The relevant literature was retrieved by searching for the terms insulin resistance, autoimmunity, hepatic/muscle/adipose tissue/whole-body insulin resistance, glucagon, islet amyloid polypeptide (IAPP), mitochondria/oxidative stress, metabolic memory/legacy effect, sleep, insulin treatment, metformin, SGLT-2 inhibitors, GLP-1 receptor agonists, exercise, physical activity/inactivity, glucotoxicity, lipotoxicity, MASLD/metabolic dysfunction–associated steatohepatitis, and obesity, all related to T1D from 1980 to June 2024 in PubMed. This evidence concerns the gene IAPP and obesity due to melanocortin 4 receptor deficiency.