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| Journal of the New Zealand Medical Association,
17-December-2004, Vol 117 No 1207
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Body size, body composition, and fat distribution: a
comparison of young New Zealand men of European, Pacific Island, and Asian
Indian ethnicities
Elaine Rush, Lindsay Plank, Vishnu Chandu, Manaia Laulu,
David Simmons, Boyd Swinburn, Chittaranjan Yajnik
It is widely recognised that obesity (defined as an excess
of body fat) and obesity-related diseases are an increasing global problem now
reaching epidemic proportions.1 Because of its
general use and ease of measurement, body mass index (BMI) is commonly used as a
surrogate measure for obesity. The World Health Organization (WHO) cut-off point
for classification of obesity as a body mass index (BMI) above 30
kg/m2 is intended as an internationally useful
threshold for reflecting risk for Type 2 diabetes and cardiovascular diseases.
Based on this cut-off, Asian immigrants from the Indian
subcontinent have low rates of obesity yet, relative to Europeans, they have a
higher prevalence of coronary heart disease and Type 2
diabetes.2–5
Increased BMI levels explain only about half of the
increased prevalence of diabetes6 and
hypertension7 among Pacific Island peoples
compared with New Zealand Europeans. In New Zealand (specifically, in inner
urban South Auckland), the prevalence of Type 2 diabetes in Asian Indian peoples
is more than four-fold and in Pacific Island peoples more than two-fold higher
than in Europeans.8 These observations are of
particular concern because of the increasing size of the resident Asian Indian
and Pacific Island populations in this country. The 2001 census indicated that
there are now more people of Asian than Pacific Island ethnicity resident in NZ.
The Asian Indian subgroup comprises approximately 26% of the New Zealand
Asian population.9
Ethnic differences in body build, fat patterning, and
muscularisation may all contribute to differences in the relationship between
BMI and body fat between ethnic groups. Asian Indians have a more central
distribution of body fat than Europeans,2 which
is associated with increased risk of diabetes Type 2 and ischaemic heart
disease.10,11 Polynesians have higher bone mass
and muscle mass than Europeans.12–14
The WHO has recognised the deficiencies of a universal
cut-off for overweight and obesity15,16 and in
a recently published report17 suggested that
further body composition studies of Asian and Pacific Island populations are
needed to determine equivalent fatness levels and the relation of BMI to body
size.
Dual-energy X-ray absorptiometry (DXA) is widely accepted as
a valuable technique for the assessment of body composition and, in particular,
fat distribution, muscle mass and bone mass. While not without drawbacks as a
reference method,18 it has clear advantages
over the traditional anthropometric approaches such as skinfold thicknesses,
girths, and BMI. A significant drawback is that individuals with very high BMI
are not easily accommodated.
On the other hand, the technology provides a more direct
assessment of total body fat than anthropometric methods and offers regional
composition analysis. We are not aware of any comparative analysis of the body
composition of European, Asian Indian, and Pacific Island subjects using this
technique.
We sought in the current study of a group of young healthy
males who underwent DXA to identify ethnic differences in:
MethodsData from healthy male
volunteers aged 17–30 years, who participated in cross-sectional studies
of body composition conducted in the Department of Surgery, University of
Auckland, were examined. All studies were approved by the local ethics
committees and all participants provided written informed consent. Recruitment
for these studies, principally from the urban Auckland area, was by personal
contact, advertisement, or through existing networks of the recruiters.
Exclusion criteria were: total joint replacement,
lifting weights more than once per week, major medical conditions (such as
diabetes or cancer), and medication which could possibly affect body composition
(such as oral steroids). Only one member of a family was measured. In addition,
one subject was subsequently excluded from analysis because of a large
difference (>3 kg) between recorded scale weight and DXA weight (sum of fat
mass, fat-free soft tissue and bone mineral content). Of 114 volunteers, 64
self-identified as European, 31 as Pacific Island, and 19 as Asian
Indian.
Height and weight were measured with participants
wearing light clothing or standard hospital gown and no shoes. An estimated
clothing weight was subtracted. Body composition (fat, fat-free soft tissue, and
bone mineral content) and whole-body bone mineral density measurements were made
using a single DXA machine (model DPX+ with software version 3.6y, Lunar
Radiation Corp., Madison, WI). Fat-free mass (FFM) was calculated as the sum of
the values for fat-free soft tissue and bone mineral content. Percent body fat
was calculated as 100 x fat mass/(fat mass+FFM).
For assessing regional fat distribution, the whole-body
DXA scans were analysed. Abdominal and thigh regions of interest were defined by
the criteria of Ley et al.19 Abdominal fat was
obtained from analysis of a region of interest positioned with the lower
horizontal border on top of the iliac crest and the upper border approximately
parallel with the junction of the T12 and L1 vertebrae. The sides of this region
were adjusted to include the maximum amount of abdominal tissue. A region of
interest of identical height placed over the thighs (with the upper horizontal
border positioned immediately below the ischial tuberosities) was used to obtain
fat content of the thighs. The lateral margins were adjusted to follow the shape
of the thighs.
Appendicular skeletal muscle mass (ASMM) was derived
from the DXA scans as total limb mass minus the sum of limb fat mass and wet
bone mass, estimated as bone mineral content divided by
0.55.20 In this model, mass of the skin and
associated dermal tissues is assumed to be negligible relative to the skeletal
muscle component.
Results are presented as means ± SD. Between-group
differences in subject characteristics were tested using one-way ANOVA followed
by pairwise comparisons if a significant F test was obtained. Analysis of
covariance was used to adjust body composition results for comparison across
ethnic groups. Before carrying out analysis of covariance, similarity of
regression slopes among the ethnic groups was verified by examining the
significance of the interaction between the covariate(s) and the group variable.
Data were analysed using SAS software, version 6.12 (SAS Institute Inc., Cary,
NC). Results with p values <0.05 were considered significant.
ResultsThe subject characteristics are
summarised in Table 1. Pacific Island men in this study were heavier with higher
BMI than Europeans and Asian Indians. Asian Indians were shorter than Pacific
Islanders and significantly fatter than Europeans and Pacific
Islanders.
As a proportion of total body fat, abdominal fat was
significantly higher for Asian Indians than Europeans (p<0.0001) or Pacific
Islanders (p<0.0001), while thigh fat was significantly lower than Europeans
(p=0.037) or Pacific Islanders (p=0.015) (Table 1). After adjustment for weight,
height, and %BF, the ratio of abdominal to thigh fat was significantly higher
for Asian Indians than Europeans (p=0.022) and Pacific Islanders
(p=0.002).
ASMM for Pacific Islanders was significantly higher than
Europeans (p<0.0001); and for Europeans, ASMM was significantly higher than
Asian Indians (p=0.0021) (Table 1). This pattern remained after adjustment of
ASMM for height and weight, with Pacific Islanders having significantly higher
ASMM than Europeans (p<0.0001), and Europeans having significantly higher
ASMM than Asian Indians (p=0.0012).
After adjustment for height and weight, bone mineral density
was significantly higher in Pacific Islanders than European (p=0.0009) and Asian
Indian (p=0.0014). Adjusted bone mineral density for European was similar to
that for Asian Indian (p=0.46). When adjusted for height and weight bone mineral
content was significantly higher in Pacific Islanders than European (p=0.0021)
and higher in European than Asian Indian (p=0.0008).
Table 1. Characteristics of 64 New Zealand European, 31
Pacific Island, and 19 Asian Indian men aged 17–30 years
ASMM=appendicular skeletal
muscle mass; *analysis of variance; Ep<0.05
vs European, Pp<0.05 vs Pacific
Island
Curvilinear relationships between %BF and BMI for each
ethnic group were linearised by logarithmically transforming BMI (Figure 1). No
significant difference was found between the slopes of the regressions of %BF on
the logarithm of BMI for the three ethnic groups, but covariance analysis showed
their elevations to be significantly different (p<0.0001).
The common slope regression equation for predicting %BF from
BMI for the three ethnic groups was:
where group1 is coded as 0 for European, 1
for Pacific Islanders, 0 for Asian Indians—and group2 is coded as 0, 0, 1
for these respective ethnic groups. Hence, for fixed BMI, compared with
Europeans, Pacific Islanders had lower %BF by 3.8% (95% confidence interval:
1.4%–6.1%) and Asian Indians had higher %BF by 7.6% (5.0%–10.2%). At
a BMI of 30 for Europeans the predicted %BF (28%) equates to a BMI of 33 for the
Pacific Islanders and 25 for the Asian Indians (Table 2).
Table 2. Comparison of European body mass index (BMI)
and corresponding percent body fat with estimated BMI equivalents for Pacific
and Asian Indians derived from equations relating BMI to percent body
fat
Figure 1. Relation between percentage body fat (%BF)
and BMI for 64 European (closed circles), 31 Pacific Island (open circles), and
19 Asian Indian (triangles) men. The common slope linear regressions are given
by %BF = 105.8 log10(BMI) – intercept,
where intercept=128.4 for the European (solid line), 132.2 for the Pacific
Island (dashed line), and 120.8 for the Asian Indian men (dotted line)
DiscussionIn a group of young European,
Pacific Island and Asian Indian young men, we have shown that the relationship
between percent body fat and BMI is ethnicity specific.
The most commonly used measure of obesity is BMI, and we
found that, for a fixed BMI, Pacific Island men had significantly less body fat
while Asian Indian men had significantly more body fat than their European
counterparts. At a fixed %BF, BMI in Pacific Island men was 2–3 units
higher and in Asian Indian men was 3–6 units lower than in European men.
The BMI differences are smallest at low %BF and diverge with increasing %BF.
This effect is seen in Table 2 and also is evident in Figure 1 when allowance is
made for the logarithmic transformation of BMI. The results for Pacific Island
men confirm our previous
observations.21
Ethnic differences in the BMI-body fat relationships may be
explained, at least in part, by differences in body build, particularly
muscularity. We have shown that, compared with European men of similar weight
and height, Asian Indian men have significantly less skeletal muscle in the
limbs while Pacific Island men have significantly more. (Appendicular skeletal
muscle is approximately 75% of total body skeletal muscle
mass.)22
We have also shown, by examination of the distribution of
fat in our subjects, that Asian Indian men have a more central fat deposition
pattern than European or Pacific Island men. The propensity for abdominal
adiposity found in Asian Indians had been inferred from measurements of
waist-to-hip girth ratios in a number of
studies.2,23 Central obesity is closely
associated with risk for cardiovascular disease and Type 2
diabetes.3
The greater bone mineral mass and bone density that we
observed in Pacific Island men (relative to Europeans) may also contribute to
differences in the body fat-BMI relationship for these ethnic groups. While bone
mineral mass was lower in Asian Indians than Europeans, their bone mineral
density was similar after adjustment for body size. Others have shown that both
bone mineral density and bone mineral content in Asian men (predominantly
Chinese) were similar to European men after controlling for weight, height, and
age.24 Age was not a significant covariate for
our restricted-age range data.
A limitation of the present study is the comparatively small
Asian Indian group and our results need to be confirmed with a larger sample
from this ethnic group. In addition, our study does not address the other Asian
subgroups which make up the majority of Asians in New Zealand.
The WHO BMI classifications of overweight (≥25
kg/m2) and obesity (≥30
kg/m2), although intended for international
use, are based on the relationship between BMI and cardiovascular morbidity in
Western populations.1 Based on percent body fat
levels a BMI of 26 kg/m2 has been suggested as
an obesity cut-off point in Asian Indians equivalent to that for
Europeans,25 and revised cut-off values to
define overweight (23 kg/m2) and obesity (25
kg/m2) in Asian Indians have been proposed by
the WHO.15
Current New Zealand Ministry of Health cut-offs for
‘overweight’ and ‘obesity’ are 26 and 32
kg/m2, respectively in both Maori and Pacific
Island adults. Studies are required to define the BMI range that may be
considered ‘healthy’ in Asian Indian and Pacific Island people on
the basis of risk for obesity-related diseases. A consistent finding among
migrant Asian Indian populations is hyperinsulinaemia and insulin
resistance,26 characteristics which may be
important in the development of type 2 diabetes and cardiovascular disease.
Simmons et al27 have
reported that young Asian Indians are relatively hyperinsulinaemic compared to
their European counterparts with the same BMI. Vikram et
al28 have shown that Asian Indians with
‘normal’ BMI (<25 kg/m2) have
high cardiovascular disease risk. Pacific Islanders in New Zealand, by contrast,
are not hyperinsulinaemic relative to Europeans of the same BMI
29 and whilst they have a high prevalence of
type 2 diabetes, they are believed to have a lower rate of cardiovascular
disease.30
Our results demonstrate the marked differences in body
build, body composition, and fat distribution that characterise male New
Zealanders of European, Asian Indian and Pacific Island ancestry. We speculate
that these may be related to differences in risk for cardiovascular disease and
different pathways to Type 2 diabetes among these ethnic groups. The results
emphasise the inadequacy of universal BMI cut-off points for determination of
percentage body fat and obesity and the need to consider ethnic-specific weight
targets.
Author information:
Elaine Rush, Associate Professor, Faculty of Health,
Auckland University of Technology, Auckland; Lindsay Plank, Senior Research
Fellow, Department of Surgery, University of Auckland, Auckland; Vishnu Chandu,
Student, Faculty of Science and Engineering, Auckland University of Technology,
Auckland; Manaia Laulu, Student, Department of Applied Science, Auckland
University of Technology, Auckland; David Simmons, Professor, Waikato Clinical
School, University of Auckland, Hamilton; Boyd Swinburn, Professor, Physical
Activity and Nutrition Research Unit, School of Health Sciences, Deakin
University, Melbourne, Australia; ChittaranjanYajnik, Director, Diabetes Unit,
KEM Hospital Research Centre, Pune, India
Acknowledgements:
This research was supported, in part, by the Auckland University of Technology,
the Public Health Commission, and the Health Research Council of New Zealand
(grant number 99/660).
Correspondence:
Associate Professor Elaine Rush, Faculty of Health, Auckland University of
Technology, Private Bag 92006, Auckland. Fax: (09) 917 9973; email: elaine.rush@aut.ac.nz
References:
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