In a high protein, very low carb diet, where does the brain get it's needed glucose? The brain does not burn fat, nor protein. It requires sugar. According to Covert Bailey ('Fit or Fat' - book on low fat eating) the body simply converts protein to carbs. If you are not eating enough protein, then the body will break down muscle tissue, otherwise, you are usually spending extra money on protein to create carbs.

12 grams of carbs would equate to about 60 calories. This is hardly enough to run even my pea brain. The sugar's got to come from somewhere.