What happens to terminal glucose oxidation during fasting?

• A. It remains unchanged
• B. It increases
• C. It decreases
• D. It fluctuates unpredictably

Answer: (C)

During fasting the body shifts its energy source from carbohydrate to fat. With lower insulin and higher glucagon, fatty acids become the primary fuel for most tissues, and the use of glucose for energy is reduced. The brain eventually adapts by using ketone bodies, which further decreases the need to fully oxidize glucose. As a result, terminal glucose oxidation falls during fasting, even though glucose production processes (like gluconeogenesis) are active to keep blood glucose within a normal range. This metabolic switch explains why the rate of complete glucose oxidation decreases in the fasting state.