Metabolic Stress Testing Reveals Persistent Lipid‐Handling Dysfunction in Women With Polycystic Ovary Syndrome Despite Exercise Training

AIM: Polycystic ovary syndrome (PCOS) is associated with insulin resistance and metabolic dysfunction, yet baseline metabolomic studies show inconsistent findings. We investigated whether metabolic abnormalities in PCOS emerge under physiological stress and how these responses are modified by exercise training. MATERIALS AND METHODS: Twelve women with PCOS and 10 controls completed hyperinsulinaemic-euglycaemic clamps with randomised saline or lipid infusion, before and after 8 weeks of supervised exercise. Plasma metabolomics (163 metabolites) were measured at baseline, post-infusion and post-clamp. Linear mixed-effects models assessed Group × Timepoint × Intervention interactions. RESULTS: No baseline metabolite differences were observed between groups. A significant three-way interaction (p = 0.008) indicated condition-dependent trajectory divergence. Post hoc analysis revealed a specific divergence during post-exercise lipid challenge (p = 0.048). Women with PCOS showed reduced suppression of ether-linked phosphatidylcholines during insulin-stimulated lipid loading (PC ae C44:4, p = 0.031), despite exercise-induced improvements in fitness and normalisation of amino acid profiles. Exploratory metabolite ratios suggested impaired substrate coordination under stress. CONCLUSIONS: Metabolic defects in PCOS are stress-dependent and not detectable at rest. Exercise training improves resting metabolism but reveals persistent impairment in adaptive lipid handling during combined insulin and lipid challenges, suggesting impaired coordination of substrate supply during metabolic stress. TRIAL REGISTRATION: ClinicalTrials.gov identifier: ISRCTN42448814.