I found this great article on Webmd.com
Your brother inhales pizza three times a day and never gains a pound, while you watch your carbs, calories, and sweets and still haven’t lost an ounce. He must have a fast metabolism, you decide, while you seem to be cursed with a slow metabolism. Should you throw in the towel and forget about dieting?
No, say the experts. Your metabolism may be slow, but it’s not all your genes’ fault. And being fat is not your fate. Everyone — no matter how old, overweight, or out of shape — has the power to increase his metabolism. Here’s how:
Simply put, metabolism is the process of breaking down proteins, carbohydrates, and fats to yield the energy your body needs to maintain itself. The rate of your metabolism depends on the interaction between the number of calories you consume, the number of calories you burn while eating and exercising, and the calories you burn based on your individual genetic makeup.
How can you increase your metabolism? Well, there’s not much you can do about your genes (they only account for a measly 5% of total daily calorie consumption anyway), which means the best way to rev up your metabolism is to increase your body’s need for energy.
“Your body can burn calories from either fat, protein, or carbs,” says John Berardi, PhD, CSCS, president of Precision Nutrition, and author of The Metabolism Advantage. “Of course, you’d rather it burn fat calories, but your body isn’t wasteful; it will burn fat only when it needs energy.”
One such time is during exercise, but it’s difficult to exercise all the time, especially if you’re stuck at a desk all day. Luckily, your body requires extra energy at other times, too, such as during the first hour or two after intense exercise like interval training and weight lifting. This is called the “afterburn” effect, Berardi says, and it can last for up to 24 hours. Strength training with heavier than usual weights uses up energy, too — in order to repair small (healthy) muscle tears.
And simply being more muscular boosts your body’s energy needs. Each extra pound of muscle you carry can burn up to 50 additional calories just to maintain itself — and with no effort on your part. You can also increase your metabolism by eating foods that require extra energy to digest and metabolize; for example, protein. Your body burns twice as many calories digesting high-protein foods as it does foods that are high in carbs or fat, he says.
How Age Changes Your Metabolism
It’s true; your metabolism does slow down with age, but keep reading — the news isn’t all bad.
Starting at about age 25, the average person’s metabolism declines between 5% and 10% per decade, Berardi says, which means that the typical North American loses between 20% and 40% of their metabolic power over the course of their adult life span.