This is an outdated concept. We require far less and the liver will convert protein into glucose to adequately ‘run’ the brain. That’s how we survive in starvation.
The brain will run very nicely on ketone bodies as the other fuel in hybrid engine bodies. There is a transition phase but brain function has been shown to improve on a Low Carb and High Fat diet.
The only cell in the body that requires glucose exclusively is the red blood cell or erythrocyte. It will get that from the gluconeogenesis of glucose from protein when there is no carbohydrate in the diet.