The sugar:fat ratio is critical (EDIT: or listening is)

[djkvan]

I'm not sure what the answer is, but as a safe guess, I'd say that a very active brain might require 50% more energy at the point in time that it is very active. Like a muscle, though, it is doubtful that the brain can maintain extreme levels of activity over extended periods of time without rest. I wonder what the brain's equivalent to lactic acid is?

Taking more sugar than necessary at one point in time is not healthy for the brain, as illustrated by the following example from http://www.fi.edu/learn/brain/carbs.html

A sugary snack or soft drink that quickly raises your blood sugar level gives you a boost (and any caffeine adds to the lift), but it's short-lived. When you eat something with a high sugar content your pancreas starts to secrete insulin. Insulin triggers cells throughout your body to pull the excess glucose out of your bloodstream and store it for later use.

Soon, the glucose available to your brain has dropped. Neurons, unable to store glucose, experience an energy crisis. Hours later, you feel spaced-out, weak, confused, and/or nervous. Your ability to focus and think suffers. The name for this glucose deficiency is hypoglycemia , and it can even lead to unconsciousness.

[Oscar]

I have no clue (hmm I felt my brain's energy needs drop there for a bit).
The skeletal muscles account for 50% of the total energy need when in rest, and up to 90% when very active.

[RRM]

Taking more sugar than necessary at one point in time is not healthy for the brain

Sure. Thats why you need to listen to your body's need for energy.
On this diet we eat lots of small meals, according to your energy levels.
Hence never too much energy at once.

[djkvan]

The problem I have had is mistaking one thing for another. For instance, what was thought to be insufficient sugar was in fact often too much sugar. As a consequence, much of my recent time was spent in a hyperglycemic state. Yesterday I truly experienced a sugar-spike, its whole cycle, in a mindful way. Now I have a clear idea of what a sugar spike involves for me. Of course it took some research to understand what it can look/feel like to identify it properly. For me it begins with ice cold feet, irritability, mild headache and inability to concentrate/focus. As it levels off my focus improves, but I begin to feel tired and start yawning as the cycle nears its conclusion. By the end of the spike, the temperature of my feet has been restored to normal, and I experience a sensation of false hunger from an equal sugar "dip", which if ignored (and it must be to end the cycle), leads to a state of level focus, emotion and energy. Treating symptoms such as mental fogginess with more sugar was an error, and led to further diabetic symptoms (e.g. numbness in hands and feet), much confusion and anxiety in the last month or so.

[RRM]

For me its hard to imagine consuming too much sugar in one sitting,
as my body always very clearly lets me know.
When its enough, I simply dont feel like drinking another drop, so i dont.
Only when i feel like drinking, i do.

Maybe the key is in really listening to your body instead of rationalizing your energy intake too much.