A 25-year-old man with type 1 diabetes on an insulin pump and continuous glucose monitoring on optimal blood glucose control (HbA1c 6.5%, 48 mmol/mol; glucose time-in-range 70-180 mg/dl, TIR, 90%; coefficient of variation, CV, 36%) switched to a fruitarian diet because of ideological beliefs. This evidence concerns the gene INS and type 1 diabetes mellitus.