The brain can utilize ketones instead of glucose. Coconut oil is a great source of medium-chain fatty acis (MCFAs) which supply ketones for brain energy.
I know some people talk about how glucose (dextrose) is absorbed in the upper GI and so can't feed candida which mainly colonizes the colon. In my case, I'm pretty sure I had SIFO, in which case it would feed candida. I got over my candida using a very very low carb diet and it was hell. When I ate carbs my candida flared up. Of course my getting cured of candida involved a whole lot more than a no carb diet (read all my posts). I am not saying that my way is the only way to getting cured but if you are asking me if it is OK to eat carbs I will have to say: I Don't Know.