Final answer:
The early phase of starvation involves the depletion of liver glycogen stores and the transition to gluconeogenesis, which leads to the breakdown of fat and muscle mass for energy production. The body enters a postabsorptive state where it conserves protein and switches to alternative fuel sources such as fatty acids and ketones for vital organs.
Step-by-step explanation:
Early Phase of Starvation
The early phase of starvation occurs when the body starts using up stored glycogen in the liver, which can last for approximately 12 to 14 hours after the last meal. Once these glycogen stores are depleted, the liver begins to synthesize glucose from non-carbohydrate sources through gluconeogenesis, targeting amino acids from muscle tissue. This leads to significant loss of fat and muscle mass as the body breaks down these tissues to provide energy. The process of catabolism, where bodily tissues are broken down, supports vital systems like the nervous system and heart muscle. Symptoms during this phase can include impulsivity, irritability, and hyperactivity, progressing to fatigue and apathy as energy levels decrease.
The postabsorptive state is characterized by the switching of fuel sources from glycogen to fatty acids and ketone bodies, which is an adaptive response during prolonged fasting or starvation to preserve protein and provide energy for glucose-dependent organs, particularly the brain. Muscle tissues begin utilizing fatty acids instead of glucose, conserving amino acids vital for protein maintenance.
When the body is starved of fuel, prolonged fasting triggers a decrease in metabolic rate, an adaptive mechanism intended to conserve energy during periods of scarcity. However, if starvation continues and body fat stores are exhausted, muscle wasting can occur, and the body may resort to ketogenic fat metabolism, resulting in increased ketone body production.