Also you don’t need to fast for such as long time to start the burning process. Just cut out sugar and go low carb and do some cardio. They will empty with the change of diet you will be on your way. A little less stressful.
You are burning the stored sugar in your body. Glucose stores. The stuff athletes try to store before they compete. Once you empty the sugar stores and that fuel is gone, you start to move to other sources of fuel.