Protocol for a pilot single-centre, parallel-arm, randomised controlled trial of dietary inulin to improve gut health in solid organ transplantation: the DIGEST study

INTRODUCTION: Kidney transplantation remains the best treatment for end-stage kidney disease, however the requirement for indefinite immunosuppression increases the risk of cardiovascular disease, cancer and infection, leading to a reduction in long-term patient and graft survival. The gut microbiome is a critical determinant of health and modulates host immunity and metabolism through a number of recognised pathways, including through the production of immunomodulatory short-chain fatty acids (SCFA). Dietary supplementation with non-digestible fibre can augment the microbial production of SCFA and lead to favourable immune and metabolic outcomes, although this has yet to be shown in human kidney transplant recipients. METHODS AND ANALYSIS: Dietary inulin for gut health in solid-organ transplantation (DIGEST) is a single-centre, unblinded, pilot parallel-arm randomised controlled trial designed to assess the feasibility and adherence of dietary inulin, a naturally occurring dietary fibre, in the early post-transplant period in kidney transplant recipients. Participants will be randomised at day 28 post-transplant to a 4-week period of dietary inulin (10–20 g/day) in addition to standard care, or standard care alone, and followed-up until week 12 post-transplant. The primary outcomes of the study are: (i) the feasibility of participant recruitment, randomisation and retention; (ii) adherence to the intervention (inulin) and (iii) the tolerability of inulin determined by changes in gastrointestinal symptoms as scored on the Gastrointestinal Symptom Rating Scale. Secondary outcomes include: (1) glycaemic variability determined by continuous glucose monitoring; (2) abundance of SCFA-producing microbiota, as determined by 16s rRNA sequencing of the faecal metagenome; (3) serum SCFA concentrations; (4) peripheral blood immune cell populations; (5) recipient inflammatory and metabolic profiles and (6) the incidence of biopsy-proven acute rejection and kidney function determined by estimated glomerular filtration rate. ETHICS AND DISSEMINATION: All study visits, clinical and laboratory assessments will be integrated into usual post-transplant care, creating no additional healthcare encounters or procedures. The risks associated with this study are minor. Inulin has been shown to be well tolerated across a variety of cohorts, with the occurrence of short-term adverse gastrointestinal symptoms self-limiting. However, with gastrointestinal adverse events common following kidney transplantation, the tolerability of inulin in this cohort remains unknown. The results of DIGEST will be published in peer-reviewed journals and presented at academic conferences. This study has been approved by the Sydney Local Health District’s Ethics Committee (Royal Prince Alfred Hospital Zone). TRIAL REGISTRATION NUMBER: ACTRN12620000623998.