The vast majority of all eight key enzymatic complexes of the TCA cycle, namely, citrate synthase (CS), aconitase 2 (ACO2), isocitrate dehydrogenase (IDH), α-ketoglutarate dehydrogenase (αKGDH), succinyl-CoA synthase (SCS), succinate dehydrogenase (SDH), fumarate hydratase (FH), and malate dehydrogenase (MDH), were reduced in VAT and/or skeletal muscle of T2D, hence confirming the significant downregulation of the entire pathway. Here, PHGDH is linked to type 2 diabetes mellitus.