The goal is to establish the effect of oral inulin supplementation on continuous glucose monitoring (CGM) metrics and immunological parameters in adults with type 1 diabetes. The investigators will perform a double-blind, randomized, placebo-controlled trial in 2x38 participants to measure effects on CGM metrics, gut microbiome composition, residual beta cell and immunological parameters.

The investigators perform a double-blind, randomized, placebo-controlled trial in 2x38 adults with type 1 diabetes. The participants will be given inulin or placebo once daily in powder, which can be dissolved in water and ingested orally, for 90 days. The main study endpoint is the difference in time in range between the groups between baseline and end-of-study. Secondary endpoints include changes in glycaemic variability, time in tight glycaemic range and hypoglycaemic episodes, gut microbiome composition, changes in residual beta cell function, changes in immunological parameters and validated questionnaires (Quality of Life and gastro-intestinal complaints).

Inclusion Criteria:

• A diagnosis of type 1 diabetes, as made by their primary clinician
• A time in range of <80% in the last four weeks before screening

Exclusion Criteria:

• Use of any fibre supplementation (within the last month before screening or ongoing)
• Use of antibiotics in the lasts three months before screening or during study period
• Active infection during the study visit
• Inability or unwillingness to donate feces or urine.
• Illicit drug use (e.g. MDMA/amphetamine/cocaine/heroin/GHB) in the past three months or use during the study period.
• Inability or unwillingness to provide informed consent.
• Absence of a large bowel (ie colostomy)
• Active inflammatory bowel disease

The unblinded researcher will provide the study intervention to the blinded investigator in a coded fashion. Both the investigator and the participant are blinded. In case of emergency, an unblinding protocol is activated.