Physical activity helps metabolism - not sure why, though.

1 way to speed up METABOLISM with out a doubt... Building Muscle.

1 pound of muscle burns 50 calories a day while 1 pound of fat burns 1 calorie. now to build muscle you have to eat more unless you have a lot to work with (body fat). and once you build muscle the muscle will use the nutrients in your body and burn more calories. think of yourself as a fire and the more muscle you have think of that as more wood in the fire and you burn more. this is why huge men can eat more than women, and also why muscular men can eat so much without getting fat and stay swole and cut.