The various types of diabetes are different disorders with different causes:
Obesity may be a cause for diabetes
Type 1 Diabetes
This type of diabetes is an autoimmune disease. Your immune system turns on itself and destroys the insulin-producing cells in your pancreas. Although type 1 diabetes usually develops in childhood or teen years, it can appear later.
Type 2 Diabetes
In this type, your pancreas makes some insulin, but not enough. Your cells also can become resistant to insulin's effects, keeping insulin from escorting enough glucose into your body's cells. Type 2 diabetes generally develops after age 40. However, doctors are seeing a rise in childhood type 2 diabetes that parallels the rise in obesity among youth. A form of type 2 diabetes, gestational diabetes, develops during 2 percent to 5 percent of pregnancies. In gestational diabetes, your body doesn't effectively use the insulin you produce. The cause may be metabolic changes that occur due to the effects of hormones in pregnancy. Gestational diabetes usually disappears after pregnancy, but more than half of women who experience it eventually develop a permanent type 2 diabetes.