Authorities like to say that glucose—blood sugar—is your brain’s preferred fuel, but that, again, is because your brain burns glucose for fuel when you’re eating a carb-rich diet. It’s conceivable that our bodies decided, figuratively speaking, that since our brains use up so much of the energy we generate—around 20 percent—having our brains burn glucose would be necessary to control blood sugar in a high-carb world, even if ketones were somehow a better source, like a higher-octane fuel for your car.
