Final answer:
The body uses fatty acids and ketone bodies as alternative energy sources when carbohydrates are insufficient. Ketone bodies are produced through ketogenesis and are used primarily during prolonged energy deficits like starvation or uncontrolled diabetes.
Step-by-step explanation:
When there is an insufficient supply of carbohydrates available for energy, the body will instead use fatty acids and ketone bodies as its primary energy source. Initially, the body uses stored glycogen, but once these stores are depleted, it begins to break down fatty acids. This leads to the production of acetyl CoA and subsequently, if the amount of acetyl CoA exceeds the capacity of the Krebs cycle, the excess is converted into ketone bodies through a process called ketogenesis.
In prolonged periods of starvation or in cases like uncontrolled diabetes, where glucose is not sufficiently utilized, these ketones function as an alternative energy source for the brain and other vital organs. The use of proteins for energy is the body’s last resort, as it leads to the breakdown of functional tissues and eventual muscle wasting.