Insulin quiet = maximum lipolysis. Insulin higher = blunted lipolysis.
Meatheads chugging tons of insulinogenic BCAA/EAA (leucine has a response to damn near glucose), spiking insulin right before "fasted cardio" = hilarious. You won't eat up muscle that easy. This is marketing bullshit.
I think doing cardio fasted is fine. It's not catabolic if your daily macros are in check (hitting your protein). But I think being fasted is sometimes overstated in terms of importance. What you eat all day still trumps whether or not not you did fasted cardio or not. Your EPOC and calorie deficit for the whole day matters more than that fasted cardio window.
Fat loss is very simple. Get in a calorie deficit. Eat less carbs to keep insulin levels lower continuously. Doing it with diet versus tons of your cardio its not only easier but will break down less tissue.
AAS and adequate protien intake during this time preserve lean muscle mass.