Metabolism
The brain consumes up to twenty percent of the energy used by the human body, more than any other organ.
[28] Brain metabolism normally is completely dependent upon blood glucose as an energy source, since fatty acids do not cross the blood-brain barrier.
[29] During times of low glucose (such as fasting), the brain will primarily use ketone bodies for fuel with a smaller requirement for glucose. The brain can also utilize lactate during exercise.
[30] The brain does not store any glucose in the form of glycogen, in contrast, for example, to skeletal muscle.
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