Diet + weights + cardio = success.
I'm currently on a keto diet, lifting 4 days a week and 7 days a week low intensity cardio. On my lifting days I will do 90-120 minutes weights, followed by 60 minutes low intensity cardio. On my rest days I will do 90 minutes low intensity cardio twice daily. The key to fasted cardio is to do low intensity. This way you are burning majority of calories from fat and not from other sources. This way you wont loose muscle
keep it up!