|
This is what wikipedia had to say re ketosis.
Complicated as usual.
I have not checked further but according to the below the brain can burn Ketones in part.
Fats can be used as an alternate fuel.
Protein etc can be converted to make glucose.
So a fast would presumably reduce glucose consumption but to what extent and in what time frame etc is not clear.
"When glycogen stores are not available in the cells (glycogen is primarily created when carbohydrates such as starch and sugar are consumed in the diet), fat (triacylglycerol) is cleaved to give 3 fatty acid chains and 1 glycerol molecule in a process called lipolysis. Most of the body is able to utilize fatty acids as an alternative source of energy in a process where fatty acid chains are cleaved to form acetyl-CoA, which can then be fed into the Krebs Cycle. During this process a high concentration of glucagon is present in the serum and this inactivates glucose kinase causing most cells in the body to use fatty acids as their primary energy source. At the same time, glucose is synthesized in the liver from lactic acid, glucogenic amino acids, and glycerol, in a process called gluconeogenesis. This glucose is used exclusively for energy by cells such as neurons and red blood cells.[citation needed]"
"If the diet is changed from a highly glycemic diet to a diet that does not substantially contribute to blood glucose, the body goes through a set of stages to enter ketosis. During the initial stages of this process the adult brain does not burn ketones, however the newborn brain makes immediate use of this important substrate for lipid synthesis in the brain. After about 48 hours of this process, the adult brain starts burning ketones in order to more directly utilize the energy from the fat stores that are being depended upon, and to reserve the glucose only for its absolute needs, thus avoiding the depletion of the body's protein store in the muscles."
|