Final answer:
During extended periods of fasting (starvation), the main source of energy is fatty acids oxidation.
Step-by-step explanation:
During extended periods of fasting (starvation), the main source of energy is from fatty acid oxidation.
After several days of starvation, ketone bodies become the major source of fuel for the heart and other organs.
As starvation continues, fatty acids and triglyceride stores are used to create ketones for the body.
Once these stores are fully depleted, proteins from muscles are released and broken down for glucose synthesis.
Overall survival is dependent on the amount of fat and protein stored in the body.