Fat people tend to use metabolism as an excuse, when for most of us it's simply a matter of lifestyle. Our muscles hold and awfully lot of glycogen for later conversion into glucose, and getting out there and moving a lot will deplete those stores, which will be replenished from food before any fat is added. Folks think that just walking a lil bit won't help, but energy is energy. My car actually burns more fuel if I drive somewhere slowly, and so do my legs.
This is why I love low carb so much. You get your body in a state where it's always burning fat, even as part of the bmr.
That's just Nutrition 101, and it's not really my area so if someone hasmore insight into the system I'd love to read it.