This review explores our current understanding of the complex interaction between environmental risk factors, genetic traits and the development of inflammatory bowel disease. The primacy of environmental risk factors is illustrated by the rapid increase in the incidence of the disease worldwide. We discuss how the gut microbiota is the proximate environmental risk factor for subsequent development of inflammatory bowel disease. The evolving fields of virome and mycobiome studies will further our understanding of the full potential of the gut microbiota in disease pathogenesis. Manipulating the gut microbiota is a promising therapeutic avenue.

BackgroundOverweight and metabolic problems now add to the burden of illness in patients with Inflammatory Bowel Disease. We aimed to determine if a program of aerobic and resistance exercise could safely achieve body composition changes in patients with Inflammatory Bowel Disease.MethodsA randomized, cross-over trial of eight weeks combined aerobic and resistance training on body composition assessed by Dual Energy X-ray Absorptiometry was performed. Patients in clinical remission and physically inactive with a mean age of 25 ± 6.5 years and Body Mass Index of 28.9 ± 3.8 were recruited from a dedicated Inflammatory Bowel Disease clinic. Serum cytokines were quantified, and microbiota assessed using metagenomic sequencing.ResultsImproved physical fitness was demonstrated in the exercise group by increases in median estimated VO2max (Baseline: 43.41mls/kg/min; post-intervention: 46.01mls/kg/min; p = 0.03). Improvement in body composition was achieved by the intervention group (n = 13) with a median decrease of 2.1% body fat compared with a non-exercising group (n = 7) (0.1% increase; p = 0.022). Lean tissue mass increased by a median of 1.59 kg and fat mass decreased by a median of 1.52 kg in the exercising group. No patients experienced a deterioration in disease activity scores during the exercise intervention. No clinically significant alterations in the α- and β-diversity of gut microbiota and associated metabolic pathways were evident.ConclusionsModerate-intensity combined aerobic and resistance training is safe in physically unfit patients with quiescent Inflammatory Bowel Disease and can quickly achieve favourable body compositional changes without adverse effects.Trial registrationThe study was registered at ClinicalTrials.gov; Trial number: NCT02463916.Electronic supplementary materialThe online version of this article (10.1186/s12876-019-0952-x) contains supplementary material, which is available to authorized users.