Although there is some overlap, treatments for dia-
betes depend on the type. Type 1
diabetes patients need
insulin. They must take multiple injections of insulin
daily, monitor their blood glucose often, watch their diet
(especially for foods high in sugar), and exercise. Patients
with type 2 diabetes must diet and exercise to control
their weight. Like type 1
patients, they must monitor their
blood sugar and watch their diet, being especially aware
of sugar content. Depending on severity, Type 2 diabetics
may also need supplemental injections of insulin to help
control their blood sugar.
The key to living with diabetes is control of blood glu-
cose. This can be accomplished through frequent moni-
toring of blood glucose levels, careful dietary planning,
exercise, and weight management. As noted earlier, many
diabetics may also need daily insulin injections. Let’s take
a closer look at this increasingly prevalent disorder.
Obesity Is an Imbalance Between
Energy Intake and Energy Expenditure
The percentage of overweight and obese Americans is
about 65%, an increase of 40% from the late 1970s. Obe-
sity is defined as body weight over 20% above an accepted
standard for height, age, sex, and weight, or a body mass
index (BMI) greater than 30 kg/m2
(Figure 14.16).
Obese patients are at increased risk for high blood pres-
sure, heart attack, stroke, pulmonary disease, diabetes
mellitus, arthritis, varicose veins, gallbladder disease, and
certain cancers (for example, breast, uterus, and colon
cancers).
Obesity is basically an imbalance between energy in-
take and energy expenditure. Energy intake includes both
eating and absorption of nutrients. Energy expenditure
includes three aspects: •
The rate of basal metabolism accounts for 65% of energy
expenditure. Basal metabolism is influenced by thyroid
hormones and results in production of the amount of
ATP necessary to keep you alive (that is, running your
heart, keeping you breathing, circulating your blood,
producing urine) when you are quietly resting.
Physical
activity
accounts
for
30-35%
of
energy
expenditure (lower in sedentary lifestyles)
The thermic effect of food,
the heat produced
while digesting a meal, accounts for 5-10% of energy
expenditure.
So if you increase your caloric intake but do not change
your energy expenditure (or, worse yet, reduce it), your
weight will increase. Conversely, if you reduce your food
intake and increase your energy expenditure (such as by
exercising), your weight will decrease.
From a physiological standpoint, scientists are just
beginning to unravel how body weight is regulated. Body
weight regulation includes a feedback system involving
sensors, an integrating system, and effectors:
Sensors.
Fat tissues and various organs of the GI tract
use nerves and hormones to send to the brain a
signal about the amount of fat tissue or the presence
or absence of food in the GI tract. These hormones
primarily include leptin, insulin, and ghrelin. Leptin
is a hormone secreted by fat tissue; the more fat, the
higher the leptin levels in the blood. Ghrelin is a
hormone secreted by the stomach just before a meal,
which stimulates food intake.
In te g ra tin g system .
The hypothalamus in the brain has
two neural circuits—one for stimulating appetite and
one for suppressing appetite. These circuits, which
read the chemical signals from fat tissue and the GI
tract, determine whether you need to eat.
E ffectors.
Effectors are neural and endocrine pathways
that respond to signals from the medulla to alter
feeding behavior and energy metabolism. For example,
the levels of thyroxin secreted by the thyroid gland
influence the rates of energy metabolism.
In the short term, this feedback system must operate to
control each individual meal. For example, your GI tract
must let your brain know when it is empty and that you
should start eating. Or it should let you know when it is
full and that you should stop eating. When your GI tract is
empty, parasympathetic nerves inhibit the satiety center
in the medulla, and ghrelin from the stomach signals the
hypothalamic appetite-stimulating center, thereby stimu-
lating you to eat. When the GI tract and stomach are full,
sympathetic nerves signal the satiety center to cause you
to stop eating; ghrelin levels also fall and no longer stimu-
late the hypothalamic appetite-stimulating center.
The feedback system also controls the body’s stores
of fat, thereby regulating body weight in the longer term.
The hormone leptin is the primary signal for the long-
term regulation of body fat, but ghrelin and insulin also
exert effects.
What causes obesity? While no single cause has been
identified, multiple factors contribute, including heredity,
eating habits, sedentary lifestyle, and social customs.
There are many approaches to the treatment of obesity,
targeting both energy inputs and energy expenditures:
424 CHAPTER 14
The Digestive System, Nutrition, and Metabolism
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