The main purpose of breathing is not to move air, but to move energy.
The Chinese have known about this vital human energy for centuries. To this day, the Chinese believe that all illness is caused by some blockage in the chi. Millions of them (and I hasten to point out that you don't see many fat Chinese) arise at dawn morning after morning to practice " Qi Gong," a form of exercise that focuses on breathing. The Indian yogis had a different name for it (prana), but it's basically the same thing. Energy and the key to harnessing it is your breath.
You have this incredibly powerful force and you're not using it. You're not capitalizing on this almighty life force that's certainly a lot bigger than your wimpy weight problem. The other thing you should understand is that your body itself is energy. A lot of us believe our bodies are static matter, frozen statues. But physicists tell us it just ain't so. Our bodies are rivers of energy -- constantly changing, continuously flowing.