The brain relies on glucose for energy1
The brain is one of the most metabolically active organs in the body. Together with the heart, liver, and kidneys, it consumes about 60% of the body’s energy requirements.1
The heart and kidneys are more metabolically active than the brain, but as the brain is larger, it takes a higher proportion of the body’s energy needs. At rest, it uses approximately 20% to 23% of the body’s total energy requirements, despite accounting for only 2% of the body’s mass. Almost all of that oxygen is used to oxidize glucose to carbon dioxide and water.1
The brain stores little energy as glycogen and relies almost entirely on circulating glucose for fuel. Once inside neurons, glucose is metabolized by mitochondria in a number of steps to produce cellular energy, or adenosine triphosphate.2
Most of the glucose consumed by the brain is used to maintain synaptic function and resting potential of neurons.1 The energy requirements of different types of neurons varies. Large-projection neurons with relatively long axons are most affected by Alzheimer’s disease and these neurons generally have high energy requirements. Without sufficient energy supply, these neurons cannot function efficiently.3
Metabolism of glucose in neuronal mitochondria2
Cytoplasmic glucose undergoes glycolysis to produce acetyl CoA, which is then used to produce ATP. Acetyl CoA, acetyl coenzyme A; ATP, adenosine triphosphate; TCA cycle, tricarboxylic acid cycle (also known as the citric acid cycle or Krebs cycle).