That is a interesting question on what the body is converting to glucose.
I believe that the human body
- while on LC diet has normal blood glucose level
- can generate glucose via glyconeogensis
- stores glucose into fatty acids/fat
- while on LC diet is metabolizing fat/fatty acids
- can survive on a fat only diet
There is known pathways for converting protein into the starting material for glyconeogensis. So that could be the glucose source.
The question is that has not been addressed is fat being converted into sugar. It seems strange to store glucose into fat and not have a mechanism to retrieving the glucose.
There is no known metabolic pathway for converting fat into sugar in most animals. Not known does not mean there is none or that it has been ruled out as never happening.
In protozoa (single celled organisms) and plants, there are glycosomes, a membrane-enclosed organelle that contains the glycolytic enzymes. The glyoxylatic enzymes can convert the products of fat catabolism into the starting materials for glyconeogensis.
There are similar structures in the liver called Peroxisomes. They are present in all animals. Their numbers appear to increase when someone is on a LC diet.
The end point of fat metabolism is acetyl-CoA. This happens inside the mitochondria. There is a funky mechanism in the mitochondria wall for moving malate in/out of the mitochondria, the malate-aspartate shuttle (sometimes also the malate shuttle). It has been given the assignment as a biochemical system for translocating electrons produced. Malate is converted to oxaloacetate which is used as the starting material for glyconeogensis. Although this mechanism does exchange energy, it is interesting that it is cyclic. It goes both into and out of the mitochondria.
What is missing is the enzymes for changing acetyl-CoA into malate or the glyoxylate cycle. There is some (inconclusive) evidence that these structures could have glycolytic activity.
If this was true, it might explain a lot about the relative success of ketotic/LC diets.
P