Resource (1) concludes that there are no convincing studies on the effect of the ketogenic diet in humans. I have not yet reviewed the studies. But according to a quick review of the Abstract, it appears that all the human studies on the ketogenic diet were short term (less than one month).
The following is from Resource (2) p. 25:
.At the most basic level keto-adaptation involves an increase the body’s production and utilization of ketones. However, this is a complex and coordinated sequence of highly orchestrated events requiring adaptation in the type of fuel used by most cells in the body. Ketone production occurs mainly in the liver in response to a combination of increased delivery of fatty acids and and hepatic glycogen reserves. The ketones produced in the liver are then transported by the circulation to other cells in the body including muscle and brain. In skeletal muscle, the first few days of keto-adaptation result in increased use of both ketones plus fatty acids from a variety of sources (adipose or intra-muscular triglycerides, or from circulating very low density lipoprotein particles). Once the process of keto-adaptation is complete (which takes from a few weeks to a month), muscle both at rest and during exercise comes to rely heavily on fatty acids. This adaptation of the muscle away from ketone use spares hepatic ketone production for use by other tissues, especially the brain.
This is a key point. Practically speaking, the brain can burn only glucose or ketones. On a very low carbohydrate diet, the brain comes to rely on ketones as its primary fuel. Although ketones are preferentially taken up by the brain, because of the large mass of skeletal muscle and the increase in blood flow to active muscles during exercise, this delayed shift of the muscles away ketones towards fatty acid use is vital to preserving fuel flow to the brain during exercise in the keto-adapted athlete. In part, the time it takes the body to choreograph these changes in the whole body fuel flow explains why you know adaptation takes a couple of weeks rather than just a few hours or days.
(2) The Art And Science of Low Carbohydrate Performance, 2012 by Jeff S. Volek, PhD, RD and Stephen D. Phinney, MD, PhD
Resources (3),(4), and (5) were found using the Google search term “scholarly articles about ketone used by the brain“. There are a number of other articles on the subject that appear useful. And of course, in the above search, Google suggests alternate search strategies.
(5) Can Ketones Help Rescue Brain Fuel Supply in Later Life? Implications for Cognitive Health during Aging and the Treatment of Alzheimer’s Disease [PubMed Abstract] [Full Text HTML] [Full Text PDF]. Front Mol Neurosci. 2016 Jul 8;9:53. doi: 10.3389/fnmol.2016.00053. eCollection 2016.
We seek to answer the following questions:
How do we correct the dietary errors of the past fifty years?
How do we determine the optimal diet for individuals?
How do we change individual eating and exercise patterns to prevent type 2 diabetes & minimise the effects of insulin resistance?
How can we help everyone eat better to feel better and live better lives?