What exactly is metabolism?

"It's the sum of the processes by which we convert food into usable energy," says Richard Ho, Ph.D., a research fellow who studies the relationship between metabolism, exercise, and diabetes at Harvard's Joslin Diabetes Center in Boston. On the face of it, metabolism appears pretty straightforward: It's basically the body's "engine" – the way your body creates the energy it needs to move and even to think. But a host of issues - most notably, genetics (remember your lucky friend?) and lifestyle - have effects on an individuals metabolism. Many factors affects how "efficient" a fuel-burner your body really is. Your individual metabolism, your engine, will differ from another person's depending on your genetic background, what you eat, your sex, your age, how much muscle you have, and how much you exercise - among other factors. Now, the really tricky part: The more efficient your metabolism is, the more likely you are to carry more weight. Yep, you read that correctly: A car that's "'fuel efficient" doesn't burn as much gas as a 16-cylinder Ferrari. Likewise, an efficient metabolism doesn't require as much fuel to be burned as an inefficient - the Ferrari - metabolism. Your car may be a Honda Accord; your skinny friend is a Ferrari. The fuel your put in your "tank" and don't burn? To extend the auto analogy, it just stays in the tank—or, in this case, on your hips.

How finely tuned is our metabolism?

Think about this: the average weight male consumes about one million calories per year A change of a mere 3% in energy intake (Ei) or energy output (Eo) will result in 10 pounds of gained weight in a year.To remain at a stable weight, imagine the finely-tuned controls that must be in action to intake and burn a million caloaires of food per year - the equivalent of 1000 pounds of fat tissue - amd not gain weight. The weight gain that occurs after age 40, which is normally about a pound per year, can be attributable to a decline in our resting metabolic rate (RMR), probably due to loss of muscle tissue.

How do I determine if my metabolism is "fast" or "slow?"
The only way to know with scientific precision, is to have your basal metabolic rate (BMR)—or, the rate at which you burn calories when you're at rest, such as when you're glued to the tube watching American Idol©. It is a test performed in a very special room and requires precise measurement of your oxygen intake and output of carbon dioxide. But even then, it may not tell you anything specific or helpful. Your individual BMR can vary from week to week and month to month. In addition, it's just one small piece of a very complicated puzzle that contributes to why some people have a hard time losing weight. It's absolutely not a number you should get hung up on.

What role does exercise play in metabolism?
Exercise is one of the two parts of the energy equation (the other is food) over which you have control. Don't forget: burning calories creates energy for your body. Your body burns more than half of the calories it uses on a daily basis simply to keep your organs functioning and your temperature regulated. Another chunk of calories, about 10% of what you take in, gets used up digesting food and converting it to energy (called the "thermic effect of food"). The last 20% or so gets used—or not used—depending on your activity level. If you exercise for 30 to 60 minutes most days of the week, your body will require more energy - which means it'll need to burn more calories—than if you spend your free time sitting in front of the TV. So, when all is said and done, you have control over about 20% of the food calories you take in.

I have a short amount of time to work out, what should I do—aerobic exercise or strength training?
Why not both? Generally speaking, aerobic activity burns more calories and keeps your metabolism elevated for a longer period following exercise than strength training does. So if you want to burn more calories in a given week, you're best off spending the bulk of your time walking, running, rowing, or doing aerobics or some other form of aerobic exercise. But that doesn't mean strength training won't improve your metabolism, also. Research has shown that performing a standard, 10-exercise weight-lifting routine in 20 minutes "only" burns about 100 to 120 calories. But trading 10 pounds of fat for 10 pounds of muscle through resistance training (weight lifting) increases your BMR by over 100 calories per day, every day. Conclusion: If you have 30 minutes to exercise, your time is best spent exercising both ways - aerobic and anaerobic (strength training). How about 20 minutes of brisk walking and 10 minutes with some exercise bands or doing push-ups and sit-ups? Better still, do a 30 minute walk with 2 pounds ankle weights and 5 pound wrist weights. Swinging your arms briskly and lifting your legs higher for last 5-10 minutes are guaranteed to build calorie-burning muscle.

Can eating certain foods really boost my metabolism?
Yes, they can. Remember, one way we burn calories without even trying is by digesting what we eat - the thermic effect of food. And the body processes different foods at varying rates and with varying amounts of effort. For instance, protein, made up of amino acids, requires more energy to digest than fat and a lot more energy than simple carbohydrates (potatoes, pasta, and white bread). For example, getting at least 30% of your daily calories from protein will boost your metabolism by as much as 150 calories a day. Another example: Raw foods require more energy to digest than cooked foods, because your body essentially has to "cook" the food by breaking it down. So while foods, such as vegetables, fiber, whole grains, and protein, that take more energy to digest may not force your BMR up for 24 hours, your body does burn more calories just by having to digest these type foods. An added benefit is that high-fiber foods like whole grains and proteins generally make you feel more full for longer periods of time, which may make you snack less often.

Is it true that constant dieting can slow my metabolism?
Absolutely, positively, yes!. When you lower calorie intake, you don't just lose your unwanted fat; you lose valuable muscle tissue as well. And since muscle requires more energy just doing nothing, your BMR drops lower and lower with every pound of muscle tissue lost. Furthermore, in response to chronic dieting, your body's metabolism becomes more efficient. As you lose weight, your body reacts as though you are starving, and it produces starvation hormones, which slow down your metabolism. Back to the car analysis: chronic dieting (starvation) causes your Ferrari to become more and more like a Honda. There are three ways to keep your motor firing on all cylinders even when you cut back on food intake (diet):

1. The most obvious way is to prevent muscle loss by actively and regularly maintaining your strength-training routine
2. The second is to keep your metabolism fired up by eating several small meals throughout the day, so that you are constantly burning calories through digestion.
3. Lastly, get your protein in. A good rule of thumb for those moderately overweight is grams of protein equal to half your body weight.

Can dietary supplements touted as "fat burners" really speed up my metabolism?
They can—but only the littlest bit, and only temporarily. Worst of all, they risk your good health. Products that contain caffeine, including green tea, do slightly increase a person's metabolic rate. But they also increase your heart rate and blood pressure.For the tiny benefit your may receive. It's not worth the risk. Fortunately, the FDA removed - ephedra - the only significantly active ingredient in over-the-couter "diet supplements a few years back. The rule has banned the sale of supplements containing ephedra. But those based on green tea (Relacort™ and Cortislim™ among others) are also suspect.

Does metabolism slow with age?
Unfortunately, yes. And for women, who naturally carry more fat than men, the effects are particularly dramatic. When women lose muscle due to decreased activity and with age, we lose proportionately more of it than men, because we had less muscle to begin with. By some estimates, a woman's BMR drops by as much as 25% with menopause, mostly due to the decrease in muscle mass. This is an issue that women should be aware of in their 20s because if you're 50 years old and you've exercised for 20 or 30 years, especially if you've spent those years doing some strength training, you've got a lot more muscle mass - and a higher metabolism - than the woman who didn't start exercising until she was in her 40s. Then again, it's never too late to build muscle—and increase your metabolism. So instead of getting hung up on your current BMR and focusing on whether it's fast or slow- pondering, say, whether you've got yourself a Honda Accord or a Ferrari on your hands – why not just start your engine and get moving?