HADH and type 2 diabetes mellitus: First, the network model in Fig. 3d showed a downregulation of metabolic pathways, including the glycolytic pathway (HK1, GPI, PGM1, ENO3, and PKM), TCA cycle (ACO2, IDH3A, OGDH, DLST, SUCLA2, SDHA, FH, and MDH1), and fatty acid β-oxidation (ACADM, DECR1, ECH1, HADH, and HADHB) in T2DM compared with the nondiabetic controls.