A low FODMAP diet in patients with Crohn's disease.

Abstract

A low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet is frequently applied to patients with irritable bowel syndrome (IBS) as a treatment to reduce functional gastrointestinal symptoms, with evidence of its efficacy mounting worldwide.1, 2 The success of the dietary therapy is now frequently applied to patients with inflammatory bowel disease (IBD) and co-existing functional symptoms. Evidence for application of a low FODMAP diet in the IBD population is limited to a retrospective study of patients with quiescent IBD and IBS-like symptoms, in which more than 50% of patients had a reduction of symptoms.3 While beneficial for symptom reduction, there is evidence suggesting that a low FODMAP diet also has negative effects on microbiota. This was first suggested in a trial where a dietitian-taught low FODMAP diet reduced relative abundance of fecal Bifidobacteria spp. in IBS subjects compared with parallel cohort of IBS subjects on their habitual diet.4 A more closely controlled trial that compared fecal bacteria of IBS and healthy subjects after being provided two diets that varied only in FODMAP content showed that a low FODMAP diet was associated with reduction of total fecal bacterial load and specific reduction of the highly butyrate-producing Clostridium cluster XIVa and Akkermansia muciniphila, a likely favorable bacteria that promotes short-chain fatty acid production and an increase in the mucus-degrading Ruminococcus torques.5 The application of a low FODMAP diet may raise concerns in the IBS population if applied long term; however, risk to an IBD population may be more significant. Literature suggests that the changes in fecal bacterial seen from a reduced FODMAP intake seem to mimic those seen in patients with Crohn's disease. Patients with Crohn's disease are more likely to have reduced butyrate-producing bacteria, Bifidobacteria spp. and A. muciniphila and increase R. torques and Ruminococcus gnavus.6-8 One bacterium of specific interest in a Crohn's Disease population is the butyrate-producing Faecalibacterium prausnitzii, as mucosal F. prausnitzii has predicted onset of active disease.9 Similarly, in vitro and animal models suggest that A. muciniphila may also predict Crohn's disease activity.8, 10 A low FODMAP diet may further impact negatively on microbiota of patients with Crohn's disease, a population already at risk of dysbiosis. With data indicating that caution should be taken in applying a low FODMAP diet, two different approaches may be used in applying an FODMAP restriction for treatment of functional gut symptoms; the ‘top-down’ or the ‘bottom-up’ approach. The more traditional top-down approach involves the patient restricting all or most foods considered to contain FODMAPs for a four-week to eight-week period. Then, if symptom benefit is seen, dietary liberalization is guided through using set food and dose challenges or general recommendations describing FODMAP dosing across restricted foods. This top-down approach is best suited to patients where the success of a low FODMAP diet or the type or amount of FODMAP tolerance is uncertain; in patients who do not normally eat a lot of FODMAPs or who are very symptomatic; or in patients who would prefer this approach. Conversely, the bottom-up approach involves reducing specific FODMAPs or a few foods that are very high in FODMAPs for a time period then further restriction of foods if necessary. Arguably, this bottom-up approach should be applied in all patients who are at risk of dysbiosis, including patients with IBD. Other indications for this more gentle restriction include patients at risk of nutritional inadequacy or who have other dietary restrictions, which may again encompass the IBD population. Because of the complex and individual nature of an FODMAP restriction, implementation should be done in guidance with a dietitian well versed in IBD, IBS, and dietary FODMAPs. In addition to appropriate FODMAP manipulation, a dietitian will assess and closely monitor nutritional adequacy with dietary restriction and manage as appropriate, including patients in whom nutrient absorption is impaired or dietary intake is altered.