Page 175 - Nutrition Essentials for Nursing Practice

CHAPTER 7 Energy Balance 163

with excess weight (USPSTF, 2003). Although the USPSTF recently updated the 2003
statement on screening for obesity and overweight in adults, screening tests were not part
of its review (Moyer, 2012).

The formula to calculate BMI is weight in kilograms divided by height in meters squared
or weight in pounds divided by height in inches squared multiplied by 703. Nomograms
and tables that plot height and weight to determine BMI eliminate complicated mathemati-
cal calculations (Table 7.5).

Despite its widespread use as a screening tool, BMI is not without controversy. For
instance, the BMI levels that define overweight and obesity are somewhat arbitrary because
the relationship between increasing weight and risk of disease is continuous. Also, BMI
does not take body composition into account; a lean athlete may have well-developed mus-
cle mass and little fat tissue, yet if his BMI is high, he would fall under the designation of
overweight or obese. Conversely, an elderly person may have a normal BMI and be deemed
“healthy” despite a high amount of body fat masked by a low percentage of muscle mass.
Last, ethnic differences exist in the relationship between BMI and health risks. For instance,
because of genetic differences in body composition, the health risks of obesity occur at a
BMI lower than 30 for Asian Americans and higher than 30 for Black Americans.

Waist Circumference

Recent evidence indicates that waist circumference may be an acceptable alternative to
BMI measurement in some subpopulations (Moyer, 2012). In fact, the location of excess
body fat may be a more important and reliable indicator of disease risk than the degree of
total body fatness. Storing a disproportionate amount of total body fat in the abdomen
increases risks for type 2 diabetes and cardiovascular disease. Generally, men and postmeno-
pausal women tend to store excess fat in the upper body, particularly in the abdominal area,
whereas premenopausal women tend to store excess fat in the lower body, particularly in
the hips and thighs. Regardless of gender, people with a high distribution of abdominal fat
(i.e., “apples”) have a greater relative health risk than people with excess fat in the hips and
thighs (i.e., “pears”) (Fig. 7.2). The current waist circumference recognized as abdominal
obesity in the United States is 40 in or more for men and 35 in or more for women (Alberti
et al., 2009). As with BMI, ethnic groups differ in regard to where risk begins in relation
to waist circumference.

ENERGY BALANCE IN HEALTH PROMOTION

The state of energy balance is the relationship between the amount of calories consumed
and the amount of calories expended. As illustrated in Figure 7.3, when calorie intake and
output are approximately the same over time, body weight is stable. A “positive” energy
balance occurs when calorie intake exceeds calorie output, whether the imbalance is caused
by overeating, low activity, or both (Fig. 7.4). Over time, the calories consumed in excess of
need contribute to weight gain. Because a pound of body fat is equivalent to 3500 calories,
an “extra” 500 cal/day for a whole week can result in a 1-pound weight gain. Conversely,
a “negative” calorie balance occurs when calorie output exceeds intake, whether the imbal-
ance is from decreasing calorie intake, increasing PA, or (preferably) both (Fig. 7.5).

In 2009–2010, 68.8% of Americans 20 years of age and older were overweight or
obese, and 35.7% of American adults were obese (National Center for Health Statis-
tics, 2012). Excess weight, the outcome of a positive energy balance, also increases the
risk of cardiovascular disease, hypertension, type 2 diabetes, and certain cancers (U.S.