Asked by: Laura Glover, by email
Yes, but the difference is tiny. The common claim that the brain uses 20 per cent of the body’s energy for only 2 per cent of body weight makes it sound very demanding. But this only applies if you keep still. Physical exercise quickly demands lots more calories to power the muscles, while deep thought needs only a few, even if it makes you hungry. In one study some students did intense computer work while others relaxed. There was almost no difference in energy used, but those doing mental work ate 200 more calories afterwards.
This may be because the brain uses glucose for fuel, and intense thought lowers blood glucose levels. Another reason is that the brain never stops controlling breathing, digestion and other bodily functions. At night it is busy dreaming and by day processing information from the senses. All this takes less than one calorie a minute. So even if deep thought doubled the calories used, this would be a small increase compared with getting up and doing something physical.
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