Ketosis is a metabolic state that may occur during fasting, starvation, or chronic feeding or ketogenic diet. Since the 1920s, ketogenic diet conditioning has been known to be effective with the treatment of childrens with epilepsy. Over the decades, more and more neuroprotective functions of ketogenic diets were reported. However, the biochemical mechanisms underlying the 'magic' of ketosis is still being explored by scientists. The author of this book sought to understand the energy metabolism underlying the ketosis process. He and his colleagues applied metabolic imaging techniques and biochemical assays to elucidate glucose and ketone body metabolic fates in the brain. They advocate that during ketosis, ketone body replaces glucose in many steps of brain biochemical reactions. They believed that ketone body sparing of glucose metabolism, particularly in the fate of brain amino acids, are the key to understanding the 'magics' of neuroprotection.