Why replacement, not repair
Type 1 diabetes is absolute insulin deficiency. No drug can restore beta-cell function reliably, so treatment replaces the missing hormone. The goal is to reproduce the normal pattern of insulin delivery closely enough to keep glucose in range without causing hypoglycemia.
Basal and bolus components
Physiological insulin secretion has two parts. Basal secretion maintains a low steady level between meals and overnight. Bolus secretion rises sharply after eating. Replacement therapy mirrors this with a long-acting basal insulin and rapid-acting mealtime insulin. The basal dose covers glucose produced by the liver in the fasting state; the bolus dose covers the glucose absorbed from a meal. Matching the bolus to carbohydrate intake and pre-meal glucose is the core skill of type 1 management.
What happens without insulin
Without insulin, muscle and adipose tissue take up little glucose, the liver continues to release glucose, and lipolysis releases free fatty acids that the liver converts to ketone bodies. The result is hyperglycemia plus ketoacidosis. This is why insulin omission in type 1 diabetes is dangerous within hours to days, not weeks.