Well, in order to efficiently lose weight, you have to gain some muscle, muscle burns fat, now as for fasted cardio, while in theory it makes sense, personally to me it makes more sense to burn calories you've put in your body throughout the day, the key to loosing weight is to create a deficit between calories burned and calories taken in that day. I like to workout at different times throughout the day, that way my body has to work hard at different times and it does not get used to one time.