Fermentable carbohydrates and functional gastrointestinal symptoms in patients with inactive inflammatory bowel disease

Student thesis: Doctoral ThesisDoctor of Philosophy


Many patients with inactive inflammatory bowel disease (IBD) continue to experience functional gastrointestinal symptoms (FGS) despite minimal objective evidence of GI inflammation, with a significant impact upon health-related quality of life. The low FODMAP diet is effective for the management of irritable bowel syndrome (IBS) and retrospective and prospective uncontrolled studies indicate that it may reduce FGS in patients with inactive IBD. However, this is yet to be confirmed in a randomised placebo-controlled trial. The low FODMAP diet reduces abundance of immune-modulatory Bifidobacteria and Faecalibacterium prausnitzii in IBS, alterations that may have clinical implications were they to occur in IBD.
The aim of this thesis was to establish the role of FODMAPs in FGS in IBD. Firstly, a case-control study was conducted to establish FODMAP intakes in patients with active IBD, inactive IBD with FGS and inactive IBD without FGS compared to healthy controls. This showed that patients with inactive IBD with FGS had lower GOS and polyol intakes than healthy controls, although whether FODMAPs induce symptoms in patients with inactive IBD remained unclear.
Therefore, a randomised, placebo-controlled re-challenge trial was designed to establish the effects of pure FODMAP challenges on GI symptoms. A pure fructan challenge induced FGS in patients with inactive IBD, proving FODMAPs as possible inducers of FGS in IBD. However, this trial did not establish efficacy of the low FODMAP diet compared to a placebo diet.
Therefore, a randomised controlled trial was conducted to investigate the effect of the low FODMAP diet on FGS in patients with inactive IBD. Patients with Crohn’s disease and ulcerative colitis with minimal GI inflammation were randomised to either low FODMAP or placebo sham dietary advice, which was followed for 4 weeks. At end of trial, significantly more patients reported adequate relief of GI symptoms in the low FODMAP diet group (14/27, 52%) than the sham diet group (4/25, 16%; P=0.007). There was a greater reduction in IBS Severity Scoring System score in the low FODMAP diet group (-67 SD 78) compared to the sham diet group (-34 SD 50) although this failed to reach significance (P=0.075). There was significantly lower Bifidobacterium longum (P=0.006), Bifidobacterium adolescentis (P=0.005) and Faecalibacterium prausnitzii (0.038) following the low FODMAP diet compared to sham diet. Reassuringly, inflammatory markers and gut-homing T-cells were not different between the diet groups.
This thesis has established that patients with IBD restrict dietary fermentable carbohydrates, and that certain types induce FGS in patients with inactive IBD. Additionally, a low FODMAP diet improves FGS in these patients but reduces immune-regulatory GI bacteria abundance, a finding that requires further investigation.
Date of Award2018
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorKevin Whelan (Supervisor)

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