It provides a convenient scapegoat, our metabolism. Some days, the mysterious biological process seems to provide the only explanation for why some people can burn off breakfast by running errands while others have calories that never truly vanish. Unfortunately, the metabolic reality appears to be complex and likely a bit frustrating.

 

   Granted, the success of your battle with your waistline in 2009 rests largely upon basic math: Do you eat more daily calories than you expend? Still, some factors beyond your control, including age and genetics, may unfairly stack the metabolic deck. "Some people are naturally gifted in that they have a higher metabolism than other people," says Tara Gidus, an American Dietetic Association spokeswoman.

 

   The intriguing and hotly debated question is whether or not you can tweak your metabolism, at least to some degree. How many hours you sleep, how much muscle mass you maintain, how frequently you eat -- all may play a role, according to some researchers and clinicians. Even how much you putter around the house and yard may contribute.