L.C.H.M. Blok1,2, D.F. de Wit1, S. El Mallali2, J.H.M. Levels1, E.H. Serné1,2, E. Rampanelli1,3, M. Nieuwdorp1,2, N.M.J. Hanssen1,2
1Department of Vascular Medicine, Amsterdam University Medical Centres – Location AMC, Amsterdam, The Netherlands
2Diabeter Center Amsterdam, Amsterdam, The Netherlands
3Amsterdam institute for immunology and infectious diseases, Amsterdam, The Netherlands
Background
Despite advances in insulin therapy and continuous glucose monitoring (CGM), many adults with type 1 diabetes (T1D) do not achieve recommended glycaemic targets. In T1D, higher dietary fibre intake has been associated with improved CGM-derived metrics in observational studies. Fermentable prebiotic fibres such as inulin may further modulate metabolic and immune pathways via microbial short-chain fatty acid (SCFA) production. However, interventional evidence in T1D remains limited. This study evaluated the effect of 12 weeks of inulin supplementation on CGM-derived glycaemic control and immunological parameters in adults with T1D.
Methods
In this double-blind, randomized, placebo-controlled trial, 76 adults with T1D and time in range (TIR) <80% were randomized 1:1 to receive 10 g/day inulin or placebo (maltodextrin) for 12 weeks. The primary outcome was the between-group difference in change in TIR from baseline to end of study, assessed by CGM. Secondary endpoints included glycaemic variability (GCV), glycated haemoglobin (HbA1c), residual beta-cell function (urinary C-peptide-to-creatinine ratio, UCPCR), gut microbiota composition, faecal SCFA concentrations, and a broad panel of inflammatory and immune-regulatory markers measured by ELISA.
Results
Of the 76 participants randomized, 73 (96%) completed the study (inulin n=36; placebo n=37). Baseline characteristics were comparable between groups, with a median age of 40 (28–55) years, diabetes duration of 19 (14–30) years, and mean TIR of 65% (56–71). The intervention was well tolerated. However, no significant between-group differences were observed in change in TIR, glycaemic variability, or HbA1c. Analysis of inflammatory and immune-regulatory markers is ongoing.
Discussion
Twelve weeks of inulin supplementation did not improve CGM-derived glycaemic control in adults with longstanding type 1 diabetes. The absence of an overall effect does not exclude benefits in specific responder subgroups. Ongoing analyses of microbiome and immunological outcomes will clarify biological effects beyond glycaemia and may help identify individuals who benefit most from prebiotic interventions.