A. I would have been the first to say YES initially. On paper and in theory it looks like the answer is yes. But, after researching the subject, I was surprised to find the answer wasn't what I figured it would be!
The Theory
Doing cardio first thing in the morning when you first wake up will burn body fat for fuel. Food provides energy, particularly carbohydrates. Fasting during the night and doing cardio before consuming any calories, will allow for no carbs in your stomach for fuel. This will cause the body to use it's stored fat for fuel. Makes sense right? The problem with this theory is, the body will still have some stored blood glucose and muscle glycogen which it will use first. The body will then break down protein found in the body for fuel, which will come from muscle and organ tissue. This is known as KETOSIS. Fat, unfortunately is the body's last preferred source for fuel.
In fact, if you perform an intense cardio type workout in a fasted state, your performance will suffer due to lack of fuel and energy, which will affect the rate at which you burn calories during the actual workout session. Therefore, the rate at which you can perform will affect your caloric burn negatively as well.
Bottom Line
I personally have done and continue to do a slow burning cardio workout in the morning when trying to burn body fat. I will typically ride a stationary bike for about 30 minutes at approximately 55-60% my Maximum Target Heart Rate. (220 - age= maximum heart rate (MHR). MHR x .60= 60% maximum heart rate.) I prefer to do this because it sets the tone for the rest of day as far as my mental focus and eating habits. I eat breakfast immediately after the cardio which allows the nutrients to be absorbed more efficiently to replenish glycogen and glucose levels. I then will occasionally do a second half hour of cardio in the evening. I prefer to break my cardio sessions up due to time constraints and mental focus... I get bored easy doing cardio ha ha!
At the end of the day, nutrient dense calories spread throughout the day, strength training to build muscle which raises your resting metabolism and 20-60 minutes of cardio 3-5 times each week are the best methods for losing body fat and toning your body.