Review Article

Biological Mechanisms for Symptom Causation by Individual FODMAP Subgroups

The Case for a More Personalised Approach to Dietary Restriction

Xiao Jing Wang; Michael Camilleri; Stephen Vanner; Caroline Tuck

Disclosures

Aliment Pharmacol Ther. 2019;50(5):517-529. 

In This Article

Abstract and Introduction

Abstract

Background: Due to the paucity of targeted therapy for irritable bowel syndrome (IBS), many patients turn to dietary modifications for symptom management. The combination of five subgroups of poorly absorbed and rapidly fermented carbohydrates—fructans, galacto-oligosaccharides, lactose, excess fructose and polyols—are thought to trigger gastrointestinal symptoms and are referred to collectively as "FODMAPs".

Aims: To examine the biological plausibility and mechanisms by which foods high in specific FODMAP subgroups cause symptoms, and to use this information to explore the possibility of targeting select dietary components to allow for a more personalised approach to dietary adjustment

Methods: Recent literature was analysed via search databases including Medline, PubMed and Scopus.

Results: Lactose, fructans and galacto-oligosaccharides have strong biologic plausibility for symptom generation due to lack of hydrolases resulting in distention from osmosis and rapid fermentation. However, excess fructose and polyols may only cause symptoms in specific individuals when consumed in high doses, but this remains to be established. There is evidence to suggest that certain patient characteristics such as ethnicity may predict response to lactose, but differentiation of other subgroups is difficult prior to dietary manipulation.

Conclusions: While some clear mechanisms of action for symptom generation have been established, further research is needed to understand which patients will respond to specific FODMAP subgroup restriction. We suggest that clinicians consider in some patients a tailored, personalised "bottom-up" approach to the low-FODMAP diet, such as dietary restriction relevant to the patients' ethnicity, symptom profile and usual dietary intake.

Introduction

Due to the paucity of targeted therapy for irritable bowel syndrome (IBS), many patients turn to dietary modifications for management of symptoms.[1] The combination of five subgroups of specific poorly absorbed and rapidly fermented carbohydrates—fructans, galacto-oligosaccharides, lactose, excess fructose and polyols—are thought to trigger gastrointestinal symptoms and are referred to by the collective term "FODMAP" (Table 1). The low-FODMAP diet is not the first dietary intervention proposed for IBS and it faces the same challenges as previously proposed interventions in efficacy testing including lack of standardisation of both control and intervention diets across studies, assessment of pre-trial food intolerances, and lack of data on adherence to the diet during the trial. While there have been randomised controlled trials suggesting global symptom improvement with the low-FODMAP (fermentable, oligo-, di-, mono-saccharides and polyols) diet,[2,3] other controlled trials as well as systematic review and meta-analyses have not shown consistent efficacy over control diets, gut directed hypnotherapy or yoga, although these studies suffer from varying severity of design flaws (Table 2 and Table 3). Despite this, the diet is commonly recommended by physicians and allied healthcare professionals to patients with IBS, inflammatory bowel disease (IBD) where functional symptoms continue in remission, and other conditions such as functional bloating. The authoritative National Institute for Health and Care Excellence (NICE) of the United Kingdom recommended in an addendum to NICE guideline CG61 regarding management of irritable bowel syndrome in adults: "If a person's IBS symptoms persist while following general lifestyle and dietary advice, offer advice on further dietary management. Such advice should: include single food avoidance and exclusion diets (eg a low-FODMAP diet)".[4] With the evidence published since that guideline written in 2015, there is an opportunity to explore evidence-based strategies for a personalised approach to dietary carbohydrate restrictions.

The low-FODMAP diet is designed to include three phases: an initial restriction phase where high-FODMAP foods are avoided for 2–8 weeks, a re-challenge phase, and finally a long-term maintenance phase.[5] While dietitian-taught therapy is believed to be associated with success of the diet, poor access to dietitians may impact patients' ability to receive individualised dietary guidance.[5]

Our objective is not to review the evidence of overall or specific efficacy of the low-FODMAP diet. Rather, based on available evidence, we present an overview of the plausible biological mechanisms behind symptom generation from the low-FODMAP diet and propose a hypothesis for ways in which the evidence can be tailored to the individual patient (eg prior dietary intolerance, likelihood of intolerance or malabsorption based on ethnicity or race), guided by the opportunity to explore single food avoidance in accordance with the NICE guideline where appropriate.

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