Irritable bowel syndrome (IBS) is a disorder of gut-brain interaction featuring recurrent abdominal pain or discomfort in conjunction with altered bowel habit 1. Diet is a mainstay of IBS management, with first-line dietary advice being the NICE diet that recommends regular meal size and frequency; maintaining hydration; restricting fatty, spicy and processed foods; and limiting caffeine and alcohol. Second line dietary advice is for the low FODMAP diet (LFD), the most extensively researched whole diet intervention in IBS. FODMAPs are fermentable oligosaccharides, disaccharides, monosaccharides and polyols, some of which increase small intestinal luminal water and some of which undergo colonic fermentation to produce gas that can contribute to IBS symptoms in those with visceral hypersensitivity 2. The LFD has numerous limitations, including being restrictive for patients, risking excessive or prolonged restriction in some, and can impact the gut microbiome 3. The LFD therefore requires expert advice and management from a dietitian, which can be challenging in some healthcare settings for a prevalent disorder commonly managed in the community 3. In this issue of Alimentary Pharmacology & Therapeutics, Garcia-Cedillo and colleagues 4 present data from a randomised clinical trial of a personalised-LFD. The personalised-LFD differed from the full LFD in two ways: first, it only restricted FODMAPs that appeared to result in symptom exacerbation from prospective recording, and second, only major sources of the relevant FODMAPs were reduced and even then only by approximately 50%. The goal of the personalised-LFD was to achieve the therapeutic benefits of the full LFD while maintaining dietary diversity 4. In this randomised clinical trial, there was no difference in the numbers experiencing adequate relief between the personalised-LFD (54.5%) and NICE diet (41.2%, p = 0.33) 4. Response rates to the personalised-LFD (54.5%) were in keeping with some trials of the full LFD that report responses including 52% 5, 55% 6 and 57% 7. Large reductions in energy intake (circa −750 kcal/d) were identified in both groups that do not reflect evidence from other studies, at least some of which may represent under-reporting due to social desirability bias 8. This is not the first study to investigate modification to the LFD. In a small feeding study, blanket restriction only of oligosaccharides (fructans and galacto-oligosaccharides, termed ‘FODMAP simple’) led to no difference in symptom response compared with the full LFD 9. In the current study 4, two active dietary interventions are shown to be no different, which is different from proving they are the same (which would require an equivalence trial) or no worse than the other (which would require a non-inferiority trial). Since they are both active interventions, and there is no control group, we do not yet know whether personalised-LFD and NICE diet are ‘equally effective’ or ‘equally ineffective’. Placebo effects can be considerable in dietary intervention trials. The benefit, or otherwise, of ‘personalising’ or ‘simplifying’ the LFD now needs to be evaluated in adequately powered trials through comparison with both a blinded control group (to identify whether any benefit is greater than placebo) and with a full LFD (to identify whether any benefit is as good as the LFD). The data presented here by Garcia-Cedillo and colleagues 4 provide evidence to justify such carefully executed dietary intervention trials. Kevin Whelan: writing – original draft, conceptualization. The author has nothing to report. K.W. has received research grants related to diet and gut health and disease from the Almond Board of California, Danone, and International Nut and Dried Fruit Council and has received speaker fees from Yakult. K.W. is the holder of a joint patent (PCT/GB2020/051604) to use volatile organic compounds as biomarkers in irritable bowel syndrome for which there is currently no commercial product on the market. K.W. receives royalties from Wiley Publishing in relation to academic textbooks on Advanced Nutrition and Dietetics. This article is linked to Garcia-Cedillo et al. paper. To view this article, visit https://doi.org/10.1111/apt.70601. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
Kevin Whelan (Wed,) studied this question.