The Distinction Between Body Weight, Body Fat, and Abdominal Fat in Occupational Standards

19 Pages·2010·0.3 MB·English

5264_e15_p732-749 9/29/04 12:59 PM Page 732
DIABETES TECHNOLOGY & THERAPEUTICS
Volume 6, Number 5, 2004
© Mary Ann Liebert, Inc.
Can You Be Large and Not Obese? The Distinction
Between Body Weight, Body Fat, and Abdominal Fat in
Occupational Standards
COL. KARL E. FRIEDL, Ph.D.
ABSTRACT
Weight control is an important early intervention in diabetes, but the nature of the associa-
tion between weight and disordered metabolism has been confused because fat mass and its dis-
tribution are only partly associated with increasing body size. Weight, fat, and regional fat place-
ment, specifically in the abdominal site, may each have distinctly different associations with
diabetes risk. Abdominal circumference may be the common marker of poor fitness habits and
of increased risk for metabolic diseases such as diabetes. This is an important question for pub-
lic health policy as well as for occupational standards such as those of the military, which are
intended to promote fitness for military missions and include strength and aerobic capacity, as
well as military appearance considerations. U.S. soldiers are heavier than ever before, reflecting
both increased muscle and fat components. They also have better health care than ever before
and are required to exercise regularly, and even the oldest soldiers are required to remain be-
low body fat limits that are more stringent than the current median values of the U.S. popula-
tion over age 40. The body fat standards assessed by circumference-based equations are 20–26%
and 30–36%, for various age groups of men and women, respectively, and the upper limits align
with threshold values of waist circumference recommended in national health goals. The basis
and effects of the Army standards are presented in this paper. U.S. Army body fat standards
may offer practical and reasonable health guidelines suitable for all active Americans that might
help stem the increasing prevalence of obesity that is predicted to increase the prevalence of
Type 2 diabetes.
INTRODUCTION kg/m2, and from this they speculated that the
Army was too fat to fight.1This writer took ad-
JUSTBEFOREthe United States invaded Iraq last vantage of a common mix-up between large
year, the Timesobserved that more than half and fat to spin a simple statistic into a perhaps
of U.S. soldiers were overweight by national predetermined conclusion about combat readi-
(cid:1)
health goals,i.e.,body mass index (BMI) of 25 ness. They were wrong about performance ca-
U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts.
The opinions and assertions in this paper are those of the author and do not necessarily reflect the official views
of the Department of the Army or the Department of Defense.
This work was presented in part at the Annual Meeting of the American Diabetes Association, in Orlando, Florida,
on June 6, 2004.
732
5264_e15_p732-749 9/29/04 12:59 PM Page 733
ARMY BODY FAT STANDARDS 733
pabilities; today’s Army is stronger and fitter body fat standards can reduce lifetime health
than ever before. Even the quality of recruits risks for soldiers remains to be discovered.
has not yet been compromised by the growing
epidemic of adolescent weight gain and seden-
OCCUPATIONAL STANDARDS FOR
tary habits.2 The truth is that soldiers who are
BODY COMPOSITION
large are ideal performers of many of the
Army’s common tasks, which depend largely
The dilemma of competing goals
on carrying and lifting strength.3 They are
larger than ever before, a desirable Army For the past 20 years (since 1984), the Army
trait—”large and in charge”—with appearance has strictly enforced body fat standards for sol-
of fitness and formidable size serving an im- diers. The purpose of these standards is to mo-
portant psychological advantage. Improved tivate good fitness and nutrition habits so that
nutrition and medical care has added an aver- soldiers are prepared to conduct their mission
age of 30 pounds of lean mass to the soldier, anywhere in the world on short notice. Obese
compared with Civil War soldiers over a cen- and poorly conditioned individuals are pre-
tury ago (Table 1).4,5 All of this revives a very dictably a hazard to themselves and their units
interesting question of what it means to health in a combat environment, and they are unlikely
and performance to be large but lean. Body to have time to become physically conditioned
weight surrogates of fatness such as BMI, long when they are called up for a military deploy-
used in epidemiology, are inadequate expres- ment. The stated primary objective of the Army
sions of obesity-related definitions today, but body fat standards is to ensure combat readi-
size undoubtedly has significance as well.5 ness, but this has multiple facets, some of
Even proper assessments of overall fatness or which may dictate different thresholds of ac-
“adiposity” may be far less important to health ceptable body fat or even conflict with each
outcomes than the distribution of the body fat other. Since many soldier job specialties require
to the abdomen.6,7 Waist circumference (WC) strength for tasks such as lifting and carrying,
is clearly emerging as an important marker of a big (and perhaps fat) individual may be a
chronic fitness and nutrition habits,8 a predic- good performer but does not necessarily have
tor of visceral fat,9and it may play a direct role the expected image of a ready and capable de-
in disease pathology.10WC is central to the cur- terrent force (trim military appearance), or sat-
rent Army standards that protect large but lean isfy health goals including reduced risk for
soldiers. Type 2 diabetes and other obesity-related dis-
This paper reviews the basis of the Army eases. The method of fat estimation could also
body fat standards, the method of body fat es- unintentionally thwart the intent of the stan-
timation that is a part of the standard, and some dards. For example, a typical male pattern of
of the apparent effects of these standards on upper body fat distribution, i.e.,a shift to more
soldier characteristics. Whether or not these abdominal and less gluteofemoral fat, in a
TABLE 1. AVERAGE BODY COMPOSITION ESTIMATES OF MALE SOLDIERS IN FIVE ERAS
Year
Variable 1864 1919 1946 1984 2000
Sample size 23,624 99,449 85,000 869 966
Age (years) 25.7 24.9 24.3 26.3 26.3
Height (in) 67.2 67.7 68.4 68.6 69.6
Body weight (lbs) 141 145 155 167 178
Abdominal circumference (in) 31.5 31.4 31.3 32.7 33.7
Body fat (%) 16.9 15.7 14.4 17.3 17.0
Fat-free mass (lbs) 117 122 133 138 148
Adapted from Friedl4with new data from Leu and Friedl.5
5264_e15_p732-749 9/29/04 12:59 PM Page 734
734 FRIEDL
woman may signify both greater strength ca- dergo periodic physical exams. This prelimi-
pacity as well as increased male-type health nary finding that Type 2 diabetes is not lower
risks.11–13 Too much emphasis on the WC for in the U.S. Army suggests other occupational
female soldiers might eliminate some of the risk factors (body size?), the occurrence in only
best performers in favor of a putative reduc- a discrete group of susceptible individuals, or
tion in health risk.14 Thus, body fat estimation failure to detect a health benefit that is more
methods are as much a part of the standard as noticeably accrued only later in life after re-
the percent body fat limits because every prac- tirement from the military.
tical method of assessment is based on a set of
assumptions that apply variably to individuals.
Ideally, a method will be selected that best cor- THE SHIFTING EMPHASIS IN MILITARY
responds to the intent of the standards. The WEIGHT STANDARDS
Army continuously reevaluates the standards
(and method) to fine-tune these standards on The U.S. Army has had weight standards in
the basis of any relevant new research. place for over a century, but the original em-
phasis on underweight has flipped to concern
about obesity.4 Originally, weight standards
Where is the Army’s health benefit?
were used to screen out recruits who were
Although health risk is only one of several chronically malnourished or had chronic ill-
reasons for the Army body fat standards, and nesses such as tuberculosis. The Army wanted
not even one of the most important ones to the large soldiers who might therefore be healthy,
Army mission of winning battles, disease risk strong, and looked like formidable opponents.4
provides the most definitive outcome in which Congress was prompted to start the School
to anchor fat standards. The current Army stan- Lunch program because so many potential re-
dards are specifically linked to thresholds of cruits were turned away for underweight in
health risk. The Army standards intentionally World War II. However, by the post-Vietnam
favor large but muscular soldiers, but it is cur- era, there was a perception that soldiers were
rently unknown if larger size, independent of becoming obese and had a poor level of fitness,
adiposity, increases the prevalence of certain calling into question both their deterrent value
health risks such as Type 2 diabetes compared (they didn’t lookfit to fight) and the level of mil-
with the general population, and if the body fat itary readiness (the capability to conduct the
standards provide an added health benefit. In- military mission). In 1976, this became a crisis,
cidence of Type 2 diabetes in the Army has reportedly precipitated after news services
been estimated at 1.7 cases per 1,000 person- panned their cameras across a line of ample bel-
years, based on data from the 1998 Defense lies in a military formation during a nationally
Medical Surveillance System, with an average televised military ceremony. This led to a new
age at diagnosis of 35 years, after 14 years of Army regulation with strict weight standards,
Army service.15 Very similar notes have been but the regulation included a significant loop-
reported for the U.S. population ages 20–44.15 hole that required a military physician to as-
This is surprising because of the factors that sess overweight soldiers to determine if they
would predict lower diabetes risk in soldiers. needed to lose weight or were just large. In
Health standards for entry into the Army are 1980, President Carter ordered a review of the
restrictive, excluding obese individuals. Sol- fitness of the military services. This resulted in
diers are tested for physical fitness on a semi- a Department of Defense Instruction that man-
annual basis, and this reinforces regular fitness dated new fitness and body composition stan-
habits; regular physical activity is measurably dards for all military services.16
higher in the Army than some of the other mil- It was innovative to replace unenforceable
itary services and the general American public. body weight standards and a subjective ap-
The existing body fat standards based on waist praisal of adiposity with circumference-based
girth are strictly enforced. Soldiers have access body fat estimations. These occupational stan-
to excellent health care and are required to un- dards remain unique to the U.S. military. After
5264_e15_p732-749 9/29/04 12:59 PM Page 735
ARMY BODY FAT STANDARDS 735
some adjustments based on new research, the logical changes with age, they were concerned
military Services have agreed to a single set of that average population values, rather than
equations for body fat assessment (Fig. 1),17–19 physiologically based values, might become ac-
but each of the four military services still set its cepted as normal.16
own body fat thresholds according to its mis-
sion requirements. The 1980 panel concluded
that the upper limits of body fat could be rea-
ARMY BODY FAT STANDARDS
sonably set at 20% and 30% for men and
women, respectively.16 However, the final in-
How the standards were set
struction to the services called for Department
of Defense-wide goals for body fat to be 20% The Army regulation uses weight screening
for all men and 26% for all women, apparently tables to identify soldiers who may be at risk
guided by the thinking that women were es- for exceeding the body fat standards. These are
sentially men with too much fat and that fe- based on BMI, and the most recent revision
male physical performance could be improved uses a range between 25 to 27.5 kg/m2. If a sol-
by simply legislating a lower body fat. Subse- dier exceeds his or her gender- and age-related
quent data from multiple studies and reviews, weight limits, he or she is measured for body
including the Defense Women’s Health Re- fat. If they also exceed their body fat limits
search Program, have corrected deficiencies in (Table 2), they are placed on the Army weight
Army health, fitness, and nutrition regulations control program and must successfully achieve
to account properly for the physiology of the their body fat standards or face dismissal for
female soldier rather than provide “accommo- failure to meet weight control standards. Army
dations” in existing male standards.20The 1980 weight tables for men are traceable to the 1912
panel also suggested older age standards at Medico-Actuarial tables, with male upper lim-
30% and 37% body fat for men and women, but its set at 125% of the desirable weight of young
with no data to guide standards for physio- men.4 This value of 27.5 kg/m2 proved to be
FIG. 1. Method of circumference-based body fat measurements. The equation for men is % body fat(cid:2)86.010(cid:3)
log (abdomen II circumference(cid:4)neck circumference)(cid:4)70.041(cid:3)log (height)(cid:5)36.76. The equation for women is
10 10
% body fat(cid:2)163.205(cid:3)log (abdomen I(cid:5)hip(cid:4)neck)(cid:4)97.684(cid:3)log (height)(cid:4)78.39.19Abdomen I is measured at
10 10
the thinnest part of the waist, Abdomen II is measured at the level of the navel. Both sites are measured with stom-
ach muscles relaxed.
5264_e15_p732-749 9/29/04 12:59 PM Page 736
736 FRIEDL
TABLE 2. ARMY WEIGHT CONTROL STANDARDS
Age categories (years)
17–20 21–27 28–39 40(cid:5)
Men
Screening table weights 25.9 26.5 27.2 27.5
% body fat limits 20 22 24 26
Women
Screening table weightsa 25.0 25.3 25.6 26.0
% body fat limits 30 32 34 36
aPending change from more stringent screening weights originally set with more stringent fat standards for female
soldiers.
very similar to the upper limit for men in 1988 ness level of 46 mL/kg/min in maximal aero-
national health guidelines (BMI 27.8 kg/m2, bic capacity.23Arbitrary increments in body fat
based on the 85th percentile of BMI for young and the screening table weights to predict over-
men and women in the U.S. population).21 fat were established between this upper and
Along with data on the average adiposity of lower bound to avoid an equally arbitrary and
older fit soldiers,22this formed the basis for the illogically large jump in allowable body fat at
upper limit of acceptable body fat in men, with one birthday. The tables and the standards for
an estimated equivalence of 26% body fat (Fig. women were then established in parallel to the
2). Department of Defense goals of 20% body male standards but have been adjusted several
fat for males were revalidated with the obser- times, along with an evolving appreciation for
vation that in a sample of soldiers, 20% body physiologically appropriate female standards.
fat corresponded to an acceptable average fit- Most recently, the female screening weights
FIG. 2. The basis of the Army body fat standards. Arbitrary age-related increments in allowable upper limits of
body fat are bracketed by upper limits of the body fat distribution around the average of fit young men and women
(15% and 25%, respectively) and by thresholds of increased health risk traceable to BMI and abdominal circumfer-
ence values (see text).
5264_e15_p732-749 9/29/04 12:59 PM Page 737
ARMY BODY FAT STANDARDS 737
have been raised to a minimum of BMI of 25 units. Nevertheless, the current limits hold up
kg/m2(Table 2), as women were attempting to well with new data. Gallagher et al.27 reported
meet more stringent weight tables to avoid be- that a BMI of 25–30 kg/m2 corresponded to
ing labeled as overweight even if they met the body fats of 20–24% in men and 32–36% in
fat standard; this was, in effect, holding female women, based on data from a large civilian
soldiers to healthier than “healthy” weights sample of various ages and ethnicities tested by
while also not identifying any additional dual energy x-ray absorptiometry (DXA) and
women exceeding the fat standard. Body fat using a four-compartment model. At the higher
standards based on a distribution above the av- end of BMI in an older population, the values
erage body fat of fit young men (15%) and also remain consistent. For example, in the
women (25%) have stood up well over time as Third National Health and Nutrition Examina-
reasonable and appropriate limits for fat gain tion Survey (NHANES III), where body fat was
before any physiological changes with aging estimated from bioelectrical impedance mea-
occur along with the accumulation of the ef- surements, average BMI of around 27.3 kg/m2
fects of career-long health and fitness habits and 26.6 kg/m2 for 40–49-year-old men and
(Fig. 2). women, respectively, corresponded to average
body fat of 24–26% (men), and 35–40%
(women).28 In a recent Army survey, men and
Equating BMI thresholds to percent body fat
women over age 40 averaged 26.9 kg/m2 and
The health-related upper limits of body fat 25.5 kg/m2, respectively, corresponding to mil-
for men (26%) and women (36%) have also itary WC-based body fat of 19.5% and 29.5%.5
withstood comparisons to new data on health These examples illustrate some of the varia-
risk thresholds, easily remaining within the rel- tions in population characteristics and methods
atively broad target range that results from the and still bracket a rough equivalence between
imprecision inherent in biological and mea- BMI-based health risk thresholds and the Army
surement variations. The best available meth- standards.
ods for body fat measurement typically vary by
0.5–1.0% in reproducibility and daily biologi-
Relating WC to percent body fat
cal variation, and 2.5–3.0% body fat in accuracy
against a criterion method.24 The actual signif- The relationship between military body fat
icance of any health risk threshold is not more and WC thresholds established in the NHLBI
precise than at least several percent body fat guidelines is easier to demonstrate, as the mil-
units because of the soft linkage to health out- itary’s method of body fat estimation is essen-
comes in different populations. There can also tially a calibrated WC. It should be cautioned
be large variation between population means that there are methodological differences be-
for different methods of body fat estimation; tween standards applied, with a wide range of
these are not readily interchangeable, and the measurements representing abdominal cir-
methods must be specified.25,26 On top of this cumferences that may fall anywhere from the
variation, trying to relate BMI-based health bottom of the rib cage to the top of the pelvis;
(cid:6)
guidelines [previous guidelines, BMI of 27.8 the military equations use the navel as the land-
kg/m2 for men and (cid:6)27.3 kg/m2 for women; mark for measurement in men and the thinnest
current National Heart Blood and Lung Insti- portion of the waist for women. Using average
tute (NHBLI) goals, BMI (cid:6)25 kg/m2] to per- values for height, neck circumference, and hip
cent body fat is a moving target that depends circumference (women only) of active duty sol-
on habits and traits that might influence the diers in the military equations, the male upper
balance of lean and fat in individuals in any limit of 26% body fat is predicted by a WC of
given population.21,27 Even within Army pop- 38.5(cid:7)(NHLBI guidelines: WC (cid:6)40(cid:7)); the female
(cid:7)
ulations, selective pressures and physical train- upper limit of 36% body fat is predicted by 35
(cid:6) (cid:7)
ing regimens vary the lean–fat relationship be- (NHLBI guidelines: WC 35 ). Sixty percent of
tween groups such as West Point cadets, new the male soldiers and 40% of female soldiers
Army recruits, and soldiers in various types of exceed a BMI of 25 kg/m2; very few soldiers
5264_e15_p732-749 9/29/04 12:59 PM Page 738
738 FRIEDL
below this BMI threshold exceed waist cir- behavior were still evident in Army regulations
(cid:7) (cid:7)
cumferences of 35 or 40 , and only 7% of all until just recently. With a skilled observer, vi-
female soldiers and 4% of all male soldiers ex- sual assessment of fatness can be as good as
ceeded these girths, compared with 12% of men many of the standard anthropometrically based
and at least 12% of women exceeding body fat assessments, but for general use the approach is
standards.5Thus, the Army WC-based body fat too variable and subjective.35Body size, as gen-
standards are more stringent than the health erally assessed using the standard Quetelet’s in-
threshold-based NHLBI guidelines, and very dex (BMI), has a good correlation with adipos-
few individuals exceeding the WC thresholds ity in population studies but is not useful in
are missed by the Army standards. assessing individuals, except for severe under-
weight where fat provides significantly less
variation in the assessment of minimum lean
BODY FAT MEASUREMENT
mass. Abdominal fat based on waist girth has
TECHNOLOGIES
long been recognized to be a good predictor of
(cid:7)
health risk, with a difference of more than 2 be-
Military body fat standards rely on predic-
tween waist and chest girths predicting in-
tive equations based primarily on WC (Fig. 1).
creased mortality, especially for diabetes, based
The method has been calibrated17,18 and vali-
on Metropolitan Life Insurance Company re-
dated19,29,30 against more accurate methods of
ports in the 1930s.36 In normal males, the pre-
total body fat measurement, including under-
dominant site of excess fat storage is in the ab-
water weighing (UWW), DXA, and multicom-
domen; for healthy young females, this is one of
partment models. However, it is important to
the last sites of fat deposition, following subcu-
note that the actual use of a more accurate to-
taneous locations ranging from thigh and hips
tal fat assessment would be less suitable to the
to upper arm, with differential regulation of
Army goals than this regional fat measurement
each depending on pregnancy, lactation, and en-
standard. This conclusion is predicated on the
docrine influences associated with other normal
view that adipose tissue does not behave as one
processes.9,37,38Thus, the military services were
homogeneous organ, but exhibits functional
able to quickly adopt circumference-based stan-
differences and is regulated differently be-
dards based on an earlier concept developed for
tween intraabdominal and various subcuta-
male Marines, but each of the four Services pro-
neous sites. A fair and appropriate application
duced different female equations,39which could
of these standards requires some assumptions
produce wildly varied body fat values for any
concerning the lability of fat at the measure-
one woman.40The original concept was that the
ment sites in response to changes in fitness and
characteristics (including ethnicity) of each Ser-
nutrition behaviors, as well as benefits of WC
vice differed and equations needed to be devel-
reduction to health outcomes. There are data to
oped that would be suitable to fat prediction for
support both assumptions.31–34
that Service; this was illogical since the goal was
to produce generalized equations that would
Practical methods of body fat estimation
apply fairly to all individuals. Only recently, the
Military researchers have considered many Department of Defense has settled on one best
approaches to assessing body type and body set of equations—those developed originally by
composition over time, and have been involved Hodgdon and co-workers for the Navy.17–19
in the development of many of these methods This followed 2 decades of studies on the best
(Table 3). Visual assessment is the age-old stan- method for the military services. In the 1980s the
dard used by commanders to choose soldiers, Army briefly used skinfold measurements and
but this reached a high state of refinement in the the equation of Durnin and Womersley41for the
now discredited eugenics movement with de- body fat standard because this had been well es-
tailed somatotyping of 100,000 soldiers at the tablished in Army research studies on physical
end of World War II to develop an occupational performance and environmental stressors.
classification scheme.4Remnants of this concept However, standardization of the technique was
of body type predicting human capabilities and too demanding and not practical for Army-wide
5264_e15_p732-749 9/29/04 12:59 PM Page 739
ARMY BODY FAT STANDARDS 739
TABLE 3. STANDARD PHYSICAL AND CHEMICAL METHODS OF TOTAL BODY FAT ASSESSMENT
Technology Measurement Theoretical premise Caveats and disadvantages
Human visual appraisal Visual inspection (% Practiced eye can detect Very imprecise
body fat) relative fatness (“fat quantification; errors
doesn’t flex”) at lower levels of fat
and when fat is well
distributed
Body mass index (BMI) Height and weight Increasing weight Large errors from
(kg/m2) corresponds to genetic, nutritional,
increasing proportion and physical training
of body fat variability
Skinfold thicknesses Sum of multiple Subcutaneous fat layer Technique difficult to
(SF) calipered skinfold represents total body standardize; varies
thicknesses (mm) fat with body fat
topography;
considers only
subcutaneous fat
Circumference-based Tape-measured girths at Combination of body Individual variations
equations (CIRCS) key sites (cm) girths can represent due to site-specific
total body fat emphasis
Underwater weighing Body density Constant FFM density Requires considerable
(UWW)a determined by water (g/cm3) (usually subject cooperation;
displacement 1.100 g/cm3 of FFM) large errors from
variations in lean
mass
Total body water Imbibed deuterium Constant FFM Specialized isotope
(TBW) dilution ((cid:1)g/mL) hydration (usually measurement
73% of FFM) required; large errors
from variations in
hydration
Total body potassium Natural K-40 gamma Constant FFM Specialized
(TBK) emission potassium (usually measurement device
2.66 g/kg) required
Bioelectrical impedance Body resistance to Resistance correlates Large errors from
analysis (BIA) electric current with FFM variations in
(ohms) hydration,
electrolytes, and body
dimensions
Dual energy x-ray Differential attenuation Constant attenuation Body thickness affects
absorptiometry of two x-ray energies coefficient of fat and measurements
(DXA) lean soft tissues
Multicompartment Combined Bone mass, density, and Reduced variability
models measurements, body water provide from multiple
usually DXA, UWW, key measures of body methods is offset by
TBW composition added measurement
errors
Neutron activation Induced gamma Constant relationship of Specialized and
analysis (NAA) emission from key elemental body expensive
elements composition measurement; higher
than minimal medical
risk
Methods are listed roughly in order of historical and technological origin. Imaging methods such as magnetic res-
onance imaging and computed tomography, currently used in regional assessments such as estimates of abdominal
fat volumes, still require further software development and validation for whole-body assessments. FFM, fat-free
mass.
aCan also be done using air displacement to estimate density similar to UWW.
use.42,43Bioelectrical impedance appeared to be assessments because of the wide excursions in
a sophisticated and accurate method that might values that could be produced by relatively
be able to replace the other methods being con- small changes in hydration status and other
sidered, but it proved unsuitable for individual factors.44,45
5264_e15_p732-749 9/29/04 12:59 PM Page 740
740 FRIEDL
Criterion methods of body fat estimation sessment as a by-product of the need to assess
and correct for soft tissue in the bone analysis.
The criterion method for all of the other meth- This body fat measurement is based on esti-
ods that were being tested in the 1980s was body mates only from the soft tissue pixels, thus os-
fat calculated from body density measured by tensibly eliminating the effects of variations in
UWW (or “hydrostatic” weighing). The criterion bone density. Percent body fat from DXA is also
methods of UWW and total body water mea- more reproducible than from UWW because it
surement, as well as their combination in “mul- does not require active participation of the sub-
ticompartment models” that considered direct ject.2UWW was a particular problem as the cri-
measurement of as many of the major compo- terion method for development of the Army
nents of body composition as possible, came out equations as half of the Army cannot swim and
of a landmark meeting at Natick Army labs in many study participants were not comfortable
1959.46This group recognized the deficiencies in performing maximum exhalations underwater.
single methods and proposed multicompart- The radiation exposure from DXA is low
ment models combining body water measure- enough that this method is commonly used for
ments and density. An Air Force body compo- repeated measures in longitudinal studies;
sition researcher, Thomas Allen, was one of the however, pregnancy testing of young women is
first to propose a four-compartment model that a common safety precaution. DXA provides a
included bone mineral,47but in the absence of a new criterion method for body fat estimation
practical method to measure whole body bone that is both more reproducible and accurate
mineral content, this had to be crudely derived than UWW, when more detailed multicom-
from anthropometry. This changed with the ad- partment model methods are not practical.
vent of DXA technology, which provides good
bone mineral content measurements for multi-
The future is in visceral adipose tissue (VAT),
compartment models. Multicompartment mod-
not fat
els improve the accuracy of body fat assess-
ments by including measures of several of the As the technology for body composition re-
body compartments that contribute the greatest search improves, the importance of regional fat
variability to the estimates. These usually in- placement to health consequences is becoming
volve body water (the largest component), bone better recognized, and the emphasis is moving
mineral content (the densest component), and to imaging techniques that assess VAT. Thus,
fat and the remaining lean mass components for the purpose of obesity-related health risk
based on body density. The largest error still predictions, BMI has been improved by total
comes from the UWW used to measure den- body fat measurement, followed by WC, now
sity.24 The current gold standard of body com- being replaced by VAT assessment. WC alone
position testing is in vivo neutron activation does not distinguish subcutaneous fat and
analysis, which involves irradiating individuals VAT, although the correlation between WC
with neutrons and measuring decay products of and visceral fat is stronger than that obtained
nitrogen, chloride, and calcium isotopes. The between BMI and visceral fat.50 A practical so-
four-compartment model approach compares lution based on correction with the addition of
well with this even more intensive elemental a suprailiac or abdominal skinfold measure-
multicompartment model of body composi- ment is problematic because with increasing
tion.48It is now possible to achieve a near-com- adiposity these skinfold sites quickly exceed
plete assessment of the composition of the liv- the span of standard spring-loaded calipers.
ing human body using combined chemical and More likely, future clinicians, epidemiologists,
elemental models, and this has been demon- and perhaps platoon sergeants will use a hand-
strated for six main chemical compartments (in- held device based on an imaging technology to
cluding cellular mineral content and glycogen) obtain a rapid and accurate assessment of VAT,
and 11 elements.49 and perhaps even the specific lipid composi-
DXA also provides a method of body fat as- tion.
5264_e15_p732-749 9/29/04 12:59 PM Page 741
ARMY BODY FAT STANDARDS 741
OCCUPATIONAL RELEVANCE OF BODY healthy individuals. There is a direct relation-
SIZE, BODY FAT, AND WC ship between lean mass and both strength and
work capacity, since strength is predicted by
Body size, body fat, and fat distribution each the cross-sectional area of muscle3and work ca-
have different significance in occupational pacity is determined in large part by the
standards. Acute outcomes affecting the ability amount of working muscle.51 These relation-
to perform the military mission today are the ships to the fat-free mass are gender neutral,
health and performance outcomes of greatest with data for male and female soldiers falling
importance to the Army, including strength, on the same regression line (Fig. 3). Because of
power, aerobic capacity, environmental injury human sexual dimorphism, women generally
risks, and acute health risks such as Type 2 di- have less fat-free mass and fall lower in the
abetes that potentially degrade soldier physi- physical strength and aerobic capacity range.
cal and mental performance. Thus, women would be most likely to be af-
fected by standards that set minimums of fat-
Physical performance
free mass (or minimum body mass index) to
BMI predicts lean mass at least as well as it ensure a minimum level of strength for safe
predicts fat mass, within the range of BMI of and effective lifting and carrying tasks. Current
FIG. 3. Relationships between physical performance measures (maximal lift strength and maximal aerobic capac-
ity) and percent body fat and fat-free mass (males, open circles and solid regression line; females, solid circles and
dashed regression line; fat-free mass relationships fit a single regression line regardless of gender). The key to soldier
physical capacity is body mass, or more specifically the fat-free mass component, not percent body fat. Data plotted
are from Fitzgerald et al.52