To answer this question I need to break down the meaning of fasted cardio. Since most people think it just means to do cardio on an empty stomach and yes the stomach indeed is empty when the workout takes place, but the important part is that the body is in a Fasted State which means that the insulin levels are at a low, baseline level and the body is no longer processing food. It is important to note that a type of exercise whether the body is in its fasted state or not won't speed up the fat loss process if you don't know how to have a proper diet.
It has been shown in researches that when you exercise in a fasted state, the lipolysis process increases as well as the fat oxidation rates, Lipolysis is when the fat cells break down into energy, and the fat oxidation rates is when the cells burn off this energy.
As your body absorbs the food, the insulin levels drop, this tells your body to begin storing the fat for energy and use it as fuel for the body, when all it absorbed the insulin levels are at baseline, and the body will start running off its fat stores.
Fasted cardio can increase muscle breakdown.
This type of exercise tears many muscle cells and your body might not be able to keep up with the repair, and this results in less muscle growth over time or even muscle loss.
Many people claim to have less energy and focus during workouts when training in a fasted state, but research shows that your body can adapt to training in a fasted state by modifying to use its glycogen stores more efficiently.
At the end of the day, exercising in a fasted state will not speed up your fat loss without a balanced meal plan according to your anabolic and catabolic stages that help preserve your muscle mass. While burning off fat but it can help with the latest stubborn areas and its essential to consume BCAA´s to keep the body from burning muscle stores because it can help preserve muscle as well as consuming fast absorption protein such as protein powder.
Some steps to take towards maximizing fatless are an aggressive calorie deficit, high protein diet, 3 to 5 hours of resistance training and keeping cardio to a minimum.