Best way to lose body fat

What is the best way for a sprinter to lose body fat without losing the explosive conditioning of the muscles? I beleive that the heart rate must be above resting for a minimum of thirty minutes before the body begins to use fat stores for energy. Obviously this is dependent on what you last ate, what you ate, etc. but would it then be beneficial to perform aerobic exercise in the morning, before you eat, whilst the body is starved of nutrients? Logically this seems plausible but I am not entirely sure? On the topic of ‘fat burners’, are there any that work? Have heard many mixed reviews?
Appreciate advice

eat about 3 grapefruits a day. Not only is it the most powerful fat burner its the cheapest. Plus dont forget your cardio!