The Dynamics of
Weight Control
Carolyn
Classick-Kohn,MS,RD
The Dynamics of
Weight Control-If you are over age 35, or you are short in
stature, or you’re a woman, it’s not your imagination that it is
harder for you to maintain a healthy body weight! Height,
sex, and your age play important roles in determining how many
calories you need to maintain your body weight. How many times
have you heard people say that they can’t eat the way they used
to? Or, “When I was 20, I never had to watch my weight.” Yet,
these same people at age 40, are fighting to lose 20 or 30
pounds. Let’s take a simple example of how calorie needs change
with age, and how it is so easy to gain weight in adulthood.
The Numbers Add Up
Example
1: A woman, age 20, 5’4” tall, 125 pounds, average physical
activity. Calorie needs: 1700/day
At age 30, this same woman would need 1650 Calories to maintain
her weight, and at age 40, she would need 1600 Calories to
maintain her weight of 125 pounds. So, over a 20 year period,
gradually, she needs about 100 fewer Calories each day to
maintain her weight. That’s a small difference over time, only a
change of about 5 Calories a day for each year after age 20.
That’s if her physical activity stays the same.
So, some people find a way to gradually adjust their calorie
needs with age so that they eat slightly less, or they increase
their physical activity to make up the difference, and their
weight stays the same.
For many people, though, gradual weight gain occurs instead. How
does this happen? Well, if the woman in this example failed to
modify her calorie intake, by the time she reached age 30, she
could have added an extra 10 pounds, and by age 40, perhaps
another 10 pounds, her weight creeping up with each year. This
is because metabolically, we slow down with each passing year of
adulthood, needing fewer calories to maintain our body
functions. It’s a small difference each day, perhaps the caloric
equivalent of a piece of hard candy, but it adds up slowly over
time.
In fact, about 70% of our calorie needs go to just maintaining
body functions. Only about 30% is needed for moving and extra
physical activity. But, that 30% makes a big difference - just
take a look at what happens when a person reduces their physical
activity and grows older! If the same woman at age 20
followed a program of some kind of regular physical activity
that burned about 150 extra Calories four times a week, then
stopped her exercise plan (injury, kids, change in routine) and
didn’t change her calorie intake, she could gain 9 pounds in
just one year! This is why injuries can lead to weight gain so
quickly - lots of sitting, and probably more eating, with no way
to compensate for it.
Well, enough about getting older! Gaining weight is not
inevitable with age, but if you add in reduced physical
activity, it’s easy to see how so many adults gain an extra 20
or 30 pounds, without really changing much in their intake of
food. Now, let’s look at height and sex, and how that affects
calorie needs.
Example
2: A woman, age 30, 150 pounds, 5’5”, average physical activity.
Calorie needs: 1824/day.
Now, a man, age 30, 150 pounds, 5’5”
tall, average physical activity. Calorie needs: 2040/day.
That’s
a difference in this case of 216 Calories per day, just for the
metabolic differences between men and women, regardless of age,
weight, or height! These calculations are pretty accurate, but
there are certainly individual differences. One of the reasons
that men get to eat more to maintain their weight is because the
normal body fat percentage for a man is about 12-20% of total
weight, while a normal body fat percentage for women is 20-30%
of total weight. So, for a man and woman who weigh the same, and
have a healthy body weight to begin with, the man will have a
greater percentage of his weight as lean tissue because his body
fat is lower. This lean tissue is what creates the need for more
calories.
While this seems a little unfair to women who are trying to lose
weight, this difference in calorie needs shows why a man can
lose weight a little more quickly than a woman. However, if the
woman who weighed 150 pounds in the example above was very lean
due to physical activity, you can bet that her calorie needs
would be much closer to the man’s. The take home point of this
is from a caloric point of view, it is very important for a
woman to burn calories through safe and moderate exercise, to
build lean tissue instead of just reducing calories. This, in
turn, allows you to maintain a healthy body weight and eat more
food at the same time. For men, it is equally important to
exercise to burn fat and to retain lean tissue when you follow a
“diet plan” to lose weight, so that you don’t lose the lean
tissue you already have!
Understanding that your age, sex, and height all play a role in
how many calories you need may help explain a few things, but
you can’t do anything about them. Genetically, we can only get
so tall, we can’t stop aging (yet), and not many people choose
to change their sex. But, you can do something about that 30% -
the percentage of calories attributed to moving around and
exercising. The more you move, the more you can affect your
calorie needs, so that you can enjoy a reasonable amount of food
without gaining weight. Moving around to burn an extra 100 or
150 Calories three or four times a week may seem small - the
equivalent of only about 2 slices of bread, or one beer, a few
cookies, but over time, it really makes the difference.
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