With all due respect I do not believe this to be correct.
It's easy to determine what your fat burning zone is by doing a VO2max test eg with a CardioCoach. When your body consumes oxygen it's aerobic burning fat which is easily measured using a mask on a treadmill. Anaerobic exercise is all sugar burning. In long distance triathlon we train heavily to increase our base aerobic thershold to burn fat.
The science of fat people vs not fat people has many factors but you can't argue with hard science eg how is your body operating and doing with the oxygen or running without oxygen intake but putting out more watts on the bike or treadmill.
Even Ted Naiman really says the same thing as everyone agrees you burn 1) glycogen first 2) sugar next ALWAYS when anaerobic because there's not enough time for your body to get enough oxygen to burn fat. So the theory is you need to train to burn fat by doing long bouts of low intensity exercise. This actually is NOT necessary because there is always a period when your body could be burning fat eg when you are sleeping or sitting around doing nothing (your BMR). It's pretty well understood if you have sugar available, you will burn it first and if it's not needed, your body will release insulin and then it converts it to fat. If you burn all your glycogen and all the sugar then your body has no choice but to burn fat. People think you lose muscle mass but this is also not correct. You burn glycogen which is stored in your muscles and you lose 3 grams of water for 1 gram of glycogen so lose a lot of water weight but this all stops after you burned that 2000 calories. You hit the wall, slow down/stop and you are now burning fat because you have nothing else to burn. Until all your fat is gone does your body start breaking down protein in your muscles but you're consuming 60 grams of protein anyway to replenish and prevent this from happening.
You might be more hungry and therefore eat more and therefore not lose weight or burn fat but if all you eat is powdered whey protein and gatorade endurance as I propose you have choice because there is nothing else available to snack on besides dirt. I guarantee anyone that sticks to the 720 calorie diet of 50 carb/50 protein while travelling 25 miles a day will lose fat. Again you have no fridge to run to as the only thing in your pack is powdered protein and sugar so perhaps you're miserable but you will survive and you will burn your fat reserves.
I calculate I can carry an entire's day worth of food (3 whey protein, 2 gatorade endurance) in 208grams including packaging. That's 3.2 lbs of food for an entire 7 days which is hard to beat.