Chapter 10
Evaluation of the Overweight and Obese Patient
George A. Bray and Donna H. Ryan
Pennington Biomedical Research Center, Baton Rouge, LA 70808, USA
1. INTRODUCTION
The increases in rates of overweight and obesity in the United States, which have become apparent in the last 30 years [1], prompt concern among med- ical personnel because of the health risks associated with excess adiposity. Of particular concern among public health officials is obesity’s twin epidemic of type 2 diabetes [2]. However, the association of obesity as an independent risk factor for cardiovascular disease [3, 4] and as a contributor to risk for almost every type of cancer [5], are additional reasons for alarm. The societal and cul- tural values placed on slimness drive dieting patterns, even among those who are not at increased health risk for overweight. To help patients manage their health, physicians must be able to define the aspects of overweight that impose health risk. That indicates recognition of excess body fat, and in particular, excess central adiposity.
Overweight and obesity can be defined to inform health status from a pop-
ulation perspective and from an individual perspective. While the purpose of
this chapter is to guide treating physicians, and thus our focus is on the indi-
vidual, it is still informative to discuss overweight and obesity definitions from
a population level. The current definition for the US population is to catego-
rize overweight as body mass index (BMI) ≥ 25 to < 30 kg/m
2and obesity
as BMI ≥ 30 kg/m
2[6]. Such a definition allows us to track population trends
in overweight and obesity in the United States and around the world. Because
BMI tracks well with total body fat on a population level [7], such a definition
is acceptable from an epidemiologic standpoint. On an individual basis, these
definitions do not always serve to identify those at health risk because of excess
body fat. For those with increased muscle mass, such as body builders, BMI
overestimates health risks because the total body fat may not be increased, and
for the elderly, with a reduced lean mass, the BMI underestimates the health
risk of fatness. Thus, because of the implications for health risks and increased
demands on the health care system for advice and treatment, we need a set of
ground rules that define overweight and obesity in terms of health risk to the
individual and to guide a risk–benefit approach to selecting treatments. Health risks drive treatment options. Thus, information from waist circumference and the presence of comorbidities can be used in addition to BMI to determine an individual’s risk status.
2. DEFINITIONS
Obesity is an increase in body fat. In contrast, overweight is an increase in weight relative to some standard. Methods for determining body composition and the standards we use have improved over the past 25 years, greatly in- creasing the accuracy and ease of measuring body compartments in patients [8–11].
3. ANTHROPOMETRIC MEASURES
3.1. Height and Weight
Height and weight are best determined with a calibrated stadiometer and scales. It is best to standardize these procedures. In a research environment, these measures are made in a gown and without shoes according to a specific protocol. This approach can be adapted for the medical office, with attention to patient privacy, as is discussed later. In the office setting, it is only necessary to measure height once, but weight should be measured at each visit. These measures are used to determine BMI in kg/m
2. This index is in metric terms (weight in kilograms divided by the square of the height in meters), but it can also be calculated using pounds and inches if the appropriate correction factor is used. BMI = {weight (lbs)/[height (inches)]
2}× 703. Table 1 contains the BMI values for various heights and weights in lb/in and kg/m. In the office setting, BMI is determined from a chart like that in Table 1.
3.2. Waist Circumference
The circumference of the waist is the second essential anthropometric mea-
surement. There is no unified methodology for waist measurement. In a re-
search setting, a tape measure device with a fixed tension is used to eliminate
the effect of compression. One technique for positioning the tape measure is to
mark a point midway between the highest point of the iliac crest and the lowest
point of the costal margin in the mid-axillary line. The measure is then placed
horizontally on this mark and the measure taken in a relaxed patient during
expiration. In clinical practice, the most useful technique is to measure at the
top of the iliac crest. In clinical practice, the value of the waist measurement
is to identify persons with visceral adiposity. For BMI > 35 kg/m
2, the waist
circumference is going to be increased and there is little to be gained by its
Table 1. Body mass index using either pounds and inches or kilograms and centimeters
measurement. It is acceptable to omit waist measurement for class II obesity (BMI 35 to < 40) and class III obesity (BMI ≥ 40), in consideration of the sensitivity of the patient.
4. INSTRUMENTAL METHODS FOR MEASURING BODY FAT
The number and precision of methods for measuring body composition have
improved greatly over the past 25 years [9–12], but some of these methods are
expensive, limiting their usefulness in clinical practice (Table 2).
Table 2. Methods for measuring body composition
Ease of Can measure External
Cost use regional fat radiation
Anthropometric
Height and weight $ E No
Diameters $ E +
Circumferences $ E +
Skinfolds $ M +
Instrumental
Hydrodensitometry $$ E
aNo
Air displacement $$$$ D
aNo
(plethysmography)
Dual x-ray absorptio- $$$ M
a+ Trace
metry (DXA)
Isotope dilution $$ M
aNo
Impedance (BIA) $$ E
a+
Potassium counting $$$$ D
aNo
Conductivity (TOBEC) $$$ D
a±
Computed tomography $$$$ D
a++ Some
Magnetic resonance $$$$ D
a++
imaging
Neutron activation $$$$ D
aNo Larger
Ultrasound $$ M
a+
aSpecial equipment; E= easy; M = moderately difficult; D = difficult.
$= inexpensive; $$ = more expensive; $$$ = expensive; $$$$ = very expensive.
+ = good; ++ = very good; ± = possibly.
4.1. Dual X-ray Absorptiometry
Dual x-ray absorptiometry (DXA) instruments [9, 10] were developed to evaluate osteoporosis. DXA has replaced underwater weighing as the gold standard for determining body fat and lean body mass. In addition to accuracy, this method has the advantage of convenience and speed, as measurements can be done in about 10 minutes for individuals in a hospital gown.
4.2. Density
By weighing an individual in air and under water it is possible to divide the
body weight into fat and nonfat compartments, based on the fact that fat floats
and the nonfat components sink [13]. Underwater weighing is a good method,
but DXA is preferred, on the basis of both accuracy and convenience.
4.3. Isotope Dilution
Estimating body water by injecting a nonradioactive tracer of isotopic water (D
2O; H
218O;
3H
2O) makes it possible to calculate body fat and thus partition body weight into lean body mass and body fat. This method, density, and DXA have comparable accuracy [15]; however, the method is expensive and time consuming.
4.4. Bioelectric Impedance
Measurement of the impedance of the body to an alternating current pro- vides an easy and relatively inexpensive way to estimate body water [16].
However, most formulas for bioelectric impedance underestimate body fat in overweight patients [15], and, thus, bioelectric impedance analysis sacrifices accuracy to convenience.
5. IMAGING TECHNIQUES FOR BODY COMPOSITION
Regional body fat distribution can be reliably determined by either com- puted tomography (CT) or magnetic resonance imaging (MRI) [4, 5]. Because of their expense, these techniques should not be used for routine evaluation of visceral fat in the clinical setting. The waist circumference is the most useful clinical measure to assess visceral adiposity.
6. SUMMARY OF CLINICAL RECOMMENDATIONS FOR MEASUREMENT OF BODY COMPOSITION
Careful measurement of height, weight, and waist circumference are the essential measurements needed to begin evaluation of an overweight patient.
If the clinician is concerned that lean body mass is increased, and thus the contribution of body fat to an elevated BMI being difficult to assess, DXA (also density or isotope dilution) may be considered to more accurately assess total body fat. Although impedance measurements are used in many clinical settings, they often underestimate fat.
7. BODY FAT THROUGH THE LIFE SPAN
Several factors modify the percentage of body fat, including gender, age, level of physical activity, and hormonal status [17]. The percentage of body fat steadily increases with age in both men and women, as illustrated in Figure 1.
Women have a higher percentage of body fat than do men for a comparable
Figure 1. Changing body composition from gestation through adult life. There is a gradual in- crease in the proportion of body fat in adulthood. After puberty, females have greater proportion of body fat than do males. (From Friis-Hansen. In: Brozed J, ed, Human Body Composition.
Oxford: Pergamon Press, 1965;191–209.)
height and weight at all ages after puberty. Visceral fat in women is lower dur- ing the reproductive years, but rises rapidly to nearly male levels in the post- menopausal years, when risk for cardiovascular and other diseases increase sharply. Indeed, when differences in body fat distribution are considered, al- most all of the differences in excess mortality of men over women disappear, suggesting that the underlying factors leading to differences in fat distribution are significant in the risk of diabetes, heart disease, high blood pressure, and stroke in men.
8. PREVALENCE OF OVERWEIGHT
BMI is a useful measure for comparing populations; it allows us to divide a population into groups, compare these groups across national boundaries, and examine time trends.
Using measurements of a representative sample of the US population,
the percentage of overweight and obese Americans has been determined by
NHANES (National Health and Nutrition Examination Survey), beginning in
1960 [18] (Figure 2). The percentage of obese men and women defined as a
BMI ≥ 30 kg/m
2increased slowly in each of the first three surveys, but there
Figure 2. Prevalence of obesity (BMI ≥ 30 kg/m
2) in US adults as measured by NHANES sur- veys since 1963. There has been a dramatic increase in the prevalence of obesity, with doubling of rates in the last 25 years [18].
was a striking rise between 1980 and 1990. The increase in percentage of men with a BMI ≥ 30 kg/m
2nearly doubled, and the percentage of women with a BMI ≥ 30 kg/m
2rose by more than 50%. An even greater concern is the skewing of the population distribution. The problem is not just that the popula- tion distribution has shifted slightly to the right because of a small weight gain in the population. The problem is confounded by the rising prevalence of ex- treme obesity. The prevalence of class III obesity (BMI ≥ 40 kg/m
2) was 4.7%
of the adult US population in the 1999–2000 NHANES survey, increased from 2.9% in the 1988–1994 survey [1]. Minorities are at particular risk. A larger percentage of Hispanics and African Americans are overweight and obese than whites. Of particular concern is the 15.1% prevalence of class III obe- sity among African-American females in the 1999–2000 NHANES survey, which compares to 4.9% for non-Hispanic whites [1]. Over all, females are more likely to be obese than men [1].
The prevalence of overweight in children is also rising, according to surveys conducted over the past 30 years [19] (Figure 3). For children, overweight is defined as BMI > 95th percentile for height. From 1963 to 1970, six to 11- year-olds had a prevalence of 4.3% and in 12- to 17-year-olds, it was 4.6%.
From 1976 to 1980, according to the NHANES II survey, 7.5% of the six to
11-year-olds and the 12- to 17-year-olds were overweight. In the NHANES
III survey from 1988 to 1991, the prevalence in the younger children rose to
13.5% and to 11.5% in the 12- to 17-year-olds [19].
Figure 3. Prevalence of overweight in US children and adolescents as measured in NHANES surveys since 1963. There has been a dramatic increase, with tripling of rates for overweight in US children in the last 25 years [19].
9. CLINICAL EVALUATION OF OVERWEIGHT PATIENTS
Evaluation of health risks from weight status is the first step in formulating a treatment plan. Thus, both clinical and laboratory information are needed to evaluate overweight patients. Several reports provide guidance for this evalua- tion (NHLBI [6, 20]; AOA [21]; WHO [22]).
9.1. Body Mass Index
Overweight is usually assessed by measuring the BMI (see Table 1), and this step is the first in screening for obesity. BMI was originally proposed by Quetelet more than 150 years ago and correlates more closely with body fat content than do other anthropometric relationships of height and weight. Its advantages are ease of determination and the accuracy with which both height (stature) and weight can be measured. Its chief limitation is that, particularly in the normal BMI range (18.5 to 24.9 kg/m
2), the correlation with actual body fat content is sufficiently low that it is a poor guide to individual fat level. For BMI values above 25 kg/m
2and especially above 30 kg/m
2, it is a much better guide to the degrees of excess fat and risk to health.
Table 3 lists BMI ranges and the relative risk associated with each as modi-
fied by taking waist circumference into account. This table is derived from the
National Institutes of Health guidance on prevention and treatment of obesity
[6, 20]. As is discussed later, health risk may also be elevated for any given
BMI level, based on a history of comorbid condition, sedentary lifestyle, or of
history of weight gain, among other factors.
Table 3. Classification of overweight and obesity by BMI, waist circumference and associated disease risk
Disease risk
arelative to normal weight and waist circumference
Obesity Men ≤ 102 cm (≤ 40 in) > 102 cm (> 40 in) BMI (kg/m
2) class Women ≤ 88 cm (≤ 35 in) > 88 cm (> 35 in)
Underweight 18.5 – –
Normal
b18.5–24.9 – –
Overweight 25.0–29.9 Increased High
Obesity 30.0–34.9 I High Very high
35.0–39.9 II Very high Very high
Extreme obesity ≥ 40 III Extremely high Extremely high
aDisease risk for type 2 diabetes, hypertension, and CVD.
bIncreased waist circumference can also be a marker for increased risk even in persons of normal weight [6].
Figure 4. Relationship of BMI to risk for mortality in the US Physicians and Nurses Health Studies [23].
BMI shows a curvilinear relationship to risk for mortality [23], and although
many longitudinal population studies demonstrate this, we choose to illustrate
the relationship with data from the Nurses and Physicians Health Study cohorts
(Figure 4). Several points can be made from these data. They illustrate the
recently popular focus on the relatively small increase for mortality that is
evident in this population in the overweight category, BMI 25 < 30 kg/m
2.
They take a very large study, and long periods of follow-up, to demonstrate
the increased mortality risk for those in the overweight category, while the
increased risk for obese among American whites is readily demonstrated as
BMI exceeds 30. Other measures besides BMI, such as waist circumference and other risk factors, can serve to identify those with high risk in the BMI 25 to < 30 category. The cut points to define overweight and obese are derived from data collected on Caucasians. It is now clear that different ethnic groups have different percentages of body fat for the same BMI. For a given BMI, Asians tend to have more fat and African Americans the same or less fat. For the black American women in Figure 4, the risk for mortality with elevations in BMI is less prominent than for whites.
9.2. Waist Circumference
Estimation of body fat distribution can aid in assessing health risk. This is particularly true for those with BMI < 35 kg/m
2, and we do not endorse the routine ascertainment of waist circumference for BMI ≥ 35 kg/m
2, because the waist circumference is almost certainly elevated. Visceral fat and central fatness can be evaluated by several methods, but for practical purposes, the waist circumference is recommended. In the clinic, waist circumference can be measured with a flexible tape placed horizontally at the level of the nat- ural waistline or narrowest part of the torso as seen anteriorly [24]. Measuring the change in waist circumference is a good tool for following the progress of weight loss. It is particularly valuable when patients become more physi- cally active. Physical activity may slow loss of muscle mass, and thus slow weight loss while fat continues to be mobilized. Waist circumference can help in making this distinction. As with BMI, the relationship of central fat to risk factors for health varies among populations as well as within them. Japanese Americans and Indians from South Asia have relatively more visceral fat, and are thus at higher risk for a given BMI or total body fat than are Caucasians.
Even though the BMI may be below 25 kg/m
2, central fat may be increased and, thus, adjustment of BMI for central adiposity is important, particularly with BMI between 22 and 29 kg/m
2.
9.3. Weight Gain
Patients with a weight gain of more than 1 kg/year or more than 10 kg overall have an increased risk to health [25].
9.4. Sedentary Lifestyle
A sedentary lifestyle also increases the risk of early death. Individuals with
no regular physical activity are at higher risk than individuals with modest
levels of physical activity [26].
9.5. Laboratory and Other Measures
The relationship between obesity and increasing blood pressure is well known, and careful assessment of blood pressure should be part of the eval- uation. Laboratory measurements should include, as a minimum, lipids (total cholesterol, low-density lipoprotein [LDL] cholesterol, high-density lipopro- tein [HDL] cholesterol, and triglycerides), glucose, and uric acid. Sleep apnea and osteoarthritis should be assessed by a careful history.
10. THE METABOLIC SYNDROME
Identification of a constellation of risk factors that imposes higher risk for the development of type 2 diabetes and for cardiovascular disease is a key part of health risk appraisal in the office. In the United States, the National Choles- terol Education Program (NCEP) Adult Treatment Panel III has promoted a working diagnosis for metabolic syndrome that relies on the presence of three or more of the risk factors illustrated in Figure 5 [27]. The NCEP’s goal in promoting recognition of metabolic syndrome was to encourage physicians to prescribe lifestyle approaches as a way to prevent cardiovascular disease. The NCEP’s recommendation is that weight reduction, healthy diet, and physical activity be incorporated into the lifestyle of all individuals with the metabolic syndrome.
Recently, the International Diabetes Federation (IDF) has promoted another definition of metabolic syndrome [28] (Figure 6). The IDF definition relies on waist circumference as its central criteria and is easily applied in the clinical setting. The waist circumference cited by the IDF is lower than that used in the NCEP criteria, but the IDF states, “In the USA, the ATP III values (102 cm
Figure 5. Criteria for the metabolic syndrome, NCEO Adult Treatment Panel III, 2001, criteria.
At least three of the conditions must be met for the diagnosis of metabolic syndrome under this
classification [27].
Figure 6. Criteria for the metabolic syndrome, IDF criteria, 2005. To meet the criteria for metabolic syndrome in this classification, the waist circumference must be elevated and two other conditions must be met [28].
male; 88 cm female) are likely to continue to be used for clinical purposes.” It is the hope of the International Diabetes Federation that their consensus defi- nition of the metabolic syndrome will be adopted world-wide. The waist cir- cumference criteria are listed for Europid ethnic groups, but specific cutpoints are provided for other ethnicities.
11. ETIOLOGIC FACTORS UNDERLYING OBESITY
As part of the evaluation of overweight and obese patients in the clini- cal setting, etiologic factors causing obesity should be identified, if possible [29, 30].
• Genetic diseases and genetic predisposition. There are several extremely rare single-gene causes of obesity, but the usual genetic basis is to enhance susceptibility to environmental factors.
• Hypothalamic obesity. Hypothalamic obesity is rare in humans [31], but can be regularly produced in animals by injuring the ventromedial or paraven- tricular region of the hypothalamus or the amygdala. Hypothalamic obesity can follow surgical intervention in the hypothalamic-pituitary area or result from hypothalamic disease or trauma.
• Cushing’s syndrome. Obesity is one of the cardinal features of Cushing’s
syndrome, and the differential diagnosis of obesity from Cushing’s syn-
drome and pseudo-Cushing’s syndrome is clinically important for thera-
peutic decisions [32, 33]. If Cushing’s syndrome cannot be excluded, an
endocrine consultation would be appropriate.
Table 4. Drugs that produce weight gain and alternatives to their use
Drugs that cause Possible
Category weight gain alternatives
Neuroleptics Thioridazine; olanzaepine; Molindone; haloperidol;
quetiapine; riesperidone; ziprasiodone clozapine
Antidepressants
Tricyclics Amitriptyline; nortriptyline Protriptyline; bupropion;
Monoamine oxidase Imipramine mitrazapine nefazoadone inhibitors
Selective serotonin Paroxetine reuptake inhibitors
Anticonvulsants Valproate; carbamazepine; Fluoxetine, sertraline;
gabapentin topiramate; lamotrigine;
zonisamide Antidiabetic drugs Insulin; sulfonylureas; Acarbose; miglitol;
thiazolidinediones metformin; exenatide;
pramlintide; orlistat;
sibutramine
Antiserotonin Pizotifen
Antihistamines Cyproheptidine Inhalers; decongestants
-Adrenergic blockers Propranolol ACE inhibitors; calcium
-Adrenergic blockers Terazosin channel blockers
Steroid hormones Contraceptives; gluco- Barrier methods; non- corticoids; proges- steroidal antiinflam- tational steroids matory agents
Copyright 2001 George A. Bray.
