The low FODMAP diet for IBS: A multicentre UK study assessing long-term follow-up

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Diet appears to be a key trigger for IBS symptoms with food-related symptoms reported in 60-80% of individuals. Over the last decade there has been a significant increase in interest in dietary therapies including increasing evidence for the use of a low fermentable oligo-, di-, mono-saccharides and polyols (FODMAP) diet to help manage IBS symptoms. At present, the majority of studies have assessed efficacy of a low FODMAP diet (LFD) in the short term with only one assessing nutritional and FODMAP intake in the long term. The aim of this study was to assess the efficacy of the low FODMAP diet at long-term follow-up, assess changes to nutritional and FODMAP composition at long-term follow-up in addition to effect on socialising.

 

Patients with IBS who had received low FODMAP advice for symptom management in secondary care were recruited at follow-up (defined as >6 months after the patient received low FODMAP diet advice) from 6 UK centres. Questionnaires assessing gastrointestinal (GI) symptoms, effect on socialising as well as dietary intake at long-term follow-up were completed by subjects.

 

660 patients were invited to participate from 6 UK centres, of which 205 participants completed the study. Patients had received dietetic-led FODMAP advice between 2010-2019 with a mean follow-up duration of 44±30 months. 50% had IBS-D, 12% had IBS-M, 15% had IBS-C and 23% had IBS-U.

 

The study found that overall symptom response to the LFD at long-term follow-up was 60% which is comparable to findings of another study of shorter follow-up duration (6-18 months post LFD advice). This current study also demonstrated the efficacy of LFD independent of IBS subtype. The vast majority of patients at long-term follow-up were on the personalisation phase of the LFD (pLFD) with only a small minority still in the restriction phase. Adherence to diet appeared good with those more strictly adhering achieving better symptom improvement.

 

Whilst the intake of energy and the majority of macronutrients failed to meet Dietary Reference Values (DRVs), the nutritional intake of those on a pLFD was similar to those on a habitual diet at long-term follow-up. The total and specific FODMAP group intake was assessed with no difference observed between individuals on a pLFD and habitual diet, with no significant reduction in fructan intake noted in those on a pLFD compared to a habitual diet. It is currently unclear what level of FODMAP restriction is required to achieve symptom improvement or resolution in IBS, although less than 12g has been suggested but not validated in the literature. This current study demonstrated higher FODMAP intakes on a pLFD at long term with further research required to elucidate the optimal FODMAP target intake for management of IBS symptoms.

 

As no difference was observed in total and specific FODMAP group intake, the symptom benefit may be due to other dietary components rather than FODMAPs. It may be that a subset of these patients had gluten-sensitive IBS. The commonest dietary requirement for patients on a pLFD whilst eating out was gluten or wheat free with gluten or wheat-free products being the most commonly consumed in this study. This highlights that patients on a LFD at long-term follow-up are commonly seeking a gluten or wheat-free diet and this may be because this leads to a reduction in total fructan or FODMAP intake and thereby leads to symptom improvement. However, it remains unclear which component of wheat leads to symptom improvement in IBS. Alternatively, a gluten or wheat-free diet may be a simpler diet to follow when eating out or purchasing free-from foods due to clear labelling and greater awareness of this diet.

 

Whilst the LFD has been shown to be effective at long-term follow-up, sociability and food-related quality of life (QoL) was affected with issues including the higher cost of the diet, more difficulty eating out and incorporating into daily life as well as lower food and meal-related satisfaction.

In conclusion, the LFD appears to be effective at long-term follow-up for adequate symptom relief in the majority of IBS individuals with no difference in symptom response by subtype. A large proportion purchase gluten or wheat-free products to help manage their symptoms.

 

Rej A, Shaw CC, Buckle RL et al. Digestive & Liver Disease. 2021. https://doi.org/10.1016/j.dld.2021.05.004