Purpose
A randomized clinical trial was conducted to evaluate the impact of a gluten-free diet (GFD) on β-cell function and glucose tolerance in persons with multiple islet autoantibodies.

Methods
Individuals (n = 59; median age 11 years) with multiple islet autoantibodies were recruited to a randomized clinical trial between April 2016 and April 2021. The participants were randomized to a GFD (n = 30; female n = 14) or a normal diet (ND) (n = 29; female n = 16). The study was conducted at 6 clinical research centers in Finland and Sweden, with a dietary intervention for 17 months followed by a 6-month washout on a ND. The primary outcomes were (1) the proportion of participants going from normal glucose tolerance at the time of the randomization to abnormal glucose tolerance by 18 months, (2) a change in first-phase insulin response in IV glucose tolerance tests between randomization and 18 months, and (3) a change in C-peptide area under the curve in oral glucose tolerance test between randomization and 18 months.

Results
We did not find differences between participants randomized to GFD and ND in any of the glucose tolerance outcomes. No serious adverse events or adverse events related to a GFD were noted.

Conclusion
Being on a GFD was not found to differ from being on a ND in preserving β-cell function or maintaining normal glucose tolerance in persons with multiple islet autoantibodies.