Exercise Metabolomics Reveals Intensity-Dependent Metabolic Responses Associated with Cardiorespiratory Fitness in Adults with Type 1 Diabetes.

Purpose: To characterize plasma metabolomic responses to maximal exercise and their associations with cardiorespiratory fitness (CRF) in adults with type 1 diabetes. Methods: In this exploratory pooled secondary analysis, 21 adults (67% female; age, 51.6 ± 13.2 years; HbA1c, 67.5 ± 7.0 mmol/mol) completed a cycle-ergometer test to exhaustion; metabolomic data were available for 20. Plasma collected at rest, anaerobic threshold (AT), peak exercise, and recovery underwent targeted and untargeted gas chromatography-mass spectrometry profiling. Peak oxygen uptake (V̇O2peak) quantified CRF. Linear mixed-effects models adjusted for age, sex, HbA1c, and diabetes duration. Results: At the AT, L-(+)-lactic acid and 2-hydroxyisobutyric acid increased relative to rest (both q ≤ 0.010). Peak exercise produced changes in glycolytic, tricarboxylic acid (TCA)-cycle, and purine metabolites, with enrichment of the TCA cycle and nucleotide metabolism. TCA-cycle enrichment persisted during recovery. In exploratory interaction analyses, higher V̇O2peak was associated with increases in L-(+)-lactic acid at AT (β = 0.032, q = 0.040) and peak exercise (β = 0.031, q = 0.024), and in malic acid at peak exercise (β = 0.063, q = 0.010) and recovery (β = 0.061, q = 0.015). Conclusions: These preliminary findings suggest the presence of intensity-dependent and fitness-associated metabolic responses to exercise in adults with type 1 diabetes. Given the small sample size, particularly for interaction analyses, these findings require confirmation in larger independent cohorts.