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Evidence-based and mechanistic insights into exclusion diets for IBS

Abstract

Exclusion diets are becoming increasingly popular in the management of irritable bowel syndrome (IBS). Several mechanisms exist by which food items might cause gastrointestinal symptoms, such as direct osmotic effects of food in the gut lumen, changes to the gut microbiota and immune activation. These effects have been demonstrated in animal models and in human studies, particularly in the case of gluten-free diets and diets low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs). Indeed, randomized controlled trials (RCTs) suggest that gluten-free diets and low-FODMAP diets improve IBS symptoms, and guidelines recommend the latter approach for treating symptoms in some patients with IBS. Designing such RCTs is challenging as participants need to eat so an ‘inert’ placebo is not an option. Blinding is also an issue with these studies; in the future, new exclusion diets should not advertise what the diet consists of until it is proved to reduce symptoms. In this Review, we outline the advantages and disadvantages of each choice of control group and emphasize the importance of collecting mechanistic data (regarding direct effects of food on the gut lumen, changes in gut microbiota and intestinal inflammation) as well as symptom data in RCTs of exclusion diets in IBS.

Key points

  • Interest in exclusion diets to treat irritable bowel syndrome (IBS) is resurging.

  • Randomized controlled trials (RCTs) have shown that some diets — such as a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols or a gluten-free diet — might reduce IBS symptoms.

  • Diet might have an effect on IBS symptoms through various mechanisms, such as a direct effect of food, changing gut microbiota and immune activation.

  • RCTs evaluating exclusion diets have unique issues relating to the choice of controls, which makes interpretation of the results challenging.

  • Future RCTs should collect data that provide mechanistic insights into how the diet might be exerting effects on symptoms.

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Fig. 1: Mechanisms by which FODMAPs might cause IBS symptoms.
Fig. 2: Mechanisms by which wheat might cause IBS symptoms.

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Acknowledgements

The work of P.M. and P.B. is funded by Canadian Institutes of Health Research (CIHR) (RN279389-358033). The Inflammation, Microbiome, and Alimentation: Gastro-Intestinal and Neuropsychiatric Effects: the IMAGINE network — a Strategy for Patient-Oriented Research CIHR Chronic Disease Network.

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Moayyedi, P., Simrén, M. & Bercik, P. Evidence-based and mechanistic insights into exclusion diets for IBS. Nat Rev Gastroenterol Hepatol 17, 406–413 (2020). https://doi.org/10.1038/s41575-020-0270-3

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