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we hear about calories all the time how
many calories are in this cookie how
many are burned by 100 jumping jacks or
long-distance running or fidgeting but
what is a calorie really and how many of
them do we actually need calories are a
way of keeping track of the body's
energy budget a healthy balance occurs
when we put in about as much energy as
we lose if we consistently put more
energy into our bodies than we burn the
excess will gradually be stored as fat
in our cells and we'll gain weight if we
burn off more energy than we replenish
we'll lose weight so we have to be able
to measure the energy we consume and use
and we do so with a unit called the
calorie one calorie the kind we measure
in food also called a large calorie is
defined as the amount of energy it would
take to raise the temperature of one
kilogram of water by one degree Celsius
everything we consume has a calorie
count a measure of how much energy the
items stores in its chemical bonds
the average pizza slice has 272 calories
there are about 78 in a piece of bread
and an apple has about 52 that energy is
released during digestion and stored in
other molecules that can be broken down
to provide energy when the body needs it
it's used in three ways
about 10% enables digestion about 20%
fuels physical activity and the biggest
chunk around 70 percent supports the
basic functions of our organs and
tissues
that third usage corresponds to your
basal metabolic rate a number of
calories you would need to survive if
you weren't eating or moving around add
in some physical activity and digestion
and you arrive at the official
guidelines for how many calories the
average person requires each day 2,000
for women and 2,500 for men those
estimates are based on factors like
average weight physical activity and
muscle mass so does that mean everyone
should shoot for around 2,000 calories
not necessarily if you're doing an
energy guzzling activity like cycling
the Tour de France your body could use
up to 9,000 calories per day
pregnancy requires slightly more
calories than usual and elderly people
typically have a slower metabolic rate
energy is burned more gradually so less
is needed here's something else you
should know before you start counting
calories the calorie counts on nutrition
labels measure how much energy the food
contains not how much energy you can
actually get out of it
fibrous foods like celery and
whole-wheat take more energy to digest
so you'd actually wind up with less
energy from a hundred calories serving
of celery than a hundred calories
serving of potato chips not to mention
the fact that some foods offer nutrients
like protein and vitamins while others
provide far less nutritional value
eating too many of those foods could
leave you overweight and mountain Irish
and even with the exact same food
different people might not get the same
number of calories variations in things
like enzyme levels gut bacteria and even
intestine length means that every
individual's ability to extract energy
from food is a little different so a
calorie is a useful energy measure but
to work out exactly how many of them
each of us requires we need to factor in
things like exercise food type and our
body's ability to process energy good
luck finding all of that on a nutrition
label
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