The brain, despite its meager weigh-in at two percent of the body's mass, is our most voracious organ. Our brains consume 60 percent of the sugar coursing through our bloodstreams, a total of about 450 calories each day, a couple candy bars worth of energy. And because the brain can't store energy as fat or glycogen—a storage molecule made of glucose—like other parts of the body can, it needs a continuous supply of fuel.