I really didn’t want to argue with anyone on this subject here, but this is just simply not true. You want your body to be very efficient at burning both fat and carbs. With proper endurance exercise and diet manipulation, this is possible. Do some long days on low glycogen to help with fat metabolism. Do some hard intervals/muscle endurance workouts fueled with carbs. Balance is key. But if you neglect the burning carbs, your body actually will not produce the proper enzymes for outputs where carbs are required, and if you are that fat adapted, having carbs can actually cause increased muscle acidosis compared to someone with a balanced diet/metabolism. There’s a very interesting podcast about this on Science of Ultra, i believe it was the “fat adaption” with Louise bourke.
I will agree that fasting does pose some benefits depending on training level and the like. When I’m working full time and not training >3hrs/day, I’ve always liked the fasting. Or at least carb backloading. There is some research out there that shows that people on equal calories, but heavily loaded carbs in the evening vs having carbs in the morning showed less overall weight loss but more overall fat % loss. So we really need to define our goals with regard to weight loss and such. Do we want body composition change, or do we just want to lose weight? A more positive body composition change goal could benefit more from an intermittent fasting, carb backloading type diet. Someone who just wants to lose weight, then it’s just a simple matter of calories in/calories out. There’s no secret diet for pure weight loss, it’s really is just kcal in/kcal out. Doesn’t matter if it’s Reese cups, keto, vegan, Mediterranean, fasting, whatever. Consume less than you burn and you lose weight. End of story.