Final answer:
When the body lacks carbohydrates, it produces ketone bodies from the incomplete breakdown of fat. This process, called ketogenesis, generates acetoacetate, β-hydroxybutyrate, and acetone, which are used as alternative fuels.
Step-by-step explanation:
In the absence of carbohydrates, the body resorts to the breakdown of body fat to meet its energy requirements. This process leads to the production of ketone bodies due to incomplete breakdown of fatty acids. Initially, the body uses stored glycogen for energy, but once this is depleted, it turns to stored fat. During fat metabolism, fatty acids are oxidized via β-oxidation into acetyl CoA, which can enter the Krebs cycle to generate ATP. With a shortage of glucose, if excessive acetyl CoA accumulates, the Krebs cycle is overloaded and the acetyl CoA is diverted to create ketone bodies through a process called ketogenesis. These ketone bodies include acetoacetate, β-hydroxybutyrate, and acetone, and can serve as an alternative fuel source, particularly for the brain and muscles when glucose is scarce.
In the absence of carbohydrates, ketone bodies are produced from the incomplete breakdown of body fat. When the body's glycogen stores are depleted, fatty acids become the principal metabolic fuel. The liver then synthesizes ketone bodies from precursors obtained from fatty acid breakdown. Ketone bodies can serve as a source of energy when glucose levels are low.