Humans don’t use as much brainpower as we like to think. Duke Today, Oct. 31, 2017. For years, scientists assumed that humans devote a larger share of calories to their brains than other animals. Although the human brain makes up only 2 percent of body weight, it consumes more than 25 percent of the body’s energy budget. But a comparison of the relative brain costs of 22 species found that other animals have hungry brains too. Picked up by the Daily Mail, IFLScience, Futurity and United Press International.