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| Written by Susan Bowerman, MS, RD, CSSD |
We hear a lot about metabolism – and often blame a ‘slow metabolism’ for our inability to keep our weight under control. Find out what factors affect your metabolic rate – and what can you do to change it. When patients tell me their weight problems are due to a “slow metabolism”, I think they truly believe that their bodies simply burn calories at a slower pace than other people’s bodies do. In their minds, if they only they could speed up the process, their weight problems would be solved. But what is “metabolism”, exactly? And – more importantly – is there anything you can do to change it?
Truths and myths about metabolism
In truth, your body weight and your metabolic rate are linked – but perhaps not in the way you might think. Simply stated, the term metabolism refers to all the chemical processes that your body undergoes every day in order to keep you alive. When your body converts the calories in your food into energy, or manufactures specialized chemicals that your cells need in order to do their job – those are metabolic processes. These processes your body performs every day – hundreds of them – make up your “metabolism”.
I can see how the term metabolic rate could confuse people. When you hear the word “rate”, you might think “speed” or “tempo” – so, it’s reasonable to assume that metabolic rate can only mean how fast (or slow) your body performs its work.
In reality, though, your metabolic rate (or, more accurately, your resting metabolic rate)refers to the number of calories you burn during a 24-hour period just to keep your body’s most basic processes going – processes like pumping blood, or breathing.
Of course, this isn’t all the calories you burn in a day, but your resting metabolic rate accounts for a sizeable chunk – about 75% of total calories you use up every day are used simply to keep your body ticking. Most of the remaining calories get used up during your daily activities and bouts of exercise.
What factors influence metabolic rate?
Some people’s bodies use up more calories to perform these basic metabolic processes than others (you might think they have a “fast” metabolism). And for those who seem to require very few calories, you might think their metabolism is “slow”. But now that you know that your metabolic rate isn’t really about how quickly you burn calories – it’s reallythe number of calories you burn each day – you can’t technically make your body burn calories any faster.
But, let’s look at what affects your metabolic rate in the first place – it will give you a better sense for what you can and can’t do to change it.
Your body size
Larger people have higher metabolic rates than smaller people do, and this is due largely to the simple fact that they just have more cells – each of which is doing some metabolic work. That’s one reason that men usually have higher metabolic rates then women – they just tend to have bigger bodies overall.
Your body composition
A very important factor in determining your metabolic rate is the amount of lean body mass you have. Imagine that your body is divided into two parts: one part is your fat, and the other part is your lean body mass (in other words – everything else that isn’t fat like bone, fluids, organs and muscles). This lean body mass determines your metabolic rate because every pound of lean mass you have burns about 14 calories per day (or about 30 calories per kilogram) – while a pound of fat only uses up about two. Muscle cells have a lot more machinery that converts calories into energy than your fat cells do. So, it makes sense that as your muscle mass increases, so would your metabolic rate, since – metabolically speaking – your muscle cells are very active.
Your age
As you age, there is a tendency to lose some muscle mass. There are couple of reasons this happens. For one thing, natural hormonal changes can contribute to some loss of muscle mass. And, the muscle damage that results from everyday wear and tear isn’t repaired quite as quickly as you age – and that can contribute to some muscle loss, too. With fewer muscle cells overall, you can’t help but burn fewer calories over the course of the day.
Your gender
Men have higher rates than women do for two simple reasons. They tend to be larger overall, and they tend to have more muscle mass than women do.
Cutting your calorie intake too much
It’s true that when you cut your calorie intake too much, your metabolic rate can take a dip. This makes sense if you think about it – your body is just trying to do the same metabolic work with fewer calories in order to keep you alive. But, in general, these decreases are relatively small, especially if you make modest – rather than dramatic – decreases in your calorie intake as you attempt to lose.
So, what can I do to boost my metabolic rate?
Now that you know what factors affect your metabolic rate, what can you do about it?
- Eat enough protein. Your body uses the protein you eat to build and repair muscle tissue. If you don’t consume enough protein in your diet, your body simply doesn’t have the raw materials it needs to manufacture and repair your muscle cells.
- Build muscle mass. This is probably one of the most important things you can do, since building muscle will increase the amount of lean body mass you have – which increases your overall resting metabolic rate. And, don’t think strength training is only for the younger set – with the right diet and proper exercise, your body is capable of building muscle at any age.
- Increase your daily activity. Any activity, of course, burns calories – but that, in itself, doesn’t affect your metabolic rate. But, when you exercise, you are using your muscles to move your body – and that helps to preserve your lean body mass. And, bumping up your activity can also help to offset any dips in your metabolic rate as a result of cutting your calorie intake.
