230
U N I T 2
Integrative Body Functions
Overweight and Obesity
Overweight and obesity have become global health prob-
lems, increasing the risk of hypertension, hyperlipidemia,
type 2 diabetes, coronary heart disease, and other health
problems. According to recent worldwide estimates,
1.7 billion people are classified as overweight, more than
1 billion have hypertension, and more than 500 million
have either diabetes or impaired glucose tolerance.
17
Obesity is defined as having excess body fat, enlarged
fat cells, and even an increased number of fat cells.
18
Clinically, obesity and overweight have been defined in
terms of the BMI. Historically, various world bodies have
used different BMI cutoff points to define obesity. In 1997,
the World Health Organization (WHO) defined the vari-
ous classifications of overweight (BMI
≥
25) and obesity
(BMI
≥
30). This classification was subsequently adopted
by the National Institutes of Health (NIH).
13
The use of
a BMI cutoff of 25 as a measure of overweight raised
some concern in that the BMI of some men might be
increased due to muscle rather than fat weight. However,
it has been shown that a BMI cutoff of 25 can sensitively
detect most overweight people and does not erroneously
detect overly lean people. An important caveat is that cer-
tain ethnicities (e.g., Asians), can develop complications
from lower levels of BMI and waist circumference than
Caucasians. This has resulted in ethnicity-specific defini-
tions being adopted (e.g., overweight in Asians is defined
as >23) by the WHO.
Obesity is associated with increased risk for develop-
ing many medical, psychosocial, and behavioral prob-
lems. In terms of health problems, many disorders occur
more frequently in obese people (Fig. 10-2). The most
important and common of these are hyperlipidemia,
hypertension, coronary artery disease, stroke, and type
2 diabetes mellitus. The increased weight associated
with obesity stresses the bones and joints, increasing the
likelihood of osteoarthritis. Certain cancers (endome-
trial, prostate, colon, uterine, ovarian), thromboembolic
disorders, and gastrointestinal tract disease (gastro-
esophageal reflux and gallbladder disease) are also more
prevalent in the obese.
19
Other conditions associatedwith
obesity include sleep apnea and pulmonary dysfunction,
menstrual irregularities and complications of pregnancy,
psychological distress, and nonalcoholic fatty liver dis-
ease (discussed in Chapter 30). Because some drugs are
lipophilic and exhibit increased distribution in fat tissue,
the administration of these drugs, including some anes-
thetic agents, can be more dangerous in obese persons. If
surgery is required, obese persons heal slower and are at
increased risk from anesthesia. Massive obesity, because
of its close association with so many health problems,
can be regarded as a disease in its own right. It is the
second leading cause of preventable death.
Causes of Overweight and Obesity
Factors that are thought to lead to the development of
overweight and obesity include the interaction of gen-
otype and environmental factors, including diet and
physical activity. Obesity is known to run in families,
suggesting a hereditary component. The question that
surrounds this observation is whether the disorder
arises because of genetic endowment or environmen-
tal influences. Studies of twin and adopted children
have provided evidence that heredity contributes to
the disorder.
20
The most recent update of the human
obesity gene map suggests that there are about 30 obe-
sity candidate genes that might contribute to the risk
of obesity in humans.
21
It is unknown what combina-
tions of genes and mutations are involved in these risk
factors and how environmental factors interact with
them.
Although genetic factors may explain some of the
individual variations in terms of excess weight, environ-
mental influences are major contributors. These influ-
ences include family eating patterns, inactivity because
of labor-saving devices and time spent on the computer
and watching television, reliance on the automobile for
transportation, easy access to food, energy density of
food, increased consumption of sugar-sweetened bev-
erages (especially fructose),
22
and increasing portion
sizes.
23
The obese may be greatly influenced by the avail-
ability of food, the flavor of food, time of day, and other
cues. The composition of the diet also may be a causal
Cerebral
atherosclerosis,
stroke
Sleep apnea
Fatty liver
Gallstones
Osteoarthritis
Polycystic ovaries
(younger women)
Diabetes
Risk of endometrial
cancer
Coronary artery
atherosclerosis,
myocardial infarction
Hypertension, left
ventricular hypertrophy
Hyperlipoproteinemia
FIGURE 10-2.
Clinical manifestations of obesity.
