Type 1 is the less common form of diabetes. In Type 1, the body produces little or no insulin, which is needed for proper cell metabolism. Insulin is the "key" which opens up cells for glucose to enter and give the body energy. Untreated diabetes results in significant weight loss and intense thirst since insulin is lacking. For this reason, a Type 1 person needs to take daily injections of insulin, carefully watch diet (carb-count), regularly test blood-glucose, and regularly exercise. In addition, insulin pump therapy is considered the "tightest" form of control -if followed properly.
In Type 2, the body produces insulin however, it doesn't produce enough of it, or doesn't use it effectively. For this reason, oral antidiabetic agents are taken which acts to "tickle" the pancreas into production. In the majority of type 2 cases, obesity is often a cause. Often times when weight is lost in Type 2's, the diabetes symptoms may disappear.