What is the role of gluconeogenesis in fasting?

• A. It does not contribute to glucose production during fasting
• B. Gluconeogenesis is suppressed by insulin during fasting
• C. It produces ketone bodies as the main energy source
• D. Endogenous glucose production by gluconeogenesis provides the body with sufficient glucose for glucose-dependent processes

Answer: (D)

During fasting, the body must keep blood glucose available for tissues that depend on it. Gluconeogenesis, mainly in the liver and kidney, creates new glucose from non-carbohydrate substrates and becomes a key source of endogenous glucose when dietary intake stops. This ongoing glucose production maintains blood glucose at levels that support glucose-requiring processes, such as red blood cells and brain during early fasting; while the brain eventually uses ketone bodies in prolonged fasting, some glucose is still produced to meet the needs of glucose-dependent tissues. Hormonal changes in fasting—low insulin and high glucagon—remove the brake on gluconeogenesis, allowing it to proceed. Ketone production is a separate pathway, not the main product of gluconeogenesis. Therefore, endogenous glucose production by gluconeogenesis provides the body with sufficient glucose for glucose-dependent processes.