the same thing goes for physical labor. Exhaling is mechanically how you lose body fat. Breathing more isn't sustainable without creating demand, but if it were sustainable you could just breath faster to lose weight.
Out: CO2
That extra C atom comes from your metabolism. If you're in a calorie deficit, it has to come from your C atom reserve storage.
That's a way of saying that breathing faster won't burn more fat just because of the breathing: burning fat is a bit more elaborate than that.
Which is wrong, since breathing involves pumping air with your muscles.
Yes, and that will be your muscle mass as well as body fat if you're not exercising and maintaining a decent protein intake.