Metabolic States of the Body: The Postabsorptive State

The postabsorptive state typically begins about four hours after a meal and lasts until the next meal is consumed.

During this period, the digestive system stops absorbing nutrients, and the body utilizes stored energy reserves to maintain stable blood glucose levels.

Initially, the glycogen stored in the liver is broken down to release glucose into the bloodstream.

Additionally, the triglycerides in adipose tissues are broken down into fatty acids and glycerol. During prolonged fasting, tissue proteins are also broken down, releasing amino acids into the blood.

The liver utilizes the glycerol and the released amino acids from the blood as non-carbohydrate sources to produce glucose through gluconeogenesis.

Since the brain and red blood cells use glucose as their primary energy source, the body employs a glucose-sparing strategy, switching other tissues to fuel sources like fatty acids from adipose tissues.

In response to a dip in blood glucose, the pancreas secretes glucagon, which stimulates glycogenolysis and promotes gluconeogenesis.