Cell health depends on a steady supply of fuel from glucose and free fatty acids. These two major fuels are both regulated by insulin released directly into the blood from beta cells in the pancreas. From the blood, an insulin molecule crosses the blood vessel wall and attaches to an insulin receptor on the outer wall of a muscle, liver or fat cell. This attachment triggers the movement of glucose into the interior of the cell, where it can be converted into energy for metabolism, repair and defense.
In contrast to the complicated transport system for glucose, and to the chagrin of many, fat moves easily across cell membranes. If insulin levels are too low, less glucose enters cells, but more glucose is released by the liver and more fat is released from fat cells. So a low insulin level causes not only a high blood sugar but it also causes more fat to enter the blood.