If your body is converting muscle into energy when you do cardio, you should probably speakbo a doctor.

That's like absolute last resort survival mechanism so that you can find food when you are starving to death.

You don't want your muscles being cannabibalisd for energy.

I'm diabetic and if I don't take insulin for long enough i suffer from this, my fat and muscles will start to cannibalised after a couple days of not taking insulin.

It's not something you want to happen at all.