Dr. Perlmutter’s Grain Brain diet suggests all carbohydrates destroy the brain, including the “good carbohydrates.” It’s worth noting Dr. Perlmutter’s field of specialty is neurology, not nutrition. One may understand prescribing a low carbohydrate diet for those developing neurological conditions, but for healthy individuals, it can do more harm than good. The average brain relies on 120 g of carbohydrates daily for regular function.
He recommends relying on a diet high in cholesterol and fat even though carbohydrates are the preferred fuel source for the brain. Without an adequate amount of carbohydrates, carbohydrate malabsorption, glycogen storage disease, diabetes melltitus and resorting to using fat as a fuel source can occur. If fat is used as a primary energy source, ketone production can occur in the liver and ketones will start to be used as fuel. In a ketogenic stage, an intermediate stage of starvation can arise and can cause ketoacidosis. 1 
Energy from carbohydrates is stored temporarily in cells in the form of ATP. Glucose production is necessary for energy in muscle cells, brain and red blood cells. Carbohydrates are easier to metabolize than fat and protein due to their accessibility to the body and since glucose is the mostimportant energy source. The concentration of glucose within one’s bloodstream dictates the actions of insulin. Fiber only comes from carbohydrates and has the potential to supplement viscous subgroups by reducing ileal bile acid absorption. Some simple and complex carbohydrates have their own enzymatic oxidation pathways (i.e. lactose requires lactase enzyme to break down into monosaccharides).
Carbohydrates are used for structural support and for storage of glycogen and starch. If there is an excess amount of carbohydrates consumed, they are broken down into acetyl CoA, which is used for fatty acid synthesis. Even though hydrophobic lipids are a more compact form of energy storage than hydrophilic carbohydrates, glucose is not able to be synthesized from lipids.
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Sources: http://www.drperlmutter.com/about/grain-brain-by-david-perlmutter/
http://chriskresser.com/do-carbs-kill-your-brain
http://nevergiveup283to140.tumblr.com/CleanEating
1. Mann J. Dietary carbohydrate: relationship to cardiovascular disease and disorders of carbohydrate metabolism. Eur J Clin Nutr. 2007;61(Suppl. 1):S100–11.
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