There are lots of articles on the fat burning zone but the one below explains the problem with it.
Without going into a thesis, I am going to tell you the TRUTH!
The Truth is you burn more overall calories and are much better off doing intense intervals. Do these intervals to your capacity though. Do not put to much stress on the body.
Basically, I think the “FAT BURNING ZONE” has caused many people to remain fat. Focus on increasing intensity, getting stronger with short intense workouts.