It IS true that carbs can be most easily and quickly rendered into glycogen, which will first feed the brain, be offered to the liver to hold onto, then be offered to the muscles, then turned into fat.
But the amount of carbs the brain needs a day can be equated to the amount you would receive sucking on one piece of hard candy.
This is a very helpful book that clarifies how low carb diets work and takes a very neutral approach: http://www.amazon.com/Diet-101-Truth-About-Diets/dp/0964711656/ref=sr_1_1?ie=UTF8&qid=1352608631&sr=8-1&keywords=Diet+101%3A+The+Truth+About+Low+Carb+Diets