DiGestioN aND NUtritioN 217hoW can you maintain a healthy body Weight?- To maintain an acceptable body weight, caloric intake must be
in balance with energy used in basic metabolism and physical
activity. - Basal metabolic rate, physical activity, age, hormones, and
emotions all influence the body’s energy use.
taKe-Home messageappetite The desire to eat,
apart from the physical need
for food.
BMR Basal metabolic
rate, the amount of energy
needed to sustain body
functions.
kilocalories The standard
measure of food energy.
One kcal equals 1,000 calo-
ries of heat energy.(HDL) and the capacity of body cells to respond to insu-
lin, the hormone that promotes the uptake of blood sugar.
A build-up of excess fat triggers genetic changes that
result in inflammation. This fat-related inflammation
may be a factor in the strong correlation between obesity
and heart disease.
BMI is only a general standard for determining weight
status. Why? One reason is that muscle weighs more than
fat, and BMI doesn’t factor in the ratio of muscle to fat in an
individual’s body. The ratio is higher in males, whose bod-
ies tend to be more muscular, and it also varies depending
on a person’s race, age, and general fitness. For instance,
a trained athlete’s well-developed muscles may push him
or her beyond the “healthy weight” BMI category even
though the person is not overfat and in fact is in good
physical condition. Taking into account the correlation
between mid-body fat stores and obesity, many authorities
believe that the best overall indicator of “weight fitness”
is a combination of BMI and a measurement of an indi-
vidual’s waist circumference.
When someone is overweight, the usual culprit is an
unbalanced “energy equation” in which too many food
calories are taken in while too few calories are burned. We
measure food energy in kilocalories (kcal). A kilocalorie
is 1,000 calories of heat energy. (Calorie, with a capital C,
is shorthand for a kilocalorie.) A value called basal
metabolic rate (BMR) measures the amount of energy
needed to sustain basic body functions. As a general rule,
the younger you are, the higher your BMR. But like BMI,
BMR also varies from person to person, and it is influenced
by the amount of muscle tissue in the body, emotions, hor-
mones, and differences in physical activity. Adding BMR
to the kcal needed for other demands (such as body move-
ments) gives the total amount of food energy you need to
fuel your daily life.
To figure out how many kcal you should take in daily
to maintain a desired weight, multiply that weight (in
pounds) by 10 if you are sedentary, by 15 if you are fairly
active, and by 20 if highly active. From the value you get
this way, subtract the following amount:
Age 20–34 Subtract 0
35–44 100
45–54 200
55–64 300
Over 65 400
For instance, if you want to weigh 120 pounds and are very
active, 120 3 20 5 2,400 kilocalories. If you are 35 years
old and moderately active, then you should take in a total
of 1,800 2 100, or 1,700 kcal a day. Along with this rough
estimate, factors such as height and gender also must be
considered. Because males tend to have more muscle, they
tend to burn more calories (they have a higher BMR); hence
an active woman needs fewer kilocalories than an active
man of the same height and weight. Nor does she need as
many as another active woman who weighs the same but
is several inches taller.
genes, hormones, and activity affect weight
Scientists have identified several genes that code for
hormones that influence appetite. One of them, ghrelin
(grell-in), is made in the stomach.
It stimulates appetite. When your
stomach is empty, more ghrelin is
released. The level goes down again
after a meal.
The fat-filled cells in adipose tis-
sue produce a different hormone,
leptin, which acts on certain cells
in the brain. Leptin suppresses
appetite and so may help prevent
overeating. A few researchers have
speculated that some people with
weight problems have developed “leptin resistance,” in
which the hormone does not have its usual appetite-
suppressing effects in the brain.
For most people, maintaining a healthy weight over
the years requires balancing their “energy budget” so that
energy in—calories in food—equals energy used by body
cells. Losing a pound of fat requires expending about
3,500 kcal. Weight-loss diets may produce this deficit tem-
porarily, but over the long haul keeping off excess weight
means pairing a moderate reduction in caloric intake with
an increase in physical activity (Table 11.7). Exercise also
increases the mass of skeletal muscles, and even at rest
muscle burns more calories than other types of tissues.activityenergy expended
(calories per kilogram of
body weight per hour )
Sitting quietly 1
Standing 2
Walking slowly 3
Bicycling to class 4–7
Swimming 6–10
Basketball game 8
Running (5 mph) 8Table 11.7 Energy Expended in Some Common Activities© Yuri Arcurs/Shutterstock.com© Flashon Studio/
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