Ok, firstly you're dealing with the human body. You have several different paths to turn to when it comes to producing energy, but they boil down to three:
- ATP-PC Pathway
- Glycolytic Pathway
- Oxidative Pathway
These energy systems all use and produce ATP (that's the main source of energy) in some way. To get ATP, they either break down:
- These are typically the primary source of energy, yields 4 kcals per gram
- Typically the secondary source, found everywhere but also large stores in the body. It's the most energy dense at 7 kcals per gram
- Typically tertiary, 4kcals per gram
The energy systems work like three dimmer switches. When you're doing something like an endurance sport, i.e. marathon running, you'll switch to oxidative, which will use fat as an energy source. When you're just sprinting or Olympic lifting, you'll use the ATP-PC pathway, which uses carbs. However, you never just turn off one. You'll always use all three-just to differing degrees. Fats, carbs, and proteins can also fuel each pathway.
Now, the critical thing to note here, is that we are not machines. Your body does not burn just fat, or just protein. These energy systems all work at the same time. It's more of a question of what you are doing and for how long that dictates what source of energy your body needs to burn first.
The reason your body will cease to build and repair muscle in a caloric deficit environment is because it needs to save those energy sources over a longer period of time. It's primary job is survival first-and if it's not receiving enough calories, it will hang onto energy stores for later metabolism, vs just repair. Building and repairing muscles costs calories, and the processes for repair are semi-unrelated to metabolism (for the sake of this answer anyway), or your day-to-day activities.
So for your questions, TL,DR:
Now I'm really simplifying this, there's so much more detail about how to answer your question, but it sounds like you want to change your body to run on fat. You can do that, but before you do, take a look at any Olympic athlete-the ultimate expression of prime physical condition. They eat balanced diets, and they train. That's the kind of philosophy you should be looking at, not fad diets.
EDIT: This is a difficult question to answer succinctly.