Handbook of Psychology

Epidemiology of Obesity 123

TABLE 6.2 World Health Organization Classification of Overweight
According to BMI and Risk of Comorbidities

Category BMI (kg/m^2 ) Disease Risk

Underweight 18.5 Low*
Normal weight 18.5...24.9 Average
Overweight 25.0
Pre-obese 25.0...29.9 Increased
Obese Class I 30.0...34.9 Moderate
Obese Class II 35.0...39.9 Severe
Obesity Class III 40.0 Very severe

*There is an increased risk of other clinical problems (e.g., anorexia
nervosa).

Measurement of Abdominal Fat

The health risks associated with obesity vary signi“cantly ac-
cording to the distribution of body fat (WHO, 1998). Upper
body (abdominal) fatness is more closely associated with ab-
normalities of blood pressure, glucose tolerance, and serum
cholesterol levels than is lower body obesity (Pouliot et al.,
1994). Consequently, individuals with abdominal obesity
incur increased risk for heart disease and for type 2 diabetes
mellitus. Because abdominal fatness can vary substantially
within a narrow range of BMI, it is important in clinical set-
tings to include a measure of abdominal obesity (James,
1996). For example, the waist-hip ratio (WHR) represents
one method of identifying individuals with potentially
health-compromising abdominal fat accumulation. A high
WHR (de“ned as 1.0 in men and .85 in women) re”ects
increased risk for obesity-related diseases (James, 1996).
Evidence, however, suggests that a simple measure of waist
circumference may provide a better indicator of abdominal
adiposity and the likelihood of detrimental health conse-
quences than does the WHR (James, 1996; Thomas, 1995). A
waist circumference measurement greater than 40 inches in
men and greater than 35 inches in women confers increased
risk for morbidity and mortality (James, 1996; NHLBI, 1998;
Pouliot et al., 1994).

EPIDEMIOLOGY OF OBESITY

Data from recent population surveys (Flegal et al., 1998;
Kuczmarski, Carrol, Flegal, & Troiano, 1997) indicate that
19.9% of the men and 24.9% of the women in the United
States are obese (i.e., BMI 30). An additional 39.4% of
men and 24.7% of women are overweight (i.e., BMI of 25.0
to 29.9). Collectively, the data show that the majority (54.9%)
of adults in the United States, approximately 97 million peo-
ple between the ages of 20 to 74, are overweight or obese.
The rates of obesity are highest among African American

women (37.4%) and Mexican American women (34.2%), and

additional percentages of each of these groups (29.1% and

33.4%, respectively) are overweight (Flegal et al., 1998).

Table 6.3 presents the current prevalence rates of overweight

and obesity by gender and by race/ethnicity.

Socioeconomic and age-related differences in obesity

rates are also evident in the population surveys. Women with

lower income or lower levels of education are more likely to

be obese than those of higher socioeconomic status, and obe-

sity rates generally increase with age across all groups. Cur-

rent rates of obesity by age group for men and women are

shown in Figure 6.1. Note that the obesity prevalence peaks

at ages 50 to 59 for both men and women.

Dating back to 1960, national surveys have assessed

height and weight in large representative samples of the

U.S. population. These data, from the National Health

Examination Survey (NHES; Kuczmarski, Flegal, Camp-

bell, & Johnson, 1994) and the National Health and

TABLE 6.3 Prevalence of Overweight and Obesity by Gender and

Race/Ethnicity

BMI (Weight Category)

25.0

25.0...29.9 30.0 (Overweight or

(Overweight) (Obese) Obese)

Gender, Race/Ethnicity % % %

Wo m e n

White 23.1 22.4 45.5

African American 29.1 37.4 66.5

Mexican American 33.4 34.2 67.6

All 24.7 24.9 49.6

Men

White 39.6 20.0 59.6

African American 36.2 21.3 57.5

Mexican American 44.0 23.1 67.1

All 39.4 19.9 59.3

Source:Data from NHANES III (Flegal et al., 1998).

20–29 30–39 40–49 50–59 60–69

Figure 6.1 Current prevalence of obesity (BMI 30) in United States.

Source:Data from NHANES III; Flegal et al., 1998.