New Therapies in Irritable Bowel Syndrome: What Works and When

Orla Craig

Disclosures

Curr Opin Gastroenterol. 2018;34(1):50-56. 

In This Article

Diet

Before considering medical therapy, a discussion in relation to the potential role of dietary manipulation in alleviating symptoms is generally warranted. 50% of patients with IBS relate their symptoms to food ingestion[15] and many will limit or exclude certain foods without professional counselling.[16] Food-related symptoms in IBS frequently represent an exaggerated physiological response. Ingestion of a fatty meal has been shown to induce greater colonic motor activity in patients with IBS compared with healthy controls,[17] whereas infusion of duodenal lipids increases visceral hypersensitivity as measured by colonic barostat.[18] The role of food allergy in IBS is somewhat contentious. Food allergy testing is freely available online and in many health food stores. Although there appears to be an increased incidence of atopy in functional gastrointestinal disorders[19] there is no convincing evidence linking IgE-mediated food allergy to IBS.[15] IgG levels are generally accepted not to be associated with food allergy.[20] Despite this a number of studies have suggested a benefit of IgG-directed food-elimination diets in IBS.[21–23] The studies in question, however, were limited by small numbers and methodological flaws and the evidence to support IgG-guided food elimination diets is best considered inconclusive at present.

Although IBS is no longer viewed as a condition of inadequate fibre intake, a systemic review and meta-analysis suggested that insoluble fibre such as psyllium or ispaghula may be beneficial in the treatment of IBS with a number needed to treat (NNT) of 6.[24] Conversely insoluble fibre such as bran can exacerbate symptoms such as distension and flatulence.[25] Arguably the dietary alteration with the best evidence to support its use in IBS is the low FODMAP diet. FODMAPS (fermentable oligosaccharides, disaccharides monosaccharides and phenols) are short-chain fatty acids that are poorly absorbed in the small intestine and as such are delivered to the colon where they are rapidly fermented by gut bacteria, producing gas. They are also osmotically active, increasing the water load to the colon.[26] Although food high in FODMAPs has this effect in both patients with IBS and healthy volunteers, in patients with IBS, FODMAPs are likely to induce symptoms such as pain, bloating, wind and diarrhoea.[27] Two recent meta-analysis have concluded that when compared with a Western diet, a low FODMAP diet has a favourable impact on IBS symptoms, particularly abdominal pain, bloating and diarrhoea.[28,29] The low FODMAP diet is complex and guidance by a dietician is advised to avoid nutritional deficiencies. It also carries some theoretical concerns in relation to reducing fibre intake and its effect on the microbiota content and activity. Indeed, this theoretical concern in relation to the microbiota was recently confirmed by Staudacher et al.[30] who identified that those on a low-FODMAP diet had a lower abundance of Bifidobacterium spp. in faecal samples compared with those on a sham diet. Interestingly this change was reversed by coadministration of a probiotic. Studies investigating the efficacy of a low-FODMAP diet have in general used a normal diet as a comparator. There is some recent evidence to suggest that although a low-FODMAP diet is efficacious in reducing symptoms in IBS, it is not more effective than the traditional dietary advice given to this patient group such as eating regular small meals, avoiding insoluble fibre, excess caffeine and gas-producing foods.[31*,32]

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