What is the effect of ketogenesis rate during starvation when insulin is low?

• A. Ketogenesis is inhibited
• B. Ketogenesis is promoted
• C. Ketogenesis is unaffected
• D. Ketogenesis stops

Answer: (B)

During starvation, insulin levels fall, and that shift unleashes fat breakdown and ketone production. Low insulin removes the brake on hormone-sensitive lipase in adipose tissue, so triglycerides break down and free fatty acids flood the bloodstream. The liver takes up these fatty acids and converts them into acetyl-CoA through beta-oxidation. Because gluconeogenesis uses oxaloacetate, the TCA cycle has less oxaloacetate available to fully oxidize acetyl-CoA, so more of it is diverted into ketone body synthesis. At the same time, low insulin reduces malonyl-CoA, lifting inhibition on CPT1 and increasing fatty acid entry into mitochondria for oxidation, further boosting ketogenesis. The liver then releases ketone bodies (such as beta-hydroxybutyrate and acetoacetate) to supply energy to the brain and other tissues when glucose is scarce. So, the rate of ketogenesis is promoted during starvation when insulin is low.