Metabolomic Signatures of Transitional Breast Milk in Gestational Diabetes Mellitus: A Case–Control Study Assessing the Impact of Insulin Therapy

<b>Background/Objectives</b>: Gestational diabetes mellitus (GDM) alters maternal metabolism during pregnancy and may impact the biochemical composition of breast milk. Given the critical role of human milk in early-life metabolic programming, identifying metabolic alterations in GDM milk and understanding the effects of insulin therapy has important implications for neonatal health. This study aims to investigate the metabolomic profile of transitional breast milk in mothers with gestational diabetes mellitus compared with healthy controls and to evaluate the impact of insulin therapy on milk metabolite composition. <b>Methods</b>: Breast milk samples were collected between postpartum days 10 and 15 from 80 mothers with GDM and 80 matched controls. Metabolomic profiling was performed using gas chromatography-mass spectrometry (GC-MS), and data were analyzed using multivariate and univariate statistical techniques including PCA, PLS-DA, logistic regression, and ROC analysis. <b>Conclusions</b>: A total of 133 metabolites were identified, and GDM mothers exhibited a distinct metabolomic signature characterized by significant alterations in carbohydrate, amino acid, and microbial-derived metabolites. In particular, galactinol, arabitol, and pyrogallol were significantly decreased, while α-ketoglutaric acid and citric acid were elevated in the GDM group. Insulin-treated mothers showed unique metabolic changes involving glycolytic intermediates (glycerone phosphoric acid), purine metabolism (xanthine), and oxidative pathways (isocitric acid, gluconic acid lactone). Multivariate models based on the top metabolites achieved moderate discriminatory performance (AUC = 0.68). GDM is associated with substantial metabolic changes in transitional breast milk, and insulin therapy appears to modulate these alterations further. These findings suggest that maternal metabolic status and its treatment can shape the neonatal nutritional environment, potentially influencing early metabolic programming.