SHORT COMMUNICATION

Very low levels of energy expenditure among pre-adolescentMexican-American girls

LARA R. DUGAS1, KARA EBERSOLE1, DALE SCHOELLER2, JACK A. YANOVSKI3,

SIMON BARQUERA4, JUAN RIVERA4, RAMON DURAZO-ARZIVU1 & AMY LUKE1

1Department of Preventive Medicine and Epidemiology, Loyola University Chicago, Stritch School of Medicine, Maywood,

IL, 2Department of Nutritional Sciences, University of Wisconsin-Madison, Madison, WI, 3Unit on Growth and Obesity,

Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of

Health, Bethesda, MD, 4Instituto Nacional de Salud Publica, Cuernavaca, Mexico

AbstractWe assessed activity energy expenditure (AEE) in Mexican-American (MA) and European-American (EA) children. Totalenergy expenditure (TEE) was measured using the doubly-labeled water method; AEE was calculated as the differencebetween TEE and resting EE (REE), and physical activity level (PAL) was calculated as TEE/REE. Groups werecomparable for age, sex and body mass index (BMI). REE did not differ between groups. The boys did not differ in TEE,AEE, or PAL (MA vs. EA, respectively: TEE, 7.991.5 vs. 7.590.9 MJ.d�1; AEE: 64.9924.7 vs. 65.3922.3 kJ.kg�1.d�1;PAL: 1.5790.18 vs. 1.5890.19 kJ.kg�1.d�1). MA girls had lower TEE, AEE, and PAL than EA girls (TEE: 6.890.9 vs.8.190.8 MJ.d�1; AEE, 37.3915.9 vs. 64.9924.7 kJ.kg�1.d�1; PAL, 1.4090.12 vs. 1.5790.18; PB0.005). Resultssuggest that these MA girls were expending less energy than EA children of comparable body size due to a reduced activityenergy expenditure.

Key words: Physical activity energy expenditure, doubly�labeled water, ethnicity

Introduction

According to data from the National Health and

Nutrition Examination Survey, 1999�2004, child-

hood overweight, defined as ]95 percentile of BMI-

for-age, is highly prevalent in the predominant ethnic

groups in the United States. Among the highest rates

are Mexican-American (MA) children (22.0% and

16.2% for boys and girls, respectively) and African-

American children (16.4% and 23.8%), when com-

pared with European-American (EA) children (17.8

and 14.8%) (1). The reasons for sex and ethnic

differences remain controversial. Some studies re-

port differences in the components comprising

energy expenditure (EE) between the sexes or ethnic

groups (2�6), while others attribute differences to

behavioral lifestyle factors, such as differential parti-

cipation in organized sports (7,8) or non-equivalent

familial environments (9). The aim of the current

study was to perform a preliminary investigation of

EE in healthy MA and EA children and to determine

if EE was differentially associated with adiposity

between the groups.

Research methods and procedures

The site samples included twenty first-generation MA

children from the western suburbs of Chicago, IL and

seventeen EA children from Bethesda, Maryland,

aged 6�10 years. The MA study was approved by the

Institutional Review Board of the Loyola University,

Chicago, IL, and the EA study was approved by the

National Institute of Child Health and Human

Development (NICHD) Institutional Review Board

(www.clinicaltrials.gov NCT00001522).

Body composition was measured by the stable

isotope-dilution method, using the average of the

deuterium and 18O dilution spaces (10). Fat-free

Correspondence: Lara Dugas, Department of Preventive Medicine and Epidemiology, Loyola University School of Medicine, 2160 S. First Avenue, Building

105, Maywood, Illinois, 60153, USA. Fax: 1 708 327 9009. E-mail: ldugas@lumc.edu

International Journal of Pediatric Obesity. 2008; 3: 123�126

(Received 4 August 2007; accepted 9 January 2008)

ISSN Print 1747-7166 ISSN Online 1747-7174 # 2008 Taylor & Francis

DOI: 10.1080/17477160801902248

mass (FFM) was calculated by dividing the average

total body water by a pediatric age-specific hydration

constant (11). Fat mass (FM) was calculated as the

difference between body weight and FFM. Height

was measured to the nearest 0.1 cm using a wall-

mounted stadiometer and body weight was mea-

sured to the nearest 0.1 kg using a calibrated

electronic scale (Seca Corp, San Jose, CA and

Scale-Tronix, Wheaton, IL). Height and weight

measurements were used to calculate BMI as weight

(in kg)/height2 (in m).

Energy expenditure

REE (MJ.d�1) was measured for ]30 minutes,

using the DeltaTrac II, (Viasys Medical Systems,

Palm Springs, CA), early in the morning, following

an overnight fast to determine the average REE

(MJ.d�1) using the equations of Weir (12). TEE

(MJ.d�1) was measured over a period of either 7

(Bethesda-based cohort) or 14 days (Chicago-based

cohort) using the doubly-labeled water (DLW)

technique, as previously described (13). The length

of the measurement period did not influence the

outcome of the study. Sampling procedures were

identical for both the MA and EA participants and

all samples were analyzed at the same laboratory

(14). AEE was calculated as: AEE�(0.94�TEE �REE) (15,16). The physical activity level (PAL) was

calculated as the ratio of TEE to REE (17).

Statistical methods

The primary outcomes were the relationship be-

tween ethnicity and components of energy expendi-

ture, evaluated in an analysis of variance performed

using Stata/SE (Version 9.0; StataCorp LP, College

Station, TX), after adjustment for sex and body

weight. Two sets of multivariate regression analyses

were performed: 1) to determine the predictors of

REE, TEE and AEE using age, body weight, FFM,

percent body fat and ethnicity as independent

variables, and 2) to assess the association between

percent body fat and AEE, sex and ethnicity after

controlling for body weight.

Results

The sample included 47 children, of which 20 were

MA (10 girls and 10 boys) and 27 were EA (11 girls

and 16 boys). Participant characteristics (Table I)

were comparable for age, weight, BMI, FFM, and

percent body fat. REE adjusted for covariates was

not significantly different among groups.

MA children had a significantly lower TEE than

EA children (Table I, PB0.05), primarily due to a

difference in the TEE in MA girls (PB0.01). Age,

weight, percent body fat, and FFM were all sig-

nificant contributors to the final regression model for

TEE (PB0.001). AEE was also influenced by

ethnicity, with the MA children having significantly

lower levels than the EA children (Table I, PB0.01),

also almost exclusively due to the lower AEE in the

MA girls (PB0.005). Differences remained signifi-

cant between MA and EA girls after AEE was

adjusted for body weight (PB0.005) or FFM (PB

0.01). PAL was similarly influenced by ethnicity with

MA girls having significantly lower levels of PAL

than the EA girls (PB0.005).

Percent body fat was inversely associated with

AEE adjusted for body weight (r��0.43, pB0.01).

Table I. Participant characteristics for Mexican American (MA) and European American (EA) girls and boys.

Girls Boys

MA EA MA EA

N 10 11 10 16

Age (year) 8.391.2 8.191.0 7.691.0 8.091.0

Height (cm) 132.099.2 132.898.1 127.794.2 129.496.7

Weight (kg) 36.6911.2 35.496.9 31.496.1 32.197.3

BMI (kg/m2) 20.794.4 19.992.4 19.192.9 19.093.0

Fat-free Mass (kg) 23.194.5 24.493.7 21.692.5 22.993.6

% Body fat 34.799.7 30.097.9 29.897.8 27.497.8

TEE (MJd-1) 6.8690.93a 8.0990.84b 7.5590.90 7.9291.50b

REE (MJd-1) 4.9990.64 4.9290.55 4.9190.46 4.9990.58

TEF (MJd-1) 0.4190.06 0.4990.05 0.4590.05 0.4890.09

AEE (MJd-1) 1.4790.61a 2.6890.89b 2.1990.78b 2.4691.00b

AEE (kJ.kg-1d-1) 42.6918.2a 79.3931.3b 71.4927.4b 75.1922.9b

PAL 1.4090.12a 1.6690.22b 1.5790.18b 1.5890.19b

Note: Characteristics with differing superscripts are significantly different, pB0.05. TEE�Total Energy Expenditure, REE�Resting

Energy Expenditure, TEF�Thermic Effect of Food, AEE�Activity Energy Expenditure, PAL�Physical Activity Level.

124 L. R. Dugas et al.

This association did not differ between sex or

ethnicity.

Discussion

We found that AEE was significantly lower in MA

girls, compared with EA girls and boys and con-

tributed to an overall significantly lower TEE in the

MA children compared with the EA children. In

addition, adiposity was similarly inversely associated

with AEE among girls and boys, and between ethnic

groups. Fontvieille et al. (2) reported similar ob-

servations in Pima Indians: Pima Indian girls en-

gaged in lower levels of leisure time physical activity

(PB0.01) than EA girls. Unlike the current study,

lower EE was also found in Pima Indian compared

with EA boys, and in part, explained the higher

adiposity reported in these Pima Indians. While in a

more recent study comparing only MA boys and

girls (18), physical activity was consistently lower in

MA girls, independent of age (PB0.001). In our

small study, the MA and EA children were similar in

age and BMI, therefore, we anticipated that AEE

would be comparable between the groups.

One possible explanation for the AEE discrepancy

may be found in recent data examining physical

activity behavior amongst minority children. Gor-

don-Larsen et al. (19) found the number of adoles-

cents participating in the recommended amount of

physical activity bouts per week to be similar

amongst MA, African-American, and EA boys,

whereas amongst the girls, a significantly lower

number of MA and African-American girls met the

recommended physical activity guidelines compared

with the EA girls. Although data on school-year

versus summer measurements are not reported here,

almost equal numbers of MA and EA children were

examined during each period. For both MA and EA

children, there was higher AEE during the summer

(increase of 46.2% and 18.9%, respectively). MA

girls had the lowest AEE regardless of when the

measurement was made. An obvious explanation for

the difference between MA and EA are the seasonal

temperature variation in Chicago compared with

Bethesda. The published reports on this topic

provide mixed results: studies showing either higher

levels of physical activity during the school-year (20),

during summer (21) or little difference by season

(22,23). However, our data are suggestive that sex-

specific cultural issues and seasonality may be

important influences on AEE, particularly for MA

children.

Limitations of the current preliminary study are

that data were collected at two research sites and that

socio-demographic variables, which may impact

upon physical activity patterns, were not available

for study. The magnitude of the observed effects,

i.e., 45% lower AEE between MA and EA girls and

37% lower AEE between MA girls and both samples

of boys, suggests further investigation on AEE and

physical activity patterns among urban MA children

may well be warranted.

In conclusion, this preliminary study suggests MA

girls may expend less energy than EA girls of

comparable body size due to reduced AEE. Lower

EE may be an important determinant of body weight

later during adolescence and adulthood and, there-

fore, provide a conceivable explanation for the

difference in obesity rates observed between MA

and EA women.

Acknowledgements

Mr. Tim Shriver from the Stable Isotope Core

Laboratory, University of Wisconsin, Madison, Wis-

consin is thanked for the analysis of the DLW

samples and the staffs of the Maywood and Bethesda

clinics are thanked for their assistance with the

sample collections. J.A.Y. is a Commissioned Officer

in the US Public Health Service.

This study was funded by: the National Insti-

tutes of Health R01 DK30031 (D.A.S.); the Intra-

mural Research Program of the National Institutes

of Health, Grant Z01-HD-00641 (NICHD) (J.A.Y.)

supplemental funding from the National Center for

Minority Health and Health Disparities (J.A.Y.); and

internal support from Loyola University Stritch

School of Medicine (A.L.).

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