BackgroundGlycogen storage disease type Ia (GSDIa) is an inborn metabolic disorder caused by the deficiency of glucose-6-phospatase-α (G6Pase-α) leading to mitochondrial dysfunction. It remains unclear whether mitochondrial dysfunction is present in patients’ peripheral blood mononuclear cells (PBMC) and whether dietary treatment can play a role. The aim of this study was to investigate mitochondrial function in PBMC of GSDIa patients.MethodsTen GSDIa patients and 10 age-, sex- and fasting-time matched controls were enrolled. Expression of genes involved in mitochondrial function and activity of key fatty acid oxidation (FAO) and Krebs cycle proteins were assessed in PBMC. Targeted metabolomics and assessment of metabolic control markers were also performed.ResultsAdult GSDIa patients showed increasedCPT1A,SDHB,TFAM,mTORexpression (p< 0.05) and increased VLCAD, CPT2 and citrate synthase activity in PBMC (p< 0.05). VLCAD activity directly correlated with WC (p< 0.01), BMI (p< 0.05), serum malonycarnitine levels (p< 0.05). CPT2 activity directly correlated with BMI (p< 0.05).ConclusionMitochondrial reprogramming is detectable in PBMC of GSDIa patients. This feature may develop as an adaptation to the liver enzyme defect and may be triggered by dietary (over)treatment in the frame of G6Pase-α deficiency. PBMC can represent an adequate mean to assess (diet-induced) metabolic disturbances in GSDIa.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12263-023-00729-y.