Insulin Resistance

Key Takeaway:

  • Insulin resistance  (IR) is caused by high blood glucose levels causing insulin receptors to become desensitized to insulin signaling.
  • IR is a hallmark of type 2 diabetes.
  • IR can lead to high blood glucose levels and insulin-dependent cell starvation.
  • If left unchecked, insulin resistance can exhaust the pancreas and reduce or stop insulin production (from exhaustion) altogether.

What is Insulin?

Insulin is a peptide hormone secreted by the pancreas in response to high blood sugar levels. Insulin binds to receptors and signals for glucose to be transported into cells that use insulin-dependent transporters (GLUT4). Skeletal muscle, adipose tissue (fat), and parts of the heart all use GLUT4 transports and are thus insulin-dependent. GLUT1, 2, and 3 are all insulin-independent, meaning they do not require insulin to transport glucose. 

What is Insulin Resistance?

Insulin resistance (IR) describes reduced response to insulin by cells. Over time, insulin receptors can become desensitized by the signals from insulin. This causes them to respond slowly or not at all. (1)

Why Is Insulin Resistance Bad?

When IR occurs, glucose can not be taken into cells as sufficiently, leaving more glucose floating in the bloodstream, and thus higher blood glucose levels. High blood glucose levels are bad on their own, but to make the matter worse, the pancreas will over secrete insulin to try and compensate for the high glucose levels. This can wear out beta-cells and cause a decrease in insulin release, very similar to what type 1 diabetes experience.

Cells in the skeletal muscle and heart both use GLUT4 receptors to transport glucose into these cells. This receptor is insulin-dependent, meaning it requires insulin for glucose transport. When IR occurs, these cells can basically starve because they need glucose for energy, but are unable to get to it because it is trapped in the bloodstream. (2)