Glucose is the energy molecule that fuels the body and feeds the brain.
It is derived from the food we eat, primarily carbohydrates.
After carbohydrates are broken down in the stomach, it is absorbed into the blood stream through the small intestine.
In order for glucose to get into the liver and muscle cells to be used for energy, or into the fat cells to be stored for future energy use, it must have insulin.
Insulin is a protein hormone, secreted by the islets of Langerhans in the pancreas, which helps the body use sugar and other carbohydrates.
In normal glucose metabolism, just enough insulin is released to do the job.
The insulin converts the glucose to glycogen and starch, which is stored in the muscles and liver for energy use.
Insulin binds with receptor molecules on the cell membrane.
This creates a "door" that allows the glucose into the cell.
When the cells are full, any leftover glucose is converted to triglyceride and taken to fat cells.
There the insulin binds with receptor molecules on the cell membrane, glucose is taken into the fat cells, and is stored for future use.
When most of the glucose is cleared from the bloodstream, the brain secretes a chemical, serotonin, which signals the body that it is no longer hungry.
It will be 4 or 5 hours before hunger is felt again.
Human glucose metabolism evolved in prehistoric man when his food came unprocessed from the environment.
It was quite adequate for the job.
In our modern society we overload the system with carbohydrates, most of it simple sugars and refined grains.
As we dump that junk into our systems, the pancreas must produce a lot of insulin to take care of it.
All that insulin flooding the system "insults" the cells and causes them to close the receptors to let little or no glucose in, a conditions called insulin resistance.
The glucose remains in the blood stream, causing a release of even more insulin.
Meantime, you are feeling tired and hungry because the muscle cells are not getting any energy and the brain is not releasing serotonin.
The "frustrated" insulin takes it's load of glucose and dumps it into the fat cells where it is converted into fat.
Insulin resistance leads to carbohydrate addiction because the body is begging for energy.
You keep eating the carbs trying to supply that energy.
But it is not getting into the cells and you just keep getting fatter.
If this cycle is not broken, eventually the fat cells also become resistant and you do lose weight, but you don't look good.
You are sick.
Eventually the pancreas wears out and no more insulin is produced.
You are in full blown diabetes.