Insulin is a blood glucose-lowering hormone secreted by the beta cells of the pancreas, and it is the only blood glucose-lowering hormone in the body. Other hormones, such as glucagon, glucocorticoids, catecholamines, including epinephrine and norepinephrine, are all antagonistic hormones of insulin and are capable of raising blood sugar. Insulin can promote the synthesis of protein and fat and inhibit the breakdown of protein and fat, and it can inhibit the conversion of glycogen into glucose and promote the synthesis of glycogen, so insulin is a pro-synthetic hormone that can promote the synthesis of protein, fat and glycogen, inhibit the breakdown of protein, fat and glycogen, and reduce the products of sugar isomerization, thus achieving the purpose of lowering blood sugar. When the body does not secrete enough insulin due to various reasons or when resistance to its action occurs, it will lead to a weakening of the hypoglycemic effect and the occurrence of abnormal glucose metabolism or even diabetes.