Question

During prolonged starvation, the brain increases its use of which of the following substrates in blood as an energy source?

a) Fatty acids
b) Glucose
c) Amino acids
d) Ketone bodies

Answer 1

During prolonged starvation, the brain transitions to using ketone bodies as a primary energy source, which helps to conserve proteins and prevent muscle wasting.

Step-by-step explanation:

During prolonged starvation, the brain significantly increases its use of ketone bodies as an energy source. Initially, the body's primary focus is to provide enough glucose for the brain, but as glucose levels fall, glycolysis is reduced, and the body begins to conserve amino acids by utilizing alternative energy sources, such as ketone bodies. Muscles switch to using fatty acids, while the liver begins to synthesize ketone bodies from the breakdown of these fatty acids. After approximately three weeks of starvation, the brain adapts to utilize ketone bodies as a major energy source, which comprises about 70% of its energy needs. Ultimately, this shift helps to preserve muscle and organ proteins, which would otherwise be catabolized for gluconeogenesis to maintain blood glucose levels.