Uncontrolled Type 1 diabetes causes the body to burn its own fat and muscle tissue for energy.

Without enough insulin, the body cannot move glucose from the bloodstream into the cells. The cells send out urgent starvation signals. In response, the body begins to break down its own stored fat and muscle tissue to supply alternative energy. This metabolic self-cannibalization leads to rapid, unintentional weight loss. It happens even if the person is eating far more food than usual.