In humans, the brain accounts for ~2% of the body weight, but it consumes ~20% of glucose-derived energy making it the main consumer of glucose.

Unlike other tissues, the brain lacks “fuel stores” so it requires a continuous supply of glucose.

Dependence of the brain on glucose as its obligatory fuel derives mainly from the blood-brain barrier (BBB) and its selective permeability for glucose in the adult brain. Glucose cannot be replaced as an energy source but it can be supplemented, as during strenuous physical activity when blood lactate levels are elevated or during prolonged starvation when blood levels of ketone bodies are elevated.

Too little or too much glucose can impair brain function, as you may see when people get “hangrY