Your brain accounts for less than 2 percent of your body weight, but on average burns 20 percent of your body’s energy, according to the Physics Factbook.
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Think the Burn
If you consume 2000 calories per day, on average, about 400 calories is burned by brain activity.
Your brain cells use more energy than most of the other cells in your body because your brain is always at work. Even while you sleep, much of your brain is busy managing your body’s physiological and biochemical operations.
Thought is Cheap
Most of your brain’s energy use is dedicated to operating your body -- and not to self-conscious thinking per se. Still, use of particular areas of the brain does consume energy, reports Scientific American. Rats doing complicated maze-work had a 30 percent fall in glucose in their hippocampus — the part of their brain responsible for storing and coordinating memories.
The main source of energy for your brain comes from blood glucose, which is sugar in your bloodstream derived from food you eat. After you eat, your body stores excess blood glucose as a fat, glycogen, for later energy use. Your brain has no way to store glucose. When your blood sugar is low, your brain operates less efficiently. You feel unfocused and spacey and your memory works less effectively because your brain is deprived of energy.