Do you have a source for this? As far as I am aware your brain mostly burns glucose like the rest of your body. Admittedly glucose is also a sugar, but in the context of this talk sugar refers to sucrose (i.e. the white stuff you put in tea) which is 50% fructose, 50% glucose. Which would imply that sugar is still inefficient "brain fuel" compared to other carbohydrates like pure glucose. If you have any sources/references showing me wrong about the brain metabolizing fructose I'd be very interested and grateful if you could point me to it.