One of the main functions of insulin is to make the cell open its door to glucose. Insulin is likened to a key to open a door. Simply put, insulin resistance is a condition where the door lock is out of order. Although the key is inserted, we cannot open the door, so glucose cannot enter cells. Since glucose cannot enter cells, it accumulates in the circulation causing high blood glucose. In order to keep glucose level within normal limits, the pancreas has to produce more insulin leading to high insulin levels (hyperinsulinemia). Another function of insulin is to prevent fat burning and store excess energy in the form of fat. That is why insulin resistant people don't burn their fat, but store it in their belly fat.