The inside scoop on your metabolism

You probably have a vague notion that your metabolism is a key player in whether or not the calories you take in stick around where you’d rather they didn’t. You probably also have a friend who’s white-hot internal furnace you credit for the contradiction between their lean physique and supersized appetite. But aside from notions about ‘revving it up’, what’s going on in there? What determines how fast your engine burns what you feed it? And how do the miles on your feet and the food on your plate affect your metabolism? Here’s your insider’s guide to what’s going on inside