This is just conjecture but I wonder, if it takes 8 hours to replenish glycogen stores from the food you eat keto or not and maybe 3 hours of exercise to burn up all your glycogen compared to fasting. Depleting glycogen stores makes the body burn real fat?
This is not for the faint of heart (if you don’t like hardcore weight loss?):
I like to take real cold showers or ice baths (use caution; amount ice tolerable levels; does not take very much) after cooling down from a HIIT work out (15 to 20 min.) with a higher extra virgin omega 3 intake and a little drinking water with bitter melon extract in it does the trick for me. Cold Thermogenesis CT exposure depletes glycogen stores very rapidly. You can literally eat anything you want and still be in ketosis. Caveat for CT cold adaption: I usually start out dunking face in ice water just to get my body use to the idea of a cold shower or ice baths (hormesis).
 “…Well, the body simply pulls energy out of the ‘fridge’. Since you have enough glycogen stored up to last over 24 hours on a regular day, you would need to do some serious exercise for a long time before you could exhaust those stores. Endurance athletes occasionally do hit this ‘wall’, where glycogen stores run out. …” …More
 Glycogen shortage during fasting triggers liver–brain–adipose neurocircuitry to facilitate fat utilization
 “…Fasting, low-carb diets, high intensity exercise, and cold thermogenesis can all use up and burn off glycogen in the muscles. Once depleted, the muscle is primed for glycogen supercompensation. If one eats carbs during this time, they can refill, to higher-than-normal levels, their glycogen stores. This results in higher muscle protein synthesis rates and fuller, stronger muscles that perform at peak capacity.
The Cool Fat Burner has been shown able to burn off glycogen at a rate comparable to exercise, and to accelerate acquiring the ketogenic state. In the “Body Recomp” experiment, Eric G. was able to eat hoagies, bowls of cereal, and other large amounts of simple carbs, yet stay in ketosis. This demonstrates the massive potential to set up a huge glycogen supercompensation. As shown in the “Body Recomp” experiment, this not only allows for glycogen supercompensation and thus boosted muscular growth and performance, but in practical terms, it allows for much more frequent carb refeeds and cheat meals! …” …More