How Much Oxygen and Calories Does the Brain Need?

An adult human brain uses up about 20 percent of the body's oxygen and about 20 percent of the body's energy, meaning that it uses about 400 calories a day in someone who is on a 2,000-calorie diet. Most of this energy is used in firing neurons, but about one-third of it appears to be dedicated to maintaining cell health.

More facts about the brain:

  • Although oxygen is necessary for life, too much oxygen can actually cause brain damage. Researchers have found that using oxygen to treat people who are in cardiac arrest or who have had a stroke might actually be dangerous, because reintroducing oxygen into the body can create free radicals, possibly damaging the brain.

  • The brain dedicates its energy to different processes depending on what the body is doing. For instance, when a person is asleep, the brain tends to do more maintenance work than when the body is awake.

  • Brain cells can begin to die as soon as five minutes after oxygen deprivation begins.

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