What is this mysterious process called metabolism?  And once you know what it is, how can you keep yours pumped up and primed for fat-blitzing action?  Metabolism is the rate at which your body burns calories, and diet and exercise each play a key role.  But you can also blame a slowed metabolism on other things - like your couch-slouching habits or even your genetics. Whether your goal is to lose a few pounds or stave off love handles, you must continually stoke your metabolism to keep it in high gear.

 Here are 5 strategies you can start using today to make over your metabolism right now.  

• Know your Numbers  Metabolism is controlled by three different factors. The thermic effect of feeding (TEF) accounts for 5-10 percent of the calories you burn all day. This refers to the amount of energy your body must expend to break down the veggie burger or spaghetti dinner you ate last night. The thermic effect of activity (TEA) makes up about 20-30 percent of calories burned daily and refers to the number of calories you expend during physical activity, from hauling groceries to going for a three-mile run. Finally, and most important, your resting metabolic rate (RMR) refers to the number of calories it takes to maintain the body's basic functions - pumping blood, blinking your eyes. It accounts for the lion's share (60-70 percent) of expended calories. It's when RMR declines that you have the hardest time fighting a battle of the bulge.  One problem: "RMR decreases as we age," says Stephen Farrell, Ph.D., associate director of the division of continuing education at the Cooper Institute for Aerobics Research in Dallas. "That's partly due to the fact that we often become more sedentary as the years pass." But a sluggish RMR can also be blamed on diet - especially a stringent one.  "If you severely restrict the number of calories you consume, RMR may temporarily drop," says Daniel Kosich, Ph.D., author of Get Real: A Personal Guide to Real-Life Weight Management (IDEA, 1995).  The more calories you slash when you start to diet, the harder it is to lose body weight. Lisa Dorsey found this out the hard way.  A history of eating very low-calorie meals had plunked the 33-year old New Yorker's metabolism into slow drive.  "I was eating 1200 calories a day and doing six hours of cardio a week - and I couldn't lose a pound," she recalls.  "My metabolism was literally limping along." Blame this downshift on an inherent defense mechanism. "When there's less fuel available, your body thinks it's in famine mode, so it burns fewer calories," explains Louis Aronne, M.D., director of the Comprehensive Weight Control Program, affiliated with New York Presbyterian Hospital. "Another problem with deprivation diets is that you may lose weight at first, but you'll also lose lean muscle," adds Tierney Vaughan, fitness program manager at the Sports Center at Chelsea Piers in New York City.  One pound of muscle can burn up to 50-60 calories a day (compared with fewer than 10 calories per pound of fat).  So if you lose five pounds of muscle due to strict diets or inactivity, you eventually sacrifice the potential to burn an extra 250-300 calories a day.

• Eat More Often   To turn up the burn, start with small changes. "Don't do anything drastic or you could trigger a counterproductive response," says James O. Hill, Ph.D., professor of medicine at the University of Colorado Health Sciences Center in Denver. Consuming smaller, more frequent meals may boost metabolism.  "If you take in the majority of calories in one or two meals, there's a tremendous surge of insulin to the bloodstream, which sends a message to store calories as fat," says Dr. Aronne.  Eating smaller meals more often may make the insulin bumps less jarring.  But watch portion sizes!  "People tend to underestimate their intake by 400 to 500 calories a day," says Kosich.  To track your eating habits, he recommends writing down everything you eat in a journal.

• Choose Your Protein Sources Carefully   The type of food you eat also makes a difference. Some nutrients, like protein, have a higher energy burn than others. Given the chemical structure of food, your body actually uses more calories digesting a skinless grilled chicken breast than an equivalent serving of pasta. Remember, though, that many high-protein food sources come in a high-fat package. Keep proteins at 10-15 percent of total calorie intake and look for leaner proteins such as white-meat fish, poultry, nonfat yogurt and legumes.

• Boost Fiber Intake   Eating more fiber makes the digestive process more efficient and keeps your blood sugar levels steady throughout the day.  "Most people think that they are getting enough fiber in their diet, but they aren't," says Vaughan.  In order to ensure that you reach the recommended 20-35 grams of fiber per day, consume plenty of whole grains, leafy greens, wheat breads, beans and fruits.  

• Outsmart Your Genes   Even if you follow a healthy diet and perform regular cardiovascular exercise, you may still face another challenge - your genes.  Some scientists speculate that our bodies may gravitate toward a preprogrammed weight known as a set-point. Try to get below that weight and the body battles to push those numbers up again. The good news:  You can change your metabolic destiny.  One solution is to spend more time lifting weights, which will increase that crucial calorie-burning muscle mass. "If you build enough lean muscle, you'll burn so many more calories in a day that your body will have to lower its set-point," says Vaughan. Bonus:  Weight lifting keeps metabolism revved for hours after a workout. In fact, recent studies show that weight lifters continue to burn calories up to 15 hours after they have exercised, while most strictly cardio participants experience little (or no) after-burn effect. For proof that these simple strategies can work, just ask Susan Moultrie, 34.  When she moved to New York, her lifestyle changed dramatically - and so did her metabolism. Instead of playing tennis or hiking in her free time, the music executive crashed on the couch after a head-banging day in the office. Her weight ballooned 40 pounds, her self-esteem plummeted and she stopped exercising altogether. But simple changes gave her RMR a jump start. She began exercising again and incorporated weight lifting into her routine.  She stopped skipping meals and added low-fat snacks to her diet.  She's lost all 40 pounds.  The key to her - and your - success?  Make slow, smart changes and transform your life.  

"FITNESS"  Magazine - March 1999