This article cites a number of studies which show the ways that fat gets converted to glucose on a Low Carb diet (We Really Can Make Glucose From Fatty Acids After All! O Textbook, How Thy Biochemistry Hast Deceived Me!).
The common objection to this is that insulin levels are low when eating fat.
Thus, when insulin levels fall and ketone levels rise, as occurs when our carbohydrate intake is low, our cells increase their supply of CYP2E1 and thereby activate the conversion of fatty acids to glucose.
And more details:
methylglyoxal inhibits the breakdown of glucose … when this pathway is activated, we not only convert fatty acids to glucose, but methylglyoxal concentrations rise and inhibit the breakdown of glucose.
Thus, when glucose runs low and we begin subsisting primarily on fatty acids for fuel, we have a coordinated effort to both spare glucose and to make more of it.
Here’s a study of the subject (
Christoph Kaleta, Luís F. de Figueiredo, Sarah Werner, Reinhard Guthke, Michael Ristow, and Stefan Schuster. In Silico Evidence for Gluconeogenesis from Fatty Acids in Humans. PLoS Comput Biol. 2011 Jul; 7(7): e1002116.). If we could not make glucose from fatty acids then we would not be able to survive long fasts because there are parts of our bodies which absolutely require glucose.
Analyzing evidence concerning the detected pathways lends support to their importance during times of starvation, fasting, carbohydrate reduced and ketogenic diets and other situations in which the nutrition is low on carbohydrates. Moreover, the energetic investment required for this pathway can help to explain the particular efficiency of carbohydrate reduced and ketogenic diets such as the Atkins diet.
Although the brain can use ketone bodies in these situations, it still needs a certain amount of glucose, which has critical implications upon starvation and similar conditions.
Another Line of Evidence
An interesting writeup (Glucose from fatty acids: RQ of 0.454) on the generation of glucose from fatty acids(originally from Heinbecker. Studies on the Metabolism of Eskimos., 1928). The Eskimo woman has a very low RQ value on day 3.5 of her fast.
An RQ below 0.69 suggests the generation of oxygen rich molecules from fatty acids. An RQ of 0.454 suggests a huge amount of (probable) gluconeogenesis from fat is going on.