What is the primary distinction between type 1 and type 2 diabetes mellitus?

The primary distinction between type 1 and type 2 diabetes mellitus lies in their underlying mechanisms and treatment approaches. Type 1 diabetes is primarily characterized by an autoimmune destruction of the insulin-producing beta cells in the pancreas, leading to an absolute insulin deficiency. As a result, individuals with type 1 diabetes require exogenous insulin for survival and blood glucose management.

In contrast, type 2 diabetes typically involves insulin resistance, where the body's cells do not respond effectively to insulin, and may also feature a relative insulin deficiency as the disease progresses. Many individuals with type 2 diabetes can initially manage their blood glucose levels through lifestyle modifications, such as diet and exercise, as well as the use of oral hypoglycemic agents. This flexibility in management is a key factor in distinguishing the two types of diabetes.

This understanding underscores why the correct answer emphasizes that type 1 diabetes necessitates insulin therapy, whereas type 2 diabetes can often be managed through various means, including diet and oral medications.