The Respiratory Exchange Ratio is the ratio of the Carbon Wildfit Dioxide produced to the Oxygen consumed to provide energy to the body. The burning of fat to provide energy has a RER of 0.7, for each molecule of oxygen consumed 0.7 molecules of Carbon Dioxide is produced. Burning carbohydrates for energy produces . molecule of Carbon Dioxide for each molecule of Oxygen used, hence a RER of .. When exercising, the more intensely you exercise the more energy you require and the more oxygen you consume.
When exercising at a lower intensity your RER is lower, closer to 0.7 which allows your body to use your body's fat stores for the energy required. At higher intensities, your RER tends closer to . and carbohydrates are the only way to provide the energy that the body requires. At lower intensities, your body takes more energy from fat stores which has led to the creation of the fat burning zone. Does the amount of calories burned from fat during exercise matter. I believe not, a calorie burned is still a calorie burned.
You burn body fat by consuming less calories than your body requires. Weight loss can be achieved by a reduction in calorie intake from food, or an increase in your body's energy requirement (increased muscle mass or increased energy expenditure). Many people do not want to, or do not have much time to spend exercising. From this point of view, performing high intensity workouts will burn the largest amount of calories in the shortest period of time. However, whenever starting out any new training regime, you must progress into it.