Question

what happens in glucose homeostasis when someone fasts for over a week.

Answer 1

In the absence of external Glucose source, the body starts synthesizing glucose via gluconeogenesis using the non-carbohydrates precursors from the body (glycerol from the breakdown of triglycerides, lactate during anaerobic glycolysis and amino acids from muscle protein degradation). 90% of gluconeogenesis occurs in the liver but some occurs in the kidney too.

Insulin regulates gluconeogenesis. When the newly made glucose is sent back to the blood to raise blood glucose, insulin tries to lower the blood glucose level by converting them to glucagon.

In worst case, the ketone bodies are formed when external glucose is unavailable. This provides energy to the brain and heart. Also, prolonged fasting will have a dangerous impact on the body which disturbs the glucose homeostasis and a person can become extremely hypoglycemic and could die due to lack of primary energy source i.e glucose.