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The low FODMAP diet in the management of irritable bowel syndrome: an evidence-based review of FODMAP restriction, reintroduction and personalisation in clinical practice.

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Whelan K, Martin LD, Staudacher H et al. Journal of Human Nutrition & Dietetics 2018 Apr 31(2):239-255.

Irritable bowel syndrome (IBS) is a debilitating functional gastrointestinal disorder. As dietary triggers are reported to be central to symptom generation in up to 84% of patients with IBS, dietary modification is increasingly employed to help manage symptoms. 

A low FODMAP diet for the management of functional gut symptoms in IBS has been shown to be efficacious with a clinical response rate in 50-80% of IBS patients. The aim of this review was to provide practical guidance on patient assessment and implementation and monitoring of the low FODMAP diet.

 

Assessment and monitoring of dietary inventions in IBS

There is currently no diagnostic biomarker for IBS and symptoms can overlap with other organic disease. Routine investigations should be undertaken to exclude organic causes of disease such as coeliac disease, inflammatory bowel disease and gastrointestinal cancer. As a result, IBS is often a diagnosis of exclusion, which can be unsatisfactory from a patient perspective. Therefore, a positive diagnosis should be emphasised. The recently revised ROME IV criteria should be used by the referring clinician to identify the type of functional disorder (e.g. IBS, functional bloating) and the IBS subtype should be recorded as this may be useful in tailoring dietary advice. Assessment of lifestyle factors such as stress, social history and physical activity, use of IBS medication and other treatments, and any known food allergies or intolerances and associated testing that has been undertaken is important to note.

A variety of tools to measure baseline symptoms and to monitor response to dietary intervention is available for use in IBS. These include an IBS modified version of the Gastrointestinal Symptom Rating Scale (GSRS-IBS), the IBS Severity Scoring System (IBS-SSS), the Bristol Stool Form Scale and quality of life measures such as the Short Form 36 Health Survey (SF-36) and the IBS Quality of Life (IBS-QOL) questionnaire. Qualitative and quantitative dietary assessment methods should be utilised as standard with additional investigation focused on identification of foods perceived to be induce symptoms, current dietary restrictions and the use of nutritional supplements, probiotics and prebiotics as well as complementary/alternative medicines.

 

Low FODMAP diet: implementing the intervention

The low FODMAP diet consists of three distinct stages that take place across two to three clinical appointments: restriction; reintroduction; and personalisation. The initial appointment can consist of a detailed assessment and an explanation of the effects of FODMAPs followed by tailored dietary advice regarding FODMAP restriction. Available resources to support the comprehensive dietary counselling include diet sheets, smartphone applications, cookbooks and online resources. Food label reading is a key part of the counselling for a low FOMAP diet although smartphone applications, and low FODMAP certification logos on product packaging, can also assist with this.
It is important to explain certain nuances of the low FODMAP diet. An example is that whilst the fructan content of wheat is relatively low because it is consumed in large quantities (e.g. in bread or pasta), it contributes the largest amount of fructans to the UK diet. The practical implication of this is that foods containing wheat as a major ingredient should be excluded whereas foods containing it as a minor ingredient (e.g. sauces with wheat starch thickener) do not need to be excluded. This helps to avoid unnecessary food restriction. Barriers to dietary adherence also need to be addressed including the perceptions regarding low palatability of some specialist food products, cost as well as limitations when eating out.

Randomised controlled trials (RCTs) of strict FODMAP restriction have lasted up to 6 weeks and have shown changes in  gastrointestinal microbiota and possibly nutritional adequacy. Therefore, in practice, 4 weeks is recommended as this provides sufficient time (in most cases) to achieve symptom improvement. However, clinical capacity and patient choice may extend this. Patients should be advised to spend time planning implementation of the low FODMAP diet into their lifestyle.
In some cases, restriction of lactose and/or fructose may not be warranted if they are not suspected of symptom induction. Breath tests for lactose, fructose or polyol malabsorption are no longer indicated as false positives/negatives are common and there is poor correlation between malabsorption and intolerance. Furthermore, these only measure colonic fermentation products and do not take account of the effect of FODMAPs on small intestinal water. In some instances, strict FODMAP restriction may not be appropriate (e.g. a patient’s ability to understand and adhere, significant dietary restrictions), and dietitians needs to exercise clinical judgement to implement a partial low FODMAP diet. However, there are no quality research studies to support a partial low FODMAP diet.

 

FODMAP Reintroduction (short-term follow up)

This is a series of staged, dosed FODMAP challenges to assess tolerance with the aim of improving longer-term dietary variety and nutritional adequacy. Whilst very little evidence exists to inform dietetic practice for this stage of the diet it is good practice to follow-up all patients and prevent long-term FODMAP restriction due to the impact on gastrointestinal microbiota and nutrient intake. A shorter consultation, 4-12 weeks after the initial appointment, is the most widely used approach. Anthropometric measurements should be checked, particularly weight as small amounts of weight loss have been reported during the restriction phase. Clinical assessment should help to determine the success of the intervention and allow the dietitian to determine whether continued restriction is required or not. Dietary assessment should check adherence and assessment of nutritional adequacy with a focus on specific nutrients shown to be at risk on a low FODMAP diet e.g. fibre, calcium, iron. It is also important to discuss the acceptability of a low FODMAP diet in terms of availability, cost and impact on lifestyle.

A variability in tolerance to different FODMAPs, as well as between individuals and within the same individual over time should also be explained at follow-up. Limited research exists on the optimal number and order of foods to reintroduce. In practice, this is determined based on the clinical situation and dietary preferences. The wide variation in impact of individual FODMAPs on symptoms is likely to be affected by a number of other factors including total FODMAP load at a meal, other food components within a meal (e.g. fat, fibre), gastrointestinal transit time, visceral hypersensitivity and microbiota. Lifestyle and stress are also important contributors to IBS symptoms in general and may contribute to individual variation in symptom exacerbation with the same individual at different times. Reassurance that high FODMAP foods are unlikely to have negative effects beyond symptom induction may be important to discuss at follow up, especially if a low FODMAP diet has resulted in negatively affecting quality of life.

 

FODMAP Personalisation (long-term follow up)

This stage focuses on increasing dietary variety and nutritional adequacy whilst maintaining symptom control. In most cases, patients can manage this stage without a dietetic consultation but in some instances a third appointment may be warranted. As near to ‘normal’ a diet should be encouraged with a strong focus on healthy-eating advice with a minimal impact on the psychosocial aspects of a patient’s life in relation to food e.g. eating out. Limited evidence exists for the efficacy of a modified FODMAP diet, however, one study reported 57% of patients experienced adequate symptom relief on this stage of the diet, with 70% of patients who reported adequate symptom relief on the initial stage of the low FODMAP diet reporting sustained benefit on a modified FODMAP diet.

 

Specific Considerations

Inadequate symptom response
Approximately 50-80% of patients with IBS experience symptom relief following restriction of FODMAPs. Therefore, 20-50% do not. This may be because of poor adherence and can be addressed at follow-up. If the patient wishes to retry FODMAP restriction then any barriers to adherence should be addressed and further follow-up provided. For those who strictly adhered to a low FODMAP diet yet did not experience symptom relief then FODMAP restriction should be ceased and careful reintroduction of FODMAPs commenced. Research is underway with the aim of identifying markers that predict response to FODMAP restriction.

Other dietary approaches can be trialled in non-responders including probiotic supplementation. In addition, supplemental dietary fibre, in particular ispaghula/psyllium, may provide overall IBS symptom relief. A final consideration to explain the lack of non-response to FODMAP restriction is that the symptoms are as a result of, at least in part, non-coeliac gluten sensitivity (NCGS). Therefore, in patients where there is clinical suspicion of NCGS, preliminary research suggests that a gluten-free diet may be trialled with some success. It is also important to remember that dietary intervention may not be indicated in some patients as other factors such as stress may have a greater impact on symptoms than diet. In these cases, referral back to the referring clinician is recommended.

Nutritional Adequacy
Few studies have investigated the effect of the low FODMAP diet on nutritional adequacy. One study demonstrated a broadly similar micronutrient intake on a low FODMAP diet when compared with a habitual diet with the exception of lower calcium intakes. Another study showed a greater degree of restriction in patients who had received no dietary counselling and this group had significantly lower calcium intakes. Excessive avoidance of dairy and inadequate replacement of dairy sources of calcium may impair calcium intake on a low FODMAP diet. There is also a significant change in intake of carbohydrate sources on a low FODMAP diet, which might impact fibre intake. Patients should be advised to follow national guidance on the intake of fruit and vegetables unless other medical issues contraindicate this. Specific advice on high-fibre, low-FODMAP carbohydrate sources should be provided.

Constipation
There is a reduction in small intestinal water on a low FODMAP diet and this has resulted in concerns of the intervention exacerbating constipation in IBS patients. However, there is limited evidence that a low FODMAP diet may actually be effective for IBS-constipation. Ensuring appropriate fibre sources or fibre supplementation with rice or oat bran or linseeds may be appropriate. In addition, meta-analyses have shown that some probiotic strains are effective in managing constipation specifically and IBS symptoms in general.

Changes to the gastrointestinal microbiota
It is acknowledged that the low FODMAP diet affects the gastrointestinal microbiota. A reduced intake of prebiotics whilst on a low FODMAP diet is presumed, at least in part, to be a cause of this change. It is unknown whether these effects persist following FODMAP reintroduction in the longer term; they are related to symptom improvement nor whether these reductions in microbiota have any impact on colonic health. A RCT demonstrated the a probiotic taken in conjunction with a low FODMAP diet was able to partially prevent some of the microbiota changes occurring, however, further research is needed.

Delivering an effective dietetic service
With increasing demand for use of the low FODMAP diet to help manage IBS symptoms but only a limited supply of FODMAP-trained dietitians, alternative ways to deliver education around this intervention are being sought such as group education sessions. Alternatively, web-based symptom measurement alongside dietitian-led low FODMAP advice has been tested and shown to improve symptoms compared to probiotics or no intervention.
In conclusion, there are still many unanswered questions regarding the long-term effects of a low FODMAP diet and educational methods that may be useful to help achieve symptom control. Further high-quality research in these areas is required.

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