When the body does not produce enough insulin or use it efficiently, blood sugar levels build in the body. Also, the body's cells do not receive the energy they need from glucose, so the patient may struggle with fatigue. When the body turns to other tissue, like fat or muscle, for energy, weight loss may occur.pecifically, insulin allows the cells in the muscles, fat and liver to absorb glucose that is in the blood. The glucose serves as energy to these cells, or it can be converted into fat when needed. Insulin also affects other metabolic processes, such as the breakdown of fat or protein.