During extended fasting, which metabolic pathway is primarily responsible for producing energy from fatty acids?

During extended fasting, which metabolic pathway is primarily responsible for producing energy from fatty acids?

• A. Glycolysis
• B. Ketogenesis
• C. Glycogenolysis
• D. Lipogenesis

Answer: (B)

During extended fasting the body shifts to using fat-derived energy as glucose becomes scarce. Lipids are mobilized and fatty acids are oxidized in many tissues to generate energy. In the liver, however, acetyl-CoA produced from fatty acids is increasingly directed into ketogenesis rather than into the citric acid cycle, because gluconeogenesis consumes oxaloacetate and slows the TCA cycle. This bottleneck funnels acetyl-CoA into producing ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone). These ketone bodies are then released into the bloodstream and used by extrahepatic tissues, especially the brain, as a major energy source during prolonged fasting. So, the pathway that most directly provides energy from fatty acids in this state is ketogenesis, forming ketone bodies that serve as efficient fuel for tissues when glucose is scarce.

During extended fasting the body shifts to using fat-derived energy as glucose becomes scarce. Lipids are mobilized and fatty acids are oxidized in many tissues to generate energy. In the liver, however, acetyl-CoA produced from fatty acids is increasingly directed into ketogenesis rather than into the citric acid cycle, because gluconeogenesis consumes oxaloacetate and slows the TCA cycle. This bottleneck funnels acetyl-CoA into producing ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone). These ketone bodies are then released into the bloodstream and used by extrahepatic tissues, especially the brain, as a major energy source during prolonged fasting. So, the pathway that most directly provides energy from fatty acids in this state is ketogenesis, forming ketone bodies that serve as efficient fuel for tissues when glucose is scarce.