INS and type 2 diabetes mellitus: Loss of fat storage-inducing transmembrane protein 2 (FIT2) and lipid droplets (LDs) in β-cells lowers β-cell ATP levels, increases intracellular ceramide C16: 0 accumulation, stimulates ER stress, diminishes calcium signaling, inhibits vesicle exocytosis, downregulates β-cell transcription factors, upregulates unfolded protein response genes, and reduces insulin secretion, exacerbating diet-induced T2DM.