Figure 1.

Brain energy metabolism and ketone bodies. (A) Ketone bodies cross the BBB and enter the brain. There are several types of ketone bodies, including BHB, acetoacetate, and acetone. These ketone bodies could cross the BBB and subsequently enter the brain. (B) Ketone body metabolism in a neuron. After food ingestion, glucose changes into pyruvate, which, in turn, is metabolized to acetyl-coenzyme A, which circulates in the citric acid cycle. During fasting, fatty acids change into ketone bodies through β-oxidation. α-Ketoglutarate could change into glutamate, converting to glutamine and GABA neurotransmitters.⁷⁸Abbreviations: BBB, blood-brain barrier; BHB, β-hydroxybutyrate; MCT, monocarboxylate transporter.