232
U N I T 2
Integrative Body Functions
The presence of excess fat in the abdomen out of pro-
portion to total body fat is an independent predictor of
risk factors and mortality. Both BMI and waist circum-
ference are positively correlated with total body adipose
tissue, but waist circumference is a better predictor of
abdominal or visceral fat content than BMI.
28
A waist
circumference of 88 cm (35 inches) or greater in women
and 102 cm (40 inches) or greater in men has been asso-
ciated with increased health risk
13
(see Table 10-2). In
general, men have more intra-abdominal fat and women
more subcutaneous fat. As men age, the proportion of
intra-abdominal fat to subcutaneous fat increases. After
menopause, women tend to acquire more intra-abdom-
inal fat. Increasing weight gain, alcohol, and low levels
of activity are associated with central obesity.
Although central obesity is usually considered to be
synonymous with visceral fat, CT or MRI scans can
differentiate central obesity into visceral fat and subcu-
taneous fat. Visceral fat stores are believed to be more
lipolytically active than subcutaneous fat and have a
greater potential to affect liver metabolism, given the fact
that the fatty acids in their venous drainage flow directly
to the liver. In addition to their lipolytic effects, visceral
adipocytes produce greater amounts of adipocytokines
(e.g., TNF-
α
, IL-6), except adiponectin whose levels are
decreased, resulting in a more insulin resistant, proin-
flammatory, and proatherosclerotic environment. These
changes contribute to the development of systemic insu-
lin resistance, hypertension, hyperlipidemia, and other
features of the metabolic syndrome, and are thought to
be associated with greater cardiometabolic risk.
15
Cardiometabolic risk represents the overall risk of
developing diabetes and/or atherosclerotic cardiovascu-
lar disease (e.g., myocardial infarction, stroke) due to a
cluster of modifiable risk factors. These include abdomi-
nal obesity, dyslipidemia (elevated levels of triglycerides
and low-density lipoproteins and decreased levels of
high-density lipoproteins), hypertension, insulin resis-
tance and elevated blood glucose levels, the presence of
inflammatory cytokines, and smoking. Emerging risk
factors include endothelial dysfunction and a prothrom-
botic state. Many of these risk factors are also key com-
ponents of what is termed the
metabolic syndrome
(see
Chapter 33).
15,16
Visceral obesity is also associated with
many other conditions including cancer (e.g., breast and
endometrial cancer), gallbladder disease, osteoarthritis,
menstrual irregularities, and infertility (especially as
part of the polycystic ovarian syndrome) (see Fig. 10-2).
Weight loss causes a preferential loss of visceral fat (due
to higher turnover of visceral fat cells than subcutaneous)
and can result in improvements inmetabolic and hormonal
abnormalities. Although peripheral obesity is associated
with varicose veins in the legs and mechanical problems,
it is not as strongly associated with cardiometabolic risk.
Prevention andTreatment of Obesity
Emphasis is being placed on the prevention of obesity.
It has been theorized that obesity is preventable because
the effect of hereditary factors is no more than moderate.
A more active lifestyle together with a low-fat diet
(<30% of calories) is seen as the strategy for prevention.
The target audience should be children, adolescents, and
young adults.
29
Tools needed to achieve this goal include
promotion of regular meals, increased intake of fruits
and vegetables, substituting water for calorie-containing
beverages, decreased television viewing time, a low-fat
diet, and increased activity.
30
Other experts target the
high-risk period from 25 to 35 years, menopause, and
the year after successful weight loss.
The current recommendation is that treatment is
indicated in all individuals who have a BMI of 30 or
higher or who have a BMI of 25 to 29.9 or a high
waist circumference plus two or more risk factors.
31
Treatment should focus on individualized lifestyle mod-
ification through a combination of a reduced-calorie
diet, increased physical activity, and behavior therapy.
Before treatment begins, an assessment should be made
of the degree of overweight, the person’s eating habits,
the person’s physical activity level, and the presence of
obesity-associated risk factors and complications.
31
It
also is advisable to determine the person’s barriers and
readiness to lose weight.
Dietary therapy should be individually prescribed
based on the person’s overweight status and risk pro-
file.
30
The diet should be a personalized plan with real-
istic goals that are 500 to 1000 kcal/day less than the
current intake. The aim should be for weight loss ini-
tially, followed by a strategy for weight maintenance.
Many popular diets exist such as Atkins, Ornish, Weight
Watchers, and South Beach. A recent study comparing
several of these diets suggested that adherence to the diet,
not the diet itself, is most closely associated with weight
loss (i.e., the best diet is the one the person likes best).
32
There is convincing evidence that increased physical
activity decreases the risk of overweight and obesity.
In addition, it reduces cardiovascular and diabetes risk
beyond that achieved by weight loss alone. Although
physical activity is an important part of weight loss
therapy and helps with maintaining weight loss, it does
not independently lead to a significant weight loss.
33
It may, however, help reduce abdominal fat, increase
cardiorespiratory fitness, and prevent the decrease in
muscle mass that often occurs with weight loss. Exercise
should be started slowly with the duration and intensity
increased independent of each other.
Techniques for changing behavior include self-monitoring of eating habits and physical activity, stress
management, stimulus control, problem solving, contin-
gency management, cognitive restructuring, social sup-
port, and relapse prevention.
30
Pharmacotherapy and
surgery are available as adjuncts to lifestyle changes in
individuals who meet specific criteria. Pharmacotherapy
is usually considered only after combined diet, exercise,
and behavioral therapy have been in effect for a reason-
able period of time. Weight loss surgery is usually lim-
ited to persons with a BMI greater than 40, those with
a BMI greater than 35 who have comorbid conditions
and in whom efforts at medical therapy have failed,
and those who have complications of extreme obesity.
However, more recent studies have shown the potential
