HIIT is anaerobic. At levels beyond 70% of max heart rate, the pathway is not sufficient to burn bodyfat during the intense exercise. The body will burn mostly glucose. If there is none available the body will make it itself via gluconeogenesis, and that's where it takes it from protein in muscle tissue. There is an HIIT aferburn effect, but if you're on low carb, your best bet to minimize muscle loss is to do steady stream cardio, at levels below 70% max heart rate. I've seen far too many people over the years make the mistake of doing HIIT such as Insanity on ultra low carb diets, and then end up looking like smaller, flabbier versions of their former heavier selves, because they sacrificed too much muscle tissue in their quest to lose 'weight'.
Most people who do extremely low carb, don't increase their fat and protein intake enough. HIIT is anaerobic, Insanity and the other BeachBody garbage is just aerobic, and burns muscle tissue like
crazy. Never heard of anyone in BeachBody doing extremely low carb diet. Their crappy shakes and all their other products are loaded with carbs, and BeachBody is a MLM scam. I full tilt sprint at top speed. I'm not burning muscle tissue, as I eat plenty of protein. Gluconeogenesis is not a bad thing, as it is also a healing, and muscle cell replacing process, that gets rid of old and damaged muscle cells.