Rev Up Your Metabolism to

You used to eat anything -- and everything -- and not gain an ounce. Now it seems that just looking at a Krispy Kreme packs on another 10 pounds. You shrug your shoulders and say, "I'm getting older. My metabolism's not what it used to be."

You may be right (like it or not, your metabolism does slow down as you get older), but does that mean you have to live with it? Not necessarily. There are things you can do to rev up your metabolism, say nutrition experts -- just as there are things that won't work at all.

Simply stated, your metabolism is the way your body burns up all of the calories from the food that you eat, says Tammy Lakatos Shames, RD, LD, CDN. It's a complex process that includes all of the chemical reactions that take place in your body to keep your organs working and to keep you alive.

The speed at which your body burns up calories is called your metabolic rate, says Shames, who with her twin sister, Lyssie Lakatos, RD, LD, CDN, is the co-author of the forthcoming Fire It Up! 200 Simple Ways To Jumpstart Your Metabolism and Lose Weight Forever. Your sex, height, weight, genetics, age, lifestyle, and body composition affect your metabolism. Your metabolism plays a significant role in weight management: The faster your metabolism, the more calories you'll burn, and the less likely that you'll be overweight.

Here are 7 "dos" and don'ts" for revving up your engine. For more advice about metabolism and weight loss, sign up for the Weight Control newsletter

1. Don't fall for "fat-burning foods."

Can certain foods -- such as celery and grapefruit -- help you lose weight? Not so, say Shames and Lakatos. "Celery is low in calories and has a good deal of fiber, but it doesn't speed up your metabolism," says Shames. As for rumors that grapefruit increases your body's ability to burn calories because of its acidity, there are no studies to substantiate that myth. "In fact, if you were to eat the same number of grapefruits as any other fruit, such as peaches, or oranges, you may actually be more likely to gain weight from eating the grapefruit, as they are slightly higher in calories (due to their larger size)," says Lakatos.

2. Don't fast or skip meals.

The idea that fasting or skipping meals regularly is a great way to cleanse the system of impurities, speed metabolism, and encourage weight loss is just another myth, says Sue Ayersman, a certified clinical nutritionist (CCN) at Kronos Optimal Health Centre in Scottsdale, Ariz. "Your body needs a certain amount of calories and nutrients each day for normal function," says Ayersman. "Denying the body of these essential elements throws the system into survival mode, slowing metabolism and encouraging the storage of energy in the form of fat. You have to eat in order to lose weight." Four to six small meals a day is a good way to keep your metabolism humming.