Editorial: balancing fibre and FODMAPs in IBS – a ‘rye’ look at an old problem

Abstract

Back in the dark ages when we had little to offer the patient with irritable bowel syndrome (IBS) other than a pat on the head (the origin of the problem; as in ‘it's all in your head’) and an anti-spasmodic that made your mouth dry, fibre assumed significant status in the gastroenterologist's therapeutic armamentarium. This was a time when the many benefits of fibre intake to health maintenance and disease prevention had come to be appreciated and it was assumed, given its physiological effects on gut function, that IBS sufferers should benefit. Clinical trials revealed a more complex picture; yes, some did achieve benefit but many did not appreciate the exacerbation of bloating and flatulence that ensued as their fibre intake was increased.1 Within the constraints imposed by the quality of many of the original trials, a recent systematic review has clarified the picture to some extent by indicating that, in IBS, soluble but not insoluble fibre is of benefit and that constipation is the symptom that is most likely to improve with supplementation.2 Now, we enter a new phase in the dietary management of IBS with the appreciation of the negative impact of fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) on symptoms and the demonstration of symptomatic benefits from the institution of a low-FODMAP diet.3 As foods that contain FODMAPs (fruits, vegetables and grains) represent a major source of dietary fibre for many, the institution of a low-FODMAP diet would appear at first flush to fly in the face of conventional wisdom, both in terms of the management of IBS and general health. Allied to the latter are concerns regarding the long-term impact of a low-FODMAP diet, which inevitably removes an important substrate for bacterial metabolism, on the integrity of the gut microbiome4; are we literally robbing Peter to pay Paul? Laatikainen and colleagues have developed an ingenious solution to the fibre/FODMAPs dichotomy.5 Using a specially prepared rye bread that was low in FODMAPs, they still managed to deliver the same amount of dietary fibre as regular bread, yet drastically reduced the amounts of fructans, mannitol and resistant starch. Those who were randomized to the low-FODMAP bread experienced, in comparison to those who consumed regular rye bread, modestly lower scores in several key IBS symptoms, although without any significant impact on the IBS symptom severity score (IBS-SSS) or quality of life. As expected, colonic fermentation, assessed by breath hydrogen excretion, was lower among those randomized to the low-FODMAP bread. This clever study has demonstrated that you can go low-FODMAP and high fibre and still experience improvements in symptoms such as flatulence, cramps, pain and ‘stomach rumbling’; unfortunately, while distension is a component of the IBS-SSS, bloating and distension, so prevalent in IBS, and so frequently exacerbated by fibre, were not reported individually. It is also noteworthy that constipation-predominant IBS subjects were excluded, a group expected to benefit most from fibre. Not surprisingly, therefore, no change in stool symptomatology was evident. Parenthetically, given the debate that surrounds the impact of a gluten-free diet in IBS,6 it should be noted that, although rye is contraindicated for those who have coeliac disease and would be expected to exacerbate symptoms, if a gluten-type response was operative in IBS, those who ingested the low-FODMAP rye bread still derived benefit. This observation supports the contention that it is the removal of fructans (an important FODMAP in rye as well as wheat), and not gluten equivalents, that mediate the benefits of a gluten-free diet in IBS.6 A few words of caution. The study did not meet its primary endpoint and individual symptom benefits were selective and modest. Changes from baseline in individual symptoms are not presented; were they simply less severely exacerbated in the low-FODMAP rye bread group. Furthermore, long-term effects on symptoms and the microbiota are unknown. Are we on the verge of a culinary revolution where the low-FODMAP kitchen and bakery will rival the gluten-free industry? Perhaps not yet, but this innovative study does provide a novel approach to the dietary management of IBS, an approach so dearly sought by its sufferers. Declaration of personal and funding interests: EMMQ has served as an advisory board member for Alimentary Health, Allergan, Biocodex, Rhythm, Salix, Vibrant and served as a speaker for Procter and Gamble, Biocodex and has Research Support from Rhythm, Theravance, Vibrant.