Question

What is the main source of blood glucose during the first 16 hrs of fasting and why is that the case?

Answer 1

Glucose is the primary source of energy for cells. The main source of blood glucose during the first 16 hrs of fasting is liver glycogen reserves. When blood glucose levels are reduced, glucagon is released which stimulates glycogenolysis. Epinephrine also promotes glycogenolysis. Glycogen also stimulates gluconeogenesis.

Within 24 hrs, liver glycogen levels are depleted. After that, body depends on fats stored in our body (Adipose tissue). Once fat reserves are also depleted, muscle breakdown occurs (protein utilization)