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Dieting and Metabolism
By WLR Dietitian
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When we're bombarded with images of gorgeous celebrities
who seem to lose weight in the time it takes us to eat a
Danish pastry, it's no wonder we're often tempted to cut our
already low calorie intakes in an effort to shift an extra
pound or two each week.
But surprisingly, rather than helping us to reach our
target weight more quickly, severely restricting calories actually
prevents our bodies from burning unwanted fat stores
effectively - and unfortunately, this means that weight loss
slows down.
Why does a very low calorie intake slow down weight
loss?
Quite simply, your body goes into 'starvation mode'. This
mechanism, which is thought to have evolved as a defence
against starvation, means the body becomes super efficient at
making the most of the calories it does get from food and
drink. The main way it does this is to protect its fat stores
and instead use lean tissue or muscle to provide it with some
of the calories it needs to keep functioning. This directly
leads to a loss of muscle, which in turn lowers metabolic rate so
that the body needs fewer calories to keep ticking over and
weight loss slows down. Of course, this is the perfect
solution if you're in a famine situation. But if you're trying
to lose weight, it's going to do little to help you shift
those unwanted pounds.
So how many calories should I have to prevent starvation
mode?
Unfortunately, there's no single answer to this question.
As everyone's metabolism varies in the first place, so too
will the point when the body starts to use muscle to provide
it with calories in a 'famine-type' situation. That's why WLR
works out suitable calorie intakes for each member on an
individual basis and never lets you opt to lose more than 2lb
a week, which would require a severely restricted calorie
intake. In other words, if you stick to the calorie intake
recommended by WLR, you can be sure your body won't go into
starvation mode.
As a general rule though, most nutrition experts recommend
never going below 1,000-1,200 calories a day if you're dieting
on your own. It's also worth bearing in mind that the body
doesn't suddenly 'enter' and 'leave' starvation mode, like
crossing the border from Devon into Cornwall. It's a gradual
process - so you don't need to panic if you do go below your
calorie intake very occasionally.
What's the link between muscle and metabolism?
The metabolic rate - the rate at which the body burns
calories - is partly determined by the amount of muscle we
have. In general, the more muscle we have, the higher our
metabolic rate; the less muscle we have, the lower our
metabolic rate. This explains why men, who have a high
proportion of muscle, have a faster metabolism than women, and
why a 20-year-old has a higher metabolism than a 70-year-old -
again, they have more muscle.
Ultimately, muscle burns a lot more calories than fat so
when we lose muscle, our metabolic rate drops and we burn
fewer calories. In fact, research shows that the body loses a
proportionately high amount of muscle with a very low calorie
intake and this may considerably suppress metabolism by up to
45 percent.
This explains why it's crucial to do as much as you can to
protect your metabolic rate, especially when you're dieting.
And this means dieting sensibly with a suitable, rather than a
very low calorie intake so that you lose fat rather than
muscle.
Is there anything else I can do to stop losing muscle when
I'm dieting?
As well as making sure you have sufficient calories to burn
fat rather than muscle, it's also possible to build muscle,
which in turn boosts metabolism. And the way to do this is, of
course, to increase the amount of exercise you do. While
aerobic activities such as jogging, swimming, fast walking and
aerobic classes help to tone muscle and burn fat, strength or
resistance training in particular will increase the amount of
muscle you have in your body. And this is good news because
for every extra 1lb of muscle you have, your body uses around
an extra 50 calories a day! This means an extra 10lb of muscle
will burn roughly an extra 500 calories a day without you
doing anything - and that's a sufficient amount to lose 1lb in
a week.
But doesn't your metabolism drop when you lose weight
anyway?
Yes, your metabolic rate naturally slows down a little when
you lose weight, but this isn't automatically because you've
lost muscle. It's because when your body has less weight to
carry around, it needs fewer calories. This means if you
weighed 13st to start with and now weigh 9st, you need fewer
calories to maintain your new weight than you did when you
were heavier. Simply put, there's 4st less of you to carry up
and down the stairs, into the bath, around the supermarket and
to the bus stop - and because your body doesn't have to work
as hard as it did in the past, it can survive on fewer
calories! This is why you should regularly update your Goals
and Results - as your weight drops, Weight Loss Resources will
recalculate how many calories you need to keep losing weight
at your chosen rate.
Will yo-yo dieting have damaged my metabolism permanently?
Fortunately not! The idea that yo-yo dieting permanently
lowers your metabolism has been relegated to the archives.
However, if you've frequently crash dieted and severely
restricted your calorie intake without exercising, it's likely
you'll have a lot less muscle now compared with the very first
time you dieted. As a consequence, it's likely your metabolism
will also be lower so that you need fewer calories to maintain
your current weight. This is because when you follow a very
low calorie diet, you lose muscle as well as fat (see above).
But when the weight goes back on, you usually only regain fat.
This means, your metabolic rate is likely to have dropped a
little every time you've dieted, making it slightly harder
each time for you to lose weight. The good news is you can
increase the amount of muscle you have by increasing the
amount of exercise you do. This in turn will rev up your
metabolism so that you can lose weight one final time on a
slightly higher calorie intake than you've perhaps been used
to.
For more on how to boost your metabolism, see my related
article, 8 Ways to Speed Up
Your Metabolism
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