How does fuel oxidation change during fasting?

How does fuel oxidation change during fasting?

• A. It shifts from carbohydrates to lipids as the main oxidative source
• B. It shifts to carbohydrates as the main source
• C. It relies primarily on amino acids for oxidation
• D. It remains unchanged

Answer: (A)

During fasting the body shifts fuel use from carbohydrates toward fats to conserve glucose for essential tissues. Insulin falls and glycogen stores are depleted, so adipose tissue releases fatty acids that become the primary energy source for most tissues. Amino acids are steered toward gluconeogenesis to maintain blood glucose, rather than serving as the main fuel. As fasting continues, the liver also produces ketone bodies from fatty acids, which tissues including the brain can use, further reducing the need for glucose. So, lipid oxidation becomes the main oxidative source during fasting.

During fasting the body shifts fuel use from carbohydrates toward fats to conserve glucose for essential tissues. Insulin falls and glycogen stores are depleted, so adipose tissue releases fatty acids that become the primary energy source for most tissues. Amino acids are steered toward gluconeogenesis to maintain blood glucose, rather than serving as the main fuel. As fasting continues, the liver also produces ketone bodies from fatty acids, which tissues including the brain can use, further reducing the need for glucose. So, lipid oxidation becomes the main oxidative source during fasting.