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How does the endocrine system adjust metabolism during starvation?

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During starvation, the endocrine system shifts the body from an anabolic (fed) state to a catabolic (fasting) state to maintain essential blood glucose levels for the brain and mobilize stored energy.1

This adjustment is primarily driven by a decrease in insulin secretion and a concurrent increase in glucagon secretion from the islets of Langerhans in the pancreas. These hormonal changes trigger several metabolic processes:1

Glycogenolysis: The breakdown of liver glycogen into glucose.1
Gluconeogenesis: The production of glucose from amino acids and glycerol in the liver.1
Lipolysis: The breakdown of triglycerides in adipose tissue into fatty acids, which serve as a primary fuel source.1

As fasting continues, the liver converts fatty acids into ketone bodies. The brain begins utilizing these ketones for energy, which reduces the body's reliance on glucose production and helps spare muscle tissue from excessive breakdown. Additionally, catecholamines may further support these metabolic shifts by stimulating lipolysis and glycogenolysis during periods of stress or low blood sugar.12