> The body can burn carbs or fat for fuel.  It generally prefers carbs. Don't give it any carbs, and it has no choice but to burn fat.  Don't give it any fat, and it will burn protein (by turning it into carbs).

The body will burn the macronutrients in this order: carbs, protein, and fat.  But it turn protein into glucose via gluconeogenesis until after daily protein needs are met (about 100 grams or so).  In the situation where you eliminate carbs and limit protein to daily needs, it will burn for fuel whatever fat you consume.  And if that fat intake isn't enough to meet daily energy needs, it will burn stored body fat.  When stored body fat runs out, starvation ensues and the body will start to eat its own muscle.  I'm guessing that not a one of us here have that problem.

Jim