Fat Burning Zone

In my opinion exercising into the 'fat burning zone' is both counter productive and a total crock! If loosing weight was as clear-cut and black and white an issue as some people try to make it sound there would not be any problem with overweight people. You hear 1 expert extolling the virtues of exercising into the 'fat burning zone' of 20+ minutes of vigorous exercise and another saying that you have to exercise at least 45 minutes to change the set point of your metabolism, others say 20+.
I don't claim to be any kind of expert but I have been reading everything I could get my hands on as well as seeing what worked for me. What I tend to believe from that combination is that you probably do need to do moderate exercise for 20-45 minutes but scattered throughout that time period you need to intersperse 5-10 minutes of intense exercise in 1 or more sets. I believe that the 20-45 minutes should be no more frequent than every other day & vary in length because the body is designed to respond to real life not some artificial program. Even if you are really running for your life you would not be running full out for more than a few minutes not a half hour +. But if you are not exercising for more than a few minutes once in a while there would not be any incentive to change metabolism set points. 'Fat burning zones' next time.