This study will look at the effects, good and/or bad, of treating primary brain cancers with diet therapy using an energy restricted ketogenic diet (ERKD) that uses food. An energy restricted ketogenic diet is a diet designed to keep blood sugars in the low range of normal while at the same time increasing the blood concentration of metabolic break down products called ketones. This diet is currently used to treat children with uncontrollable seizures. This diet is well tolerated by the children with minimal side effects reported after using the diet for years.