Metabolism in Fed and Fast States

Energy Utilization in Different States

• The body primarily uses glucose for energy during the fed state due to the availability of nutrients from food intake.
• During the fasting state, insulin levels in the blood decrease as the body shifts to energy conservation after the lack of food intake.

Hormonal Regulation and Metabolic Processes

• In the fed state, insulin inhibits gluconeogenesis, the process of generating glucose from non-carbohydrate sources, due to elevated insulin levels.
• In the fasting state, glycogenolysis is stimulated to increase blood glucose levels by breaking down glycogen stored in the liver.

Key Organs and Fuel Sources

• The liver synthesizes ketone bodies which serve as a major fuel source during prolonged starvation.
• During long-term fasting or starvation, fatty acids become the primary fuel source for body tissues, providing energy through beta-oxidation.

Protein Synthesis and Insulin Effects

• Amino acids from dietary protein are utilized for the synthesis of new proteins during the fed state, supporting growth and repair.
• High insulin levels during the fed state primarily stimulate anabolic processes, including glycogen synthesis and lipogenesis (fat storage).

Lipid Metabolism and Adaptation

• In the fed state, the breakdown of fatty acids and triacylglycerols is suppressed, preserving energy storage for future use.
• The brain and other tissues adapt to utilize ketone bodies as alternative fuel during starvation, enabling survival despite glucose scarcity.