And I believe EVERYTHING I read on the Internet.
Here is how it goes. If you're aerobic then your mitochondria are using oxygen to burn fat (virtually unlimited supply). If you're anaerobic you have outstripped your body's aerobic ability and instead of burning fat you are burning sugar (limited supply). So we need to develop our aerobic capacity in order to reduce fat and empower our bodies to go long distances.
I learned today road riding that the aerobic zone is a very low heart rate. Much lower than we are accustomed to when mountain biking. We need to slow it down. This will burn fat (instead of sugar) and develop improved aerobic capacity. Remember, LSD.