When it comes to exercise, the body mainly utilizes fats and carbohydrates for fuel. While it is true that these fuel sources are utilized in different proportions depending on the intensity of the activity chosen, the reality is when it comes to weight loss it doesn’t matter what kind of fuel you use. What it boils down to is the number of calories you burn versus the number of calories you consume.
The flawed notion of a "fat burning zone" was derived from the fact that the body uses fat as primary source of fuel when exercising at lower intensities, which is true. However, the idea that there is a “fat burning” zone one should exercise in is a bit misleading, as ultimately you could exercise at a higher intensity and burn just as many calories from fat, if not more, even though the body uses carbohydrates as a primary source of fuel during higher intensity efforts.
All in all, when it comes to burning fat, a well-rounded, consistent approach to exercise is key, as the more calories you burn, the more fat you burn.