I have vivid memories of frequently going to McDonald's as a kid and enjoying a Happy Meal. My metabolism revved like a jet engine at that age, so almost anything that made it down my gullet was used as energy and not stored as fat. Nowadays, If I still at McDonald's as often as I did back then, I'd probably have a body like Grimace.

It's a natural -- though very unfortunate -- fact that our metabolisms tend to slow down somewhere around the age of 25. From there, it slows down by around five to ten percent with each subsequent decade that passes. Does this mean that you're fate is sealed and that you must accept your overweight destiny? Not at all.

By exercising regularly, you can keep your metabolism decline under a great deal of control. For the most part, if you get up and start moving every day you can very well increase your metabolism, or at least keep it to around a 0.3 percent drop per decade, says Dr. John Berardi, author of The Metabolism Advantage.