Calories stored =
calories eaten – calories burned.
Think of calories as money. If you earn (eat)
just a little more than you spend (burn), your savings (fat) will gradually grow
over time. When you eat fewer calories than you need for your daily activities,
your body dips into the savings and some of your fat is burned to supply the
needed energy. When this happens, you begin to lose weight. Even a small change
in your eating or exercise habits, if continued long enough, can make a big
difference in your weight over time.
Metabolism Made Easy
Your body burns calories through a process
called metabolism. Metabolism
supplies energy for physical activity, to digest food, to keep
your body warm, and
for organ function and repair. The number of calories your body
burns each day just for organ function and repair is called your resting
metabolic rate (RMR). Your RMR is often referred to in casual speech as
your resting metabolism or simply metabolism. This is the number of
calories your body would burn in a day if you did nothing but sleep. Your RMR
is mostly determined by how much muscle tissue you have, and how big your
organs (heart, liver, brain, etc.) are. The greater the mass of your muscles
and organs, the faster your RMR. Body fat also increases your RMR, but to a
lesser degree. Although there are various ways to calculate your RMR, the
following simple equation gives a good rough estimate:
RMR = fat-free weight x
10 + 500
For example, if you weigh
160 pounds, and 25 percent of that weight is from fat,
then your fat-free weight is 120 pounds. You would calculate
your RMR like this:
RMR = 120 x 10 + 500 = 1,700
calories
Thus, you would burn about 1,700 calories (about three
cheeseburgers) each day without even getting out of bed. If you weigh yourself
in kilograms instead of pounds, replace the 10 with 22 in the above
equations. To calculate your own RMR, you would, of course, need to know your percentage
of body fat. Skinfold measurements provide a reasonably accurate way of doing
this. The easiest way to take skinfold measurements is with body fat calipers,
which can be purchased online and usually come with detailed instructions for
calculating percentage of body fat.
My point here, however, is not to advocate
calorie counting as a tool for natural weight loss. It is to help you understand
the relationship between metabolism and weight loss. Your resting metabolism
mostly reflects the amount of organ and muscle tissue you have, and is about
the same as the metabolism of the next man or woman who has the same amount of
muscle and organ tissue. If that next man or woman seems to have an easier time
keeping the weight off than you do, a faster metabolism is probably not the
reason.
What Makes Your Metabolism Unique?
Women generally have slower RMRs than men,
mostly because of their typically smaller frames and less muscle mass. People
who are naturally larger framed and muscular have relatively fast RMRs. Thus,
the most important genes affecting your metabolism are the ones that influence
your frame size and muscle
mass. Having a slower RMR than someone else is not a problem
unless you try to eat as much as they do. Your body simply doesn’t need as many
calories to function. The RMR of a non-exercising adult typically decreases 2
to 5 percent every decade, mostly due to lack of physical activity and loss of
muscle and organ
mass. This trend is reversible. You can boost your metabolism at
any age with
muscle-building exercises. Losing weight can also decrease your RMR,
primarily because when you lose weight, you usually lose some muscle as well as
fat, and the lost muscle and fat are no longer using calories. Proper
musclebuilding
exercises during a period of gradual weight loss can help preserve
your muscle mass and keep your metabolism up.
_____________
You can boost your metabolism at any
age with muscle-building exercises.
_____________
Your daily activities also affect your metabolism.
In addition to the calories burned by resting metabolism, a nonexercising adult
will burn about 20 percent more calories each day moving around, digesting
food, and maintaining body temperature. A moderately active adult (for example,
one who plays an active sport or exercises three to five days a week) will burn
a total of about 50 percent more calories.
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