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 specialised 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.
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 really the 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 your lean body mass. Imagine that your body is divided into two parts: one part
is your fat, and the other part is your lean body mass (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.
Your age
As you age, there is a tendency to lose some muscle mass.
Natural hormonal changes contribute to some loss of muscle mass. Furthermore,
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 weight.
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 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.
Written by Susan Bowerman
MS, RD, CSSD. Susan is a paid consultant for Herbalife.
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