Revision, Clinical Modification. SCOFF=Sick, Control, One stone, Fat, Food.

A population-based study in Taiwan reported that among 22 356 adults clinically diagnosed with IBS, five (0·02%) later received a diagnosis of anorexia nervosa; however, this estimate was limited by the use of clinician-coded International Classification of Diseases, Ninth Revision, Clinical Modification diagnoses.⁷⁰ This study also showed a seven-times increased risk of anorexia nervosa in adults with IBS compared with healthy controls (1·95% per 100 000 person-years vs 0·39% per 100 000 person-years),⁷⁰ although a smaller case–control study in India showed no significant difference in frequency of anorexia nervosa between adults with IBS compared with controls (three [1·6%] of 184 vs two [1·0%] of 198).⁶⁹ Only one study has reported the prevalence of ARFID in adults with IBS but diagnosis was limited to medical chart information.⁶⁵ There is no consensus on the diagnostic criteria for orthorexia nervosa (ie, obsessive focus on health related to eating, not driven by bodyweight or shape concerns)⁶¹ and no studies have reported on its prevalence in IBS. Overall, eating disorders occur in relatively high numbers of people with IBS. It is unclear whether true eating disorder rates are higher for IBS than for the general population (~8%),⁷³ as studies in IBS are limited by methodology—eg, there are no studies using structured clinical diagnosis for eating disorders.

In view of these data, a subset of individuals with IBS seeking dietary management might have previously had, currently have, or be at risk of an eating disorder. Some researchers have hypothesised that whole-diet interventions consisting of extensive dietary restriction in IBS could put some individuals at risk of developing an eating disorder.^74,75 Any such relationship between IBS-related dietary restriction and eating disorders is complex, and might be causal, consequential, or coincidental (figure 2). First, IBS dietary restriction might be a cause of the development of an eating disorder due to intensive focus on food choices (eg, label and menu reading, categorising foods into good and bad, and fearing the consequences of eating bad foods) and food restriction. Second, an existing eating disorder might underlie the drive to follow an IBS-related dietary restriction, and the eating disorder is, therefore, a primary motivator, and dietary restriction is the consequence. Finally, the coexistence of IBS dietary restriction and an eating disorder might be entirely coincidental, whereby the dietary restriction is driven by the desire to manage IBS symptoms.

Figure 2: Dietary restriction in IBS might be causal, consequential, and coincidental to an eating disorder.

Eating disorders are prevalent in IBS and there are concerns regarding a role of IBS-related dietary restriction in their cause. IBS=irritable bowel syndrome.

It is challenging to investigate the relative contribution of IBS dietary restriction as a cause, consequence, or coincidence of eating disorders, and there might be combined contributions in individuals and in populations. To our knowledge, there are no RCTs in IBS measuring both the effect of a restrictive whole-diet intervention and the risk of eating disorder development. However, one observational study of 233 adults with IBS found that those who screened positive for a possible eating disorder (54 [23%] via the Sick, Control, One stone, Fat, Food [SCOFF] screening tool)⁷⁶ before starting group sessions for a low-FODMAP diet had a significantly higher rate of diet adherence at 6-week follow up compared with those who did not screen positive (31 [57%] of 54 vs 64 [36%] of 179).⁶⁴ In another observational study of 31 people with IBS attending group sessions for a low-FODMAP diet, the frequency of positive screens for a possible eating disorder (SCOFF screening tool) did not change from baseline to the end of the restriction phase (seven [23%] of 31 at both time-points), suggesting that the low-FODMAP diet might not increase rates of eating disorders.⁷⁷ However, these studies are limited by short follow-up periods, reliance on a screening tool to detect possible eating disorders that has not been validated in IBS, and information on nutritional status and FRQoL, for which future research is needed.

Despite the lack of data on the temporal nature of eating disorders and IBS dietary management, practitioners should be aware of the potential for development or exacerbation of an eating disorder when considering restrictive whole-diet interventions in people with IBS. Whole-diet interventions, if implemented as intended, are not necessarily the problem. The risk is that a subset of patients could become excessively restrictive beyond the intervention (eg, restrict more foods than required or unable to progress beyond the restriction phase of the low-FODMAP diet). However, there is not yet evidence to identify which patients are at risk or how to mitigate this risk.

We make some clinical practice recommendations, with the caveat that none are, as yet, robustly tested in the integrated care of IBS, and provide links to resources for their implementation (panel 2). An eating disorder diagnosis can only be made by a clinician or with a diagnostic interview. However, health professionals should screen for pre-existing eating disorder symptoms before initiating an intensive dietary restriction and monitor for changes after diet initiation. Eating disorders can be screened by use of the SCOFF questionnaire, with positive responses to two or more items prompting consideration of an eating disorder;⁷⁵ however, a positive screen based on the item “would you say food dominates your life” could over-pathologise patients. ARFID can be screened by use of a nine-item ARFID screen,⁸¹ validated in eating disorders,⁸² but not in IBS. As the SCOFF is validated for non-ARFID eating disorders, we recommend that both a SCOFF questionnaire for eating disorders and an ARFID screening tool are used when feasible. The Fear of Food Questionnaire⁸³ is a newer measure validated in adults with IBS but does not yet have validated screening cutoffs.

In many clinical settings, due to limited resources and appointment times, it is impractical to implement eating disorder screening tools with all patients. Beyond screening tools, measuring actual food intake (via 24-h recall or usual diet history) to evaluate eating patterns and flexibility might be considered. Furthermore, warning signs of disordered eating might include considerable and unintentional weight loss during restrictive whole-diet interventions, detection of which can be facilitated with nutritional screening tools like the Malnutrition Universal Screening⁸⁴). Further detailed recommendations for eating disorder assessment in patients in gastroenterology clinics are available⁷⁸ and some are also provided in panel 2.

When a clinician identifies a patient with a possible eating disorder, referral to eating disorder specialists should be considered. We acknowledge that access to evidence-based eating disorder care can be challenging, with complex systemic and structural barriers. For example, within public health-care systems there might be long waiting lists for community eating disorder services (eg, England and Scotland),⁸⁵ whereas in private health-care systems financial barriers among patients have been reported (eg, in the USA).⁸⁶ Even when care is received, not all clinicians or programmes engage in evidence-based practice.⁸⁷ We encourage gastroenterology clinicians to identify local referral options in their communities, as not referring a patient for further evaluation could decrease the chance that the patient ever receives eating disorder care.⁸⁸ When a dietary approach is considered in patients with IBS and a possible eating disorder, approaches to consider include supplements (eg, probiotics or fibre supplements) and whole-diet interventions that are not excessively restrictive such as BDA or NICE dietary advice, the Mediterranean diet,²⁴ or a FODMAP-light approach.³⁴

Delivering IBS dietary management in practice

Selecting, counselling, and monitoring a patient with IBS who is embarking on dietary management requires consideration of a complex array of factors, including clinical effectiveness, targeting the symptom most burdensome, and personalising the intervention to minimise and mitigate the challenges discussed. Dietary intervention can be initiated and managed by the patient themselves, by a health professional (either a non-dietitian or a dietitian), or in an integrated care environment.

Patient-initiated and self-managed dietary management in IBS

People with IBS regularly self-manage their own condition, either in the absence of a diagnosis or following discharge from physician management in primary or secondary care. Self-management is an important component of chronic disease care and emphasises the role of the patient in managing their own health. Self-management is important in IBS due to the high prevalence and chronicity of symptoms.

Self-management using supplements is common in IBS. At least 14·8% of people with IBS used herbal supplements in the USA in a survey of more than 1000 patients from primary and secondary care. Nutrient supplements (eg, magnesium)⁸⁸ and microbiome-targeted supplements, such as probiotics, are also popular.⁹⁰ Many people who use supplements for their IBS start supplements without support.

Self-management of whole-diet interventions can be more challenging as they can be inherently more complex to understand, implement, and maintain. Less complex whole-diet interventions, such as the BDA or NICE diet, can be undertaken through self-management using online resources (panel 2), with or without support from a health-care professional.

Several studies have evaluated the success of self-management of more complex whole-diet interventions in IBS. In a Canadian survey of 80 patients with functional gastrointestinal symptoms recommended a low-FODMAP diet, fewer patients achieved the therapeutic FODMAP target if they were not supported by a dietitian (37 [31%]) compared with those receiving dietetic support.⁹¹ Similarly, many individuals report barriers to self-management with a gluten-free diet. Although not in IBS, 215 (22%) of 978 individuals with coeliac disease cited non-referral to a dietitian as a barrier to adherence to a gluten-free diet, and odds for non-adherence were higher in those not counselled by a dietitian compared with those that were.⁹²

Many resources are available to support people with IBS following a whole-diet intervention, but few have been evaluated formally for efficacy. In a small study of a novel artificial intelligence mobile app to support the low-FODMAP diet, 14 people with IBS reported a greater improvement in quality of life with the app compared with the 11 people with IBS assigned to standard education.⁹³ In another study of people with self-reported gut symptoms, including IBS, mobile app-supported self-management of the low-FODMAP diet resulted in reductions in the rates of abdominal pain and bloating in analyses of over 8000 and 11 000 users reporting these symptoms, respectively.⁹⁴ In a feasibility RCT of 51 people with functional bowel disorders in the UK, although a mobile app and written information reduced symptoms in some people, written advice was less efficacious than one-to-one dietary advice from a dietitian but there was no difference in symptom response between mobile app and dietitian advice groups.⁹⁵ It is possible that mobile apps in conjunction with support from health-care professionals will elicit higher engagement and greater effectiveness than self-management alone.

Self-management of whole-diet interventions might be possible in IBS, especially with supportive resources (eg, apps, diet sheets, or recipe books), but there are few high-quality trials to measure efficacy, impact on diet quality, or safety. Understanding who is most amenable to self-management would represent a considerable advance in better targeting those who are most likely to need, or not need, professional support.

Health professional (non-dietitian) management of whole-diet interventions in IBS

Physicians in primary care and secondary care might have poor access to local dietetic services and, therefore, might not refer patients with IBS to dietitians. Many gastroenterologists provide dietary advice to patients, but the duration of this advice during a consultation can be short.⁹⁶ In an uncontrolled 6-week study in IBS, low-FODMAP dietary advice delivered by a gastroenterologist of a duration of 20–30 min resulted in improved symptoms; however, only 51% (18 of 35) reported regular adherence and most cited the diet’s complexity as the reason for non-adherence.⁹⁷ A qualitative study of semi-structured interviews in eight people with IBS who were on a low-FODMAP diet as their primary treatment reported that patients receiving low-FODMAP dietary advice from their general practitioner or gastroenterologist found the advice to be overly simplistic and lacking individualisation and practicality.⁹⁸

Guidelines from the UK,⁹⁹ the USA,¹⁰⁰ and Canada¹⁰¹ recommend dietetic supervision of patients undertaking a low-FODMAP diet. This supervision is to enable personalisation and prevent over-restriction, which is associated with concerns such as undernutrition, impaired FRQoL, and psychological risk.⁷⁴

Dietitian management of whole-diet interventions in IBS

Most supplement interventions are undertaken using self-management, either over-the-counter or prescription, with or without the support of a health professional, whereas almost all research on whole-diet interventions is delivered by a dietitian. Dietitians are qualified, and in many countries regulated, health professionals that assess, diagnose, and treat diet and nutritional problems in individuals and populations.

In systematic reviews of two whole-diet interventions in IBS, of the clinical trials that were delivered through dietary counselling, 11 of 12 of the low-FODMAP diet¹¹ and both trials of the gluten-free diet delivered the intervention via a dietitian.¹² In a three-arm trial of the BDA and NICE diet, low-FODMAP diet, and gluten-free diet in IBS,⁴⁰ all patients received counselling from a dietitian, and a study of 51 patients with IBS found that dietitian-managed care improved outcomes compared with mobile app-based or written support, although differences versus the app were not statistically significant.⁹⁵

In addition to RCTs, real-world clinical evaluations of dietitian delivery of whole-diet interventions have been conducted. For example, in a Canadian case-series of 80 patients with functional gastrointestinal symptoms recommended a low-FODMAP diet, those who received counselling from a dietitian had a lower intake of FODMAPs, were more likely to achieve a FODMAP intake less than the therapeutic threshold, and reported greater understanding of dietary instructions than those who received instruction from a gastroenterologist, general practitioner, or internet sites.⁹¹

Despite extensive clinical trial and real-world evidence of the clinical effectiveness of dietitians in delivering whole-diet interventions in IBS, experience in practice is that access to specialist counselling from a dietitian is limited due to long waiting lists, cost, and insurance coverage in some private health-care systems. In a survey of gastroenterologists in the USA, 91% (247 of 272) believed that the use of a gastroenterology-specialist dietitian improved effectiveness of managing IBS symptoms, yet 78% (211 of 272) indicated that the lack of insurance coverage was a major barrier to referring patients.⁹⁶ A survey in England reported that although 96% (118 of 123) of National Health Service Trusts provided general dietetic services for IBS, only approximately half (49% [60 of 123]) had a dietitian specifically responsible for the delivery of dietary management for IBS, with wide variations in waiting lists for patients.¹⁰² These demands for, and variations in supply of, dietetic services have led to innovative ways for patients to access dietetic advice for IBS, including via group and online education.

Group education from a dietitian has been used to deliver low-FODMAP dietary counselling. In a study of 55 patients with IBS, group education delivered by a specialist dietitian in two 90-min group sessions resulted in over half 54% (27 of 55) of those completing the study reporting symptomatic responses.¹⁰³ In a study of 364 patients with IBS, the proportion of symptom responders (54% [142 of 263] vs 60% [61 of 101]) at follow-up was no different after 90-min group education delivered by a specialist dietitian to 263 versus one-to-one dietetic counselling delivered to 101.104 Health-care costs were lower for group education (£67 per patient) than for one-to-one counselling (£139 per patient) for the same clinical benefit.¹⁰⁴ Group education could be a cost-saving intervention but could also enable longer duration of exposure to a specialist dietitian, enhance learning via group education theory, collaborative facilitation, and peer support, and provide equal outcomes. There are currently no RCTs comparing group and one-to-one consultations for whole-diet interventions in IBS.¹⁰⁵

Webinars are online presentations that are either recorded or presented live. Live webinars allow for inter-active content. Webinars of BDA and NICE dietary advice by dietitians (panel 2) have led to high levels of satisfaction and a reduction in demand for one-to-one specialist dietitian consultations.¹⁰⁶ Webinars given by dietitians around the low-FODMAP diet (panel 2) have resulted in a majority of patients reporting adherence to the diet, increases from baseline in the number with adequate relief of IBS symptoms, and reductions in all individual symptoms.¹⁰⁷ Such webinars and other online tools might be used alone as part of self-management or in conjunction with support from a dietitian.

Combined and integrated care approaches to dietary management of IBS

In addition to the dietary management of IBS, there is considerable evidence for non-dietary approaches.^5,6 The British Society of Gastroenterology guidelines for IBS recommend commencing with diet and lifestyle advice and, when these are unsuccessful, moving to first-line and then second-line drugs, followed by gut–brain behavioural therapies.⁹⁹ A discrete choice experiment in 185 people with IBS supports this approach, with the most preferred treatment being diet (48% of occasions), followed by pharmacological (29%) and gut–brain behavioural therapies (23%).⁷ In reality, many patients undertaking dietary management for IBS will receive concomitant pharmacological (over the counter or prescription) or gut–brain behavioural (self-directed or clinician-managed) therapies.¹⁰⁸ However, there are few studies investigating dietary management specifically in combination with pharmacological or gut–brain behavioural therapy. Of note, many clinical trials of dietary management in IBS have been performed in mixed populations of patients, some of whom were already using pharmacological or gut–brain behavioural therapy.^27,29,31,40 In one trial comparing the tricyclic antidepressant amitriptyline with placebo in the second-line treatment of IBS, which found efficacy of the drug over placebo, both groups were also provided with an information sheet regarding the BDA and NICE diet.¹⁰⁹ It is recommended that multidisciplinary care is provided to patients with IBS where possible,¹⁰⁸ and more research is needed to understand for whom, when, and in what combination treatments should be delivered.

In view of the varied management options both within and between patients with IBS, studies have investigated the benefit of patients being managed in an integrated care model with access to wide multidisciplinary expertise, including dietitians and psychologists. An RCT in 188 patients with disorders of gut–brain interaction compared standard gastroenterologist-only management with a multidisciplinary care model including gastroenterologists, dietitians, gut-focused hypnotherapists, psychiatrists, and physiotherapists.¹¹⁰ Overall, more participants assigned to the multidisciplinary model than assigned to standard care had global symptom improvement before clinic discharge (82 [84%] of 98 vs 26 [57%] of 46; risk ratio 1·50 [95% CI 1·13–1·93]; p=0·00045). Of the 85 patients with IBS, more patients participating in multidisciplinary versus standard care reported global symptom improvement (50 [85%] of 59 vs 17 [65%] of 26; p=0·044) and more had a clinically important reduction (≥50 points) in IBS Symptom Severity Scale (IBS-SSS; 39 [66%] vs ten [38%]; p=0·017).¹¹⁰ The significant difference in numbers achieving a reduction of 50 points or more in IBS-SSS was maintained during long-term follow-up at 1 year.¹¹¹

Identifying responders to diet interventions in IBS

In view of the potential risks of restrictive whole-diet interventions, the potential to identify those most likely to have clinical benefit would enable targeted dietary advice. However, predictors of response to supplements, foods, or whole-diet interventions for IBS remain elusive. In terms of clinical phenotype, in an RCT of wheat bran in people with all IBS subtypes, only the presence of constipation at baseline predicted response to bran.¹¹² Restriction and then double-blind challenge should, in theory, predict who will respond to withdrawal of particular dietary constituents; however, patients with IBS might not exhibit symptom improvement specific to the withdrawal of the dietary component suspected to be implicated,^113–115 suggesting some of the effect is anticipatory.

In one study based on data from a trial of the BDA and NICE diet versus a low-FODMAP diet in participants with IBS, higher energy intake, lower symptom scores, and lower dysbiosis index at baseline predicted improvement in abdominal pain to both diets, whereas higher baseline oligosaccharide intake predicted response to the BDA and NICE dietary advice.¹¹⁶ Using data from the same trial, response to a low-FODMAP diet was predicted by both faecal bacterial profile and severity of dysbiosis at baseline.¹¹⁷ By contrast, in post-hoc analyses of data from another IBS RCT, baseline faecal microbiota composition was a poor predictor of response to a low-FODMAP diet,¹¹⁸ whereas volatile organic compound profiles classified responders with 97% accuracy.¹¹⁹ In an observational study, two distinct microbial profiles (pathogenic-like and health-like) were identified in people with IBS and a 4-week, open-label, low-FODMAP diet led to maintenance of the health-like microbial profile, whereas the pathogenic-like profile shifted to resemble the health-like profile.¹²⁰ There was a significantly greater decrease from baseline in global symptom scores in those with the pathogenic profile versus those with the health-like profile.¹²⁰ Others have shown that the genetic profile, and thus the potential functional capacity, of the microbiome of responders to a low-FODMAP diet is different, characterised by higher abundance of genes relating to methane and fatty acid metabolism¹²¹ or higher faecal and urinary metabolites at baseline, such as higher faecal propionate and cyclohexanecarboxylic acid.¹²² In terms of predictors of response to a gluten-free diet in IBS, HLA-DQ2 expression and coeliac disease-associated serum IgG antibodies have been proposed.¹²³ Although personalised nutrition offers great potential, methods for identifying patients with IBS most likely to respond to dietary management are at an exploratory stage and cannot yet be easily implemented in clinical practice.

Conclusions

Diet is a cornerstone of IBS management, and will continue to be as long as patients are interested in what they eat and how it impacts their symptoms. There are many research gaps to fill, including limited research on food supplements and food interventions in IBS, the optimal methods of delivery of restrictive whole-diet interventions, and the efficacy of non-restrictive whole-diet interventions (eg, BDA or NICE, high-fibre, or Mediterranean diets). Clinicians should be aware of the many internal and external factors that influence eating behaviours and incorporate them into their assessment of patients before recommending dietary management. Inappropriate whole-diet interventions or inadequate monitoring can risk patient safety through poor nutrient intake and the possible risk of exacerbation or development of an eating disorder, and can impact FRQoL. To further improve dietetic care for people with IBS, we need improved understanding of the dietary interventions that might benefit patients, which patients they might benefit, and how these interventions can be delivered safely and effectively.

Panel 1: Practice suggestions in addressing challenges of dietary management in irritable bowel syndrome (IBS).

Challenge 1: Personalising dietary management to the patient

• Ask patients about the factors that influence their food choices (eg, sex or gender, culture, religion, ethnicity, cost, and food availability) and consider how these factors will influence dietary management

• Train in, and practice, cultural competence

• Develop an understanding of foods consumed by minority ethnic groups relevant to the local population and learn about their content, which can include triggers of IBS symptoms (eg, fermentable oligosaccharides, disaccharides, monosaccharides, and polyols [FODMAPs] or gluten)

• Use jargon-free dietary information (verbal, written, and online) relevant to the health literacy of the patient

• Refer the patient to a specialist dietitian who can provide expert dietary counselling that personalises dietary management

Challenge 2: Cost and availability of supplements, foods, and whole diets

• Understand the cost of food supplements and which brands are cheapest and from where they can be obtained

• Learn which supplements are available on prescription (if any)

• Recommend outlets that sell lower-priced alternative foods (ie, gluten-free or lactose-free)

• Consider that large supermarkets might be cheaper than smaller shops or supermarkets

• Use discount retailers—either online or in store—where specialty products might be available

• Review special offers, such as buy one get one free

• Recommend bulk-buying discounted items, assuming good shelf life and home storage

• Instead of more costly wheat-free or gluten-free pasta or breads, recommend lower-cost grains (eg, rice or corn) or other sources of complex carbohydrates (eg, potatoes)

• Suggest baking wheat-free or gluten-free breads, cakes, and biscuits with basic ingredients rather than buying ready-made versions

Challenge 3: Impact of restrictive whole-diet interventions on food-related quality of life

• Consider less stringent whole-diet interventions (eg, the British Dietetic Association or National Institute for Health and Care Excellence diet or FODMAP-light diet) or supplement or food interventions

• Limit dietary restriction only to that necessary for adequate symptom control

• Explain that an episodic lapse in diet to accommodate a social event will not cause damage to the gut

• Reassure patients that when eating out, limiting only major diet triggers might be sufficient

• Provide comprehensive resources listing suitable restaurant meals for various cuisines

• If a patient reports considerable anxiety or rigidity about eating out, eating with others, or making daily food choices, consider diet approaches to facilitate flexibility and screening for possible eating disorders

Challenge 4: Providing support and resources specific to the patient

• Dietitians are evidence-based experts in supplements and food and whole-diet interventions, and should be used when resources allow

• Specialist clinician follow-up should be done, as necessary

• Research the quality, availability, and cost of relevant apps, books, and online courses

Panel 2: Suggested resources to screen and support patients when considering dietary management in irritable bowel syndrome (IBS).

Many screening tools are not yet validated in IBS-specific samples; thus, the validity of scores and the screening cutoffs should be used with caution. Individual items could be selected to guide clinician-directed questioning. Please note some resources might require a licence before use

Eating disorder screening (indicating possible eating disorder)

Sick, Control, One stone, Fat, Food screening tool (known as SCOFF; verbal or survey screener)⁷⁶

Nine-item avoidant or restrictive food intake disorder screen (survey screener)

Cutoff scores for adults are currently: 10 or more on the Picky Eating scale (items 1, 2, and 3); 9 or more on the Appetite scale (items 4, 5, and 6); or 10 or more on the Fear scale (items 7, 8, and 9)⁷⁸

Eating Disorder Examination-Questionnaire (survey screener)

Cutoff score is 4·0 or more on the Global Score and shortform options are available (https://www.credo-1oxford.com/pdfs/EDE-Q_6.0.pdf)⁷⁹

Eating disorder practice guidelines

Academy for Eating Disorders Medical Care Standards guidelines (https://www.aedweb.org/resources/publications/medical-care-standards)

National Health Service UK eating disorder guidelines (https://www.england.nhs.uk/wp-content/uploads/2019/08/aed-guidance.pdf)

American Psychiatric Association eating disorder guidelines (https://psychiatryonline.org/doi/book/10.1176/appi.books.9780890424865)

Screening for nutrient intake

Block questionnaire for fibre, fruit, and vegetable intake (https://www.nutritionquest.com/wellness/free-assessment-tools-for-individuals/fruit-vegetable-fiber-screener/)⁸⁰

Resources for dietary education

• Webinars on British Dietetic Association (BDA) and National Institute for Health and Care Excellence (NICE) dietary advice and a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs; https://patientwebinars.co.uk/condition/ibs/webinars/)

• Information about the BDA (or NICE) diet (https://www.bda.uk.com/resource/irritable-bowel-syndrome-diet.Html )

• Information about the low-FODMAP diet (https://www.monashfodmap.com/ibs-central/i-have-ibs/starting-the-low-fodmap-diet/ and https://mynutriweb.com/key-resources-the-low-fodmap-diet-in-ibs/)

Patient support groups

https://gi.org/topics/irritable-bowel-syndrome/

https://aboutibs.org/

https://gutscharity.org.uk/

Search strategy and selection criteria.

References for this Review were identified through searches of PubMed with the search terms “irritable bowel syndrome”, “diet”, “nutrition”, ”challenges”, ”education”, ”psychology”, and ”eating and feeding disorder”, and combinations thereof, from database inception to May 8, 2024. English articles (abstracts were not excluded) most relevant to the Review and to current clinical practice were prioritised. Additional articles were identified through searches of the authors’ own files. The final reference list was generated on the basis of relevance to the broad scope of this Review, and based on study originality and rigour, with the understanding that evidence for clinical efficacy can come from multiple quality clinical trials, whereas evidence of application to practice might be from lower quality studies, and therefore the best available evidence was used where possible. When insufficient studies were available, the combined expertise of the authors was used to comment on challenges and solutions in clinical practice.