During fasting, how does the body primarily regulate glucose levels?

During fasting, the body's primary method of regulating glucose levels involves utilizing glucagon, which stimulates both glycogenolysis and gluconeogenesis.

When fasting, blood glucose levels tend to decrease because the body is not receiving dietary carbohydrates that would typically increase blood sugar. To maintain adequate glucose levels for critical functions, particularly in the brain, the pancreas secretes glucagon. This hormone signals the liver to convert stored glycogen into glucose (a process known as glycogenolysis), releasing it into the bloodstream. Additionally, when glycogen stores are depleted after prolonged fasting, glucagon promotes gluconeogenesis, the metabolic process that generates glucose from non-carbohydrate sources, such as amino acids and glycerol.

This mechanism ensures that essential glucose is available to tissues that rely on it, such as the brain, maintaining homeostasis even in the absence of food intake. Thus, glucagon plays a vital role during fasting periods to prevent hypoglycemia and sustain energy levels in the body.