During fasting, which process increases to provide fatty acids?

During fasting, which process increases to provide fatty acids?

• A. Protein catabolism
• B. Lipogenesis
• C. Glycolysis
• D. Lipolysis

Answer: (D)

During fasting the body shifts to using stored fats for energy because circulating glucose is low. This shift is driven by lower insulin and higher counterregulatory hormones, which activate hormone-sensitive lipase in adipose tissue. Lipolysis breaks down triglycerides into glycerol and free fatty acids; the fatty acids are released into the bloodstream and taken up by liver and muscle to be oxidized for energy. In the liver, fatty acids can also support ketone body production during longer fasts. Lipogenesis would not increase in this state since it requires insulin; glycolysis is the breakdown of glucose and is less active when glucose is scarce. Protein breakdown can occur later to supply gluconeogenic substrates, but it doesn’t directly provide fatty acids.

During fasting the body shifts to using stored fats for energy because circulating glucose is low. This shift is driven by lower insulin and higher counterregulatory hormones, which activate hormone-sensitive lipase in adipose tissue. Lipolysis breaks down triglycerides into glycerol and free fatty acids; the fatty acids are released into the bloodstream and taken up by liver and muscle to be oxidized for energy. In the liver, fatty acids can also support ketone body production during longer fasts. Lipogenesis would not increase in this state since it requires insulin; glycolysis is the breakdown of glucose and is less active when glucose is scarce. Protein breakdown can occur later to supply gluconeogenic substrates, but it doesn’t directly provide fatty acids.