Diabetes is a disorder in which the body cannot handle blood glucose, and in the 1920s it was often fatal. Banting and his assistant Best devised a way to suppress pancreatic digestive enzymes and obtained an extract with strong blood-sugar-lowering activity. The substance was later called insulin. In diabetic dogs the injection dramatically reduced glucose, and hospital trials in Toronto rescued a boy who was in a coma. The work confirmed that hormones can control distant organs and helped establish modern endocrinology. Insulin therapy prevents serious complications and has greatly extended patients’ lifespans. The enormous social impact of this breakthrough was recognized with the Nobel Prize.

Before insulin, diabetes therapy relied on extreme starvation diets with poor outcomes. Banting produced a pancreatic atrophy model by duct ligation to eliminate digestive enzymes and used ethanol-acid extraction to obtain active fractions. Macleod supplied metabolic facilities, and chemist Collip improved purity via alcohol precipitation, opening the door to clinical use. In January 1922 insulin reversed ketoacidosis in 14-year-old Leonard Thompson, the first human success. Insulin is a 51-amino-acid peptide activated from proinsulin in β-cells. Binding to its receptor triggers the PI3K/Akt pathway, causing GLUT4 translocation and rapid glucose uptake. Recombinant DNA technology in the 1980s enabled large-scale production of human insulin with high safety. Today, ultra-rapid and long-acting analogs allow individualized glycemic control. The discovery not only transformed clinical medicine but also laid foundations for protein chemistry, molecular endocrinology, and modern biotechnology.

In 1921 Banting and Best showed that extracts from duct-ligated canine pancreas lowered glycemia within minutes after intravenous administration. Macleod ensured rigorous metabolic conditions and statistical analysis, while Collip used fractional alcohol and isoelectric precipitation to remove endotoxins and concentrate bioactivity. Restoration of respiratory quotient, disappearance of ketonuria, and normalization of hepatic glycogen were demonstrated; early human trials reduced fasting glucose by ~40 % and rapidly reversed ketoacidosis. Subsequent crystallization by Abel (1936) and primary-sequence elucidation by Sanger (1955) revolutionized protein chemistry and paved the way for receptor studies. The insulin receptor was identified as a heterotetrameric tyrosine kinase that signals through IRS-dependent PI3K/Akt and MAPK cascades to coordinate metabolism and growth. Recombinant human insulin expressed in E. coli (1978) displaced pancreatic extraction and enabled PK/PD-tailored analog engineering. The 1923 award thus marks a nexus of physiology, pharmacology, and industrial biotechnology, continuing to influence autoimmune diabetes research, islet transplantation, and closed-loop insulin-pump algorithms.