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American Journal of Clinical Nutrition, Vol. 69, No. 1, 43-48, January 1999
© 1999 American Society for Clinical Nutrition

Original Research Communications

Energy expenditure of young Polynesian and European women in New Zealand and relations to body composition1,2,3

Elaine C Rush, Lindsay D Plank and W Andrew Coward


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Reduced energy expenditure and excessive energy intake have been hypothesized to cause obesity. New Zealanders of Polynesian origin have a higher prevalence of obesity than do those of European origin.

Objective: We investigated relations between components of energy expenditure and body composition.

Design: We measured total energy expenditure (TEE) and resting metabolic rate (RMR) in 80 young women [40 New Zealand (NZ) Polynesian and 40 NZ European] aged 18–27 y by the doubly labeled water method and indirect calorimetry, respectively. Each group was partitioned into nonobese and obese on the basis of percentage body fat.

Results: TEE and body weight were highly correlated in nonobese NZ Europeans (n = 23, r = 0.76, P < 0.001), obese NZ Europeans (r = 0.58, P = 0.016), and nonobese NZ Polynesians (n = 25, r = 0.59, P = 0.002) but not in obese NZ Polynesians (r = 0.11, P = 0.70). Activity energy expenditure (AEE = TEE - RMR) was similar in obese Polynesians and Europeans (x ± SD: 5.5 ± 2.2 and 5.2 ± 1.9 MJ/d, respectively), but significantly higher in nonobese Polynesians (5.7 ± 2.5 MJ/d) than in their European counterparts (3.8 ± 1.9 MJ/d, P = 0.005). Similar trends were seen when AEE adjusted for body weight and TEE/RMR were compared among the subgroups. Body weight and RMR together accounted for 66% of the variation in TEE for the European group but only 17% for the Polynesian group.

Conclusion: Care should be taken in applying "Caucasian norms" relating to energy expenditure to NZ Polynesian people.

Key Words: Doubly labeled water • indirect calorimetry • obesity • ethnicity • resting metabolic rate • total energy expenditure • activity energy expenditure • fat mass • New Zealand Polynesians • New Zealand Europeans • women


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In New Zealand, the overall prevalence of obesity, defined as a body mass index (in kg/m2) >30, is increasing (1). Female New Zealanders of Polynesian origin have at least twice the prevalence of obesity (2, 3) and up to 4 times the prevalence of type 2 diabetes (4) as do women of European origin. It has been suggested (5) that a high predisposition to obesity in New Zealand Polynesian people may reflect an evolutionary development in energy storage metabolism, resulting in conservation of energy during famines and efficient fat deposition in times of food abundance. This "thrifty genotype," originally hypothesized by Neel (6), may help explain the increasing prevalence of obesity in New Zealanders of Polynesian origin (2) when considered in the context of changes in diet, physical activity, and other unidentified factors in a new, affluent culture and country. In a national census questionnaire, those identifying themselves as of Pacific Island or Maori descent reported lower amounts of leisure time physical activity than other New Zealanders (7), but objective measures of physical activity have not been taken in New Zealand.

The question of whether obese persons are less active than nonobese persons has been addressed by several investigators. Schoeller and Fjeld (8) reviewed energy requirements, physical activity, and the effects of overfeeding in obese subjects as measured by the doubly labeled water technique and confirmed that obese subjects generally expended more energy than lean control subjects and that the increase was in proportion to fat-free mass (FFM). This result was confirmed by Welle et al (9), who showed that the energy expended by a group of overweight women did not differ significantly from that expended by normal-weight women when the data were adjusted for weight or lean body mass.

In the present study, we investigated and compared the relations between total energy expenditure (TEE) measured over a period of 14 d by the doubly labeled water technique, resting metabolic rate (RMR), and body composition in young New Zealand women of European or Polynesian origin. In this paper, the term New Zealand Polynesian includes people born in New Zealand who are descendants of the New Zealand Maori, Tongan, Samoan, Cook Island Maori, and Niuean ethnic groups. Pooling these ethnic groups does not imply biological homogeneity but New Zealanders from these ethnic groups all share ancestry that has adapted to the vast Pacific Ocean environment. Similarly, the term New Zealand European refers to a geographic division of people originating from the vast land mass of Europe.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Subjects
The study was approved by the University of Auckland Human Subjects Ethics Committee and the Auckland Institute of Technology Ethics Committee. Study subjects were 82 healthy, female volunteers aged between 18 and 27 y, living in urban Auckland, and selected for ethnicity and body size by personal contact and advertisement. All subjects gave their free and informed consent. Subjects who were pregnant or lactating, currently dieting, or not maintaining a stable body weight were excluded. Measured resting blood pressure and fasting blood glucose were within normal limits for all subjects, ie, diastolic blood pressure was not >90 mm Hg and fasting blood glucose was <5.7 mmol/L. Forty-two of the volunteers identified themselves as New Zealand (NZ) European and 40 as NZ Polynesian (22 Samoan, 12 Maori, 3 Tongan, 2 Niuean, and 1 Cook Islander). Body mass index exceeded 30 in 20 of the NZ Europeans and 21 of the NZ Polynesians.

Total energy expenditure
TEE was measured over a 14-d period by the doubly labeled water technique. After a baseline urine sample was collected, each subject ingested a single dose of doubly labeled water (10.16 atom% H218O and 9.05 atom% 2H2O; Enritech Enrichment Technologies, Rehovot, Israel) at a dose of 1.5 g/kg FFM. This estimate of FFM was obtained from measured weight and body fat as determined from girth measurements (10), which are easily obtained and associated with less measurement error than skinfold thicknesses, particularly in obese subjects (11). The dose, weighed in grams to 4 decimal places with a high-precision balance, was followed by two 50-mL washes of the container with tap water. A subsample of the dose was diluted 500 times with water and stored with the urine samples in the same type of container. Urine was collected 4 and 5 h after dosing. The subjects were given sampling containers and instructions to collect timed urine samples 2 and 5 d later, and on the mornings of days 7 and 14 the subjects reported to the laboratory for further sample collection. Urine samples (50 mL) were stored at -21°C until analyzed by isotope ratio mass spectrometry.

The 18O isotope enrichments were determined on a Tracer Mass isotope ratio mass spectrometer (Europa Scientific, Crewe, United Kingdom). A 1-mL portion of each well-mixed urine sample was injected into evacuated glass tubes (7 mL) filled with carbon dioxide gas. Three replicates of each baseline urine sample and one each of the other timed samples were prepared, as were 1-mL portions of the diluted dose. The tubes were equilibrated overnight (12 h) in a 24°C water bath. A 0.7-mL sample of the equilibrated head space gas was sucked into a 1-mL tuberculin syringe and injected into the mass spectrometer. To minimize memory effects (12), samples from each subject were analyzed in order of expected increasing enrichment, ie, baseline; days 14, 7, 5, and 2; 5 and 4 h; diluted dose; and standard water. The 18O content of the urine was calculated according to International Atomic Energy Agency recommendations (13).

Baseline urine samples (in triplicate), all other timed samples, standard water, the diluted dose, and standard urine samples were analyzed for deuterium enrichment by the zinc-reduction method. Briefly, heat-resistant glass tubes, with a 6-mm outer diameter and <20 cm long, were filled with 180–200 mg dry Zn (Department of Geochemistry, Indiana University, Bloomington) and attached to a vacuum pump while being heated to 450°C for 2 min to remove residual moisture. The tubes were backfilled with pure nitrogen and then a 5-µL capillary filled with the well-mixed urine or water samples was quickly dropped into the tube. The tube was then reattached and immersed in liquid nitrogen for 1 min and evacuated. The tubes were flame sealed and stored at -21°C until measurement on a VG Micromass 602 mass spectrometer (Middlewich, United Kingdom). Immediately before analysis, the tubes were heated for 30 min in a block heater to reduce the water to hydrogen gas. The lower third of the tube including the zinc was heated to 505°C while the upper portion was kept above 70°C to prevent condensation of the water vapor. Samples were compared with a reference hydrogen gas that was calibrated daily against laboratory water standards. The machine H3+ correction was also checked daily before any samples were analyzed. Samples were analyzed in the order of expected increasing enrichment for each subject, ie, baseline; days 14, 7, 5, and 2; 5 and 4 h; diluted dose; and internal standard.

Mean daily carbon dioxide production was calculated from the 4- and 5-h and 2-, 5-, 7-, and 14-d isotopic enrichments by using the multipoint (slope intercept) method as described elsewhere (14, 15). Dilution spaces for 2H and 18O were determined from the zero-time intercept of the linear regression equation generated for all data points after logarithmic transformation. The food quotient, determined from 7-d diaries of food intake over the first week of the 14-d study period, was assumed to be equivalent to the respiratory quotient and the energy equivalent for each mole of carbon dioxide produced was converted to kJ/L by using the formula of Elia and Livesey (16).

Resting metabolic rate
RMR was measured after an overnight fast by using indirect calorimetry on day 14 as described in detail previously (17). Briefly, two 5-min expired air collections were obtained in Douglas bags after each subject was familiarized with the required procedure and her heart rate had been stable for >=10 min. Immediately after the procedure was completed, the collected expired gas was sampled sequentially from each bag and then passed at 200 mL/min through, in turn, a small tube containing granulated anhydrous magnesium perchlorate, a paramagnetic oxygen analyzer (Servomex OA570; Sybrom-Taylor Instrument Analytics Ltd, Crowborough, United Kingdom), and an infrared carbon dioxide analyzer (Medical Gas Analyzer LB2; Beckman Instruments Ltd, Fullerton, CA). The volume of gas in each Douglas bag was measured by drawing the gas through a coal gas meter. Volumes sampled for gas analyses were added to the volumes measured. Oxygen uptake ({bullet}VO2) and carbon dioxide consumption ({bullet}VCO2) were calculated and the respiratory exchange ratio derived. In a steady state, the respiratory exchange ratio is equal to the respiratory quotient. Resting oxygen uptake was taken as the average of the two 5-min collections and converted to energy consumption by multiplying by the thermal equivalent of oxygen for the calculated respiratory quotient (18). Subjects were asked not to change their normal pattern of exercise the day before the RMR measurement (because this was part of the 14-d measurement of TEE) and refrained from exercise for >=12 h before the measurement.

Activity energy expenditure
Activity-related energy expenditure (AEE) was calculated as the difference between TEE and RMR. No correction was made for the thermic effect of food.

Anthropometry and body composition
At each subject's first visit to the laboratory, standing height was measured to 0.1 cm with a stadiometer (Kawe; Asperg, Germany) and weight was measured to 0.025 kg on a beam balance (Avery, Birmingham, United Kingdom). Skinfold thicknesses (triceps and subscapular) and waist and hip circumferences were obtained as described previously (19). All measurements were made by a single observer (ECR). Total body water was assumed to be given by the 18O dilution space divided by 1.01 (20). Technically, the 18O space can be measured with better precision and accuracy than the deuterium space, particularly when the zinc method is used to measure deuterium (14). FFM was derived from total body water by assuming that FFM was 73% hydrated. Fat mass was calculated as the difference between total body weight and FFM. A BMI >30 is usually taken to indicate obesity in white subjects. We reported previously (19) that this threshold corresponded to 42% body fat in the NZ Europeans in the present study. This amount of body fat (as a percentage of body weight) was used to partition the 2 ethnic groups into obese and nonobese subgroups. A BMI of 34 for the NZ Polynesians equaled 42% body fat (19).

Statistical analysis
Statistical analyses were performed by using SAS (version 6.04; SAS Institute Inc, Cary, NC). Student's t test was used to compare selected variables between groups. Bivariate correlations were assessed by using Pearson's correlation coefficient. Chi-square was used to test whether stage of menstrual cycle was distributed similarly in the 2 ethnic groups. Regression relations were compared by using analysis of variance (ANOVA) to test for homogeneity of slopes. Two-way ANOVA was used to examine interactions between ethnicity and obesity for selected variables. Determinants of TEE were assessed by stepwise multiple regression analysis. The 5% level was chosen for statistical significance. Results are expressed as means ± SDs unless stated otherwise.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Of the 82 subjects recruited, 2 NZ European subjects failed to provide appropriately timed urine samples. Values for all variables for the 80 subjects who completed the protocol are presented in Table 1Go. Total body fat and percentage body fat were not significantly different between the 2 ethnic groups but the Polynesian women tended to be heavier, as reflected in their significantly higher FFM (P = 0.0002). Waist-to-hip ratio was almost identical for the 2 groups but the higher subscapular-to-triceps skinfold-thickness ratio (STR) in the NZ Polynesian group (P < 0.0002) indicated that the subcutaneous fat mass in this group was distributed more centrally. There was no significant difference between the ethnic groups for stage of menstrual cycle (chi-square = 0.02).


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  		TABLE 1. . Characteristics of New Zealand European and Polynesian women1
 
The mean values for the ratio of the 2H to 18O dilution spaces were not significantly different across the obese and nonobese subgroups (1.07 ± 0.02 for the European subgroups and 1.06 ± 0.02 for the Polynesian subgroups). The food quotient varied slightly from 0.85 ± 0.02 for the obese Polynesian subjects to 0.87 ± 0.02 for the nonobese European subjects. As shown in Figure 1Go, TEE and body weight were highly correlated in nonobese NZ Europeans (n = 23, r = 0.76, P < 0.001), obese NZ Europeans (n = 17, r = 0.58, P = 0.016), and nonobese NZ Polynesians (n = 25, r = 0.59, P = 0.002), but not in obese NZ Polynesians (n = 15, r = 0.11, P = 0.70). The TEE and weight ranges in the obese NZ Polynesian group were 9.9–17.9 MJ/d and 78–132 kg, respectively (Table 2Go). Although the insertion of FFM instead of body weight yielded similar results for the relation with TEE, the use of FFM here is problematic because it is not independent of TEE because both variables were calculated by using total body water. About 40% of the increase in TEE between the nonobese and obese NZ European subgroups was explained by the increase in RMR (P = 0.012) resulting from the increase in FFM (P = 0.002) in the obese subgroup. Between the NZ Polynesian nonobese and obese subgroups, the increase in RMR (P = 0 .002) was commensurate with an increase in FFM (6.1 kg, P = 0.002) similar to that observed in NZ Europeans (6.5 kg). Because AEE was similar in magnitude for the 2 Polynesian subgroups, the increase in TEE appears to have been accounted for by the change in RMR.



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  		FIGURE 1. Relations between total energy expenditure and body weight in 23 nonobese ({circ}; r = 0.76, P < 0.001) and 17 obese ({triangleup}; r = 0.58, P = 0.02) New Zealand European women and 25 nonobese ({bullet}; r = 0.59, P = 0.002) and 15 obese ({blacktriangleup}; r = 0.11, P = 0.70) New Zealand Polynesian women.

 

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  		TABLE 2. . Physical characteristics and energy expenditure data in New Zealand European and Polynesian women partitioned into nonobese and obese subgroups on the basis of percentage body fat1
 
The correlation coefficients between TEE and RMR provide information on the heterogeneity of the groups with respect to AEE. These 2 variables were much more strongly associated in the NZ European group (r = 0.78, P < 0.0001) than in the NZ Polynesian group (r = 0.38, P = 0.015). In the nonobese and obese NZ European subgroups, similar correlations between TEE and RMR were observed (r = 0.77, P < 0.0001, and r = 0.70, P = 0.002, respectively); in contrast, a significant correlation was seen in the obese NZ Polynesian subgroup (r = 0.52, P = 0.047) but not in the nonobese subgroup (r = 0.20, P = 0.34). In Figure 2Go the regression relations are shown for the natural logarithm of TEE plotted against the natural logarithm of RMR (21, 22) for the 2 ethnic groups. The slopes of these regressions differed significantly (P = 0.016). For the NZ Europeans the slope was close to unity (P = 0.42), whereas it differed significantly from unity for the NZ Polynesians (P = 0.003).



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  		FIGURE 2. Relation between the natural logarithms of total energy expenditure (TEE) and resting metabolic rate (RMR) in 40 NZ European ({circ}) and 40 New Zealand Polynesian ({bullet}) women. The linear regressions are as follows: ln(TEE) = 1.13 ln(RMR) + 0.23 (r2 = 0.58, SEE = 0.17, P < 0.0001) for the NZ Europeans (dashed line) and ln(TEE) = 0.45 ln(RMR) + 1.65 (r2 = 0.15, SEE = 0.19, P = 0.013) for the New Zealand Polynesians (solid line).

 
Compared with that in nonobese NZ Europeans, AEE was significantly higher in nonobese NZ Polynesians (P = 0.005) and obese NZ Europeans (P = 0.023; Table 2Go). To adjust AEE for differences in body size, we used body weight to the power 0.5 as the denominator (23). As shown in Table 2Go, AEE/weight0.5 was significantly higher for the nonobese NZ Polynesians than for the nonobese NZ Europeans (0.66 ± 0.27 compared with 0.47 ± 0.22 MJ{bullet}kg-0.5{bullet}d-1; P = 0.025). Values in the obese groups were not significantly different (0.54 ± 0.24 and 0.53 ± 0.18 MJ{bullet}kg-0.5{bullet}d-1 for NZ Polynesians and NZ Europeans, respectively). A similar pattern between the 4 groups was seen when physical activity was quantified by expressing TEE as a multiple of RMR (ie, physical activity level). As shown in Table 2Go, the mean physical activity level for the obese subgroups was identical in NZ Polynesians (1.71 ± 0.32; range: 1.14–2.54) and NZ Europeans (1.71 ± 0.25; range: 1.30–2.03). The difference between the nonobese NZ Polynesians (1.88 ± 0.42; range: 1.26–3.03) and the nonobese NZ Europeans (1.58 ± 0.29, range: 1.22–2.33) was not significant (P = 0.15). The two-way ANOVA for this classification of the subjects indicated an interaction between ethnicity and obesity (P = 0.054). The obese NZ Europeans tended to be more active and the obese NZ Polynesians less active than their nonobese counterparts.

Body weight and RMR together accounted for 66% of the variation in TEE for the NZ European group but only 17% for the NZ Polynesian group. For the 80 subjects as a whole, stepwise multiple regression analysis showed that RMR, body weight, and ethnicity were significant predictors of TEE (model R2 = 0.43,P < 0.05). The question of body fat distribution as a predictor of TEE was addressed by the addition of the STR to the model. This caused body weight and ethnicity to drop out as significant predictors (P > 0.15), leaving RMR and STR explaining 44% of the variation in TEE.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Hypothesized risk factors for weight gain and eventual onset of obesity include a low RMR, low TEE, and low AEE after interindividual differences in body size are accounted for (24). We reported previously that the NZ Polynesian subjects studied in the present work have a lower RMR after adjustment for FFM and fat mass than do NZ Europeans (17). We now have shown that although TEE, after adjustment for body weight, was not significantly different between these 2 ethnic groups, the tendency for AEE to increase with increased percentage body fat (reflecting increased body weight) applied to the NZ European group but not to the NZ Polynesian group. Although the nonobese NZ Polynesians appeared to be significantly more active than their NZ European counterparts, this was not true for the obese NZ Polynesians. These trends were also evident when a correction for body weight was applied to AEE and when physical activity level was compared among the subgroups. We cannot explain this difference because to the best of our knowledge the ethnic groups were matched for lifestyle influences. In agreement with others (21, 25–27), we showed that the TEE of our European subjects was significantly correlated with body mass, FFM, and RMR. The important new finding was that the body-composition determinants of energy expenditure for European women did not apply to the NZ Polynesian women in our study.

AEE and its relation to body mass depend on whether the activity is weight-bearing or not (23). On the basis of the suggestion of Prentice et al (23), we adjusted AEE for body size effects by dividing by the square root of body weight, which is expected to be more appropriate for a mix of weight-bearing and non-weight-bearing activity. Although we have no direct measure of the types of activity our subjects engaged in, 19 (13 nonobese, 6 obese) of the 40 NZ Europeans and 32 (21 nonobese, 11 obese) of the 40 NZ Polynesians were students. Except for 1 subject in each ethnic group, the remainder were technicians or had secretarial occupations.

Any study of energy expenditure in females is confounded by changes in energy expenditure related to the menstrual cycle. Webb (28) showed that in the luteal phase of the menstrual cycle, TEE increases on the order of 8–16%. This change is not seen with the intake of oral contraceptives. Furthermore, when considering the variability in a study group of young women, one must also take into account that body water changes in response to cyclic hormonal changes. Appetite and body water both increase in the luteal phase. In this study, there was no significant difference in stage of cycle between the 2 ethnic groups.

Body weight and FFM were strong predictors of TEE in both ethnic groups but body-composition variables for the NZ European group had much higher correlations with TEE and RMR than did those for the NZ Polynesian group. Similarly, RMR and the STR had a tighter linear relation with TEE for the NZ European than for the NZ Polynesian group. We avoided direct assessment of the associations between variables such as TEE and body fat, which are interdependent because both are based on measurement of total body water. However, it was clearly evident that the NZ Polynesian women in this study did not fit the same pattern as the NZ European women and that care should be taken in applying "Caucasian norms" relating to energy expenditure to NZ Polynesians.

Central adiposity measured as the STR has been shown to be associated with the insulin-resistance syndrome, syndrome X (29). We showed that in both ethnic groups studied, the STR was significantly higher in obese subjects. The STR was also significantly elevated in the Polynesian subgroups compared with the European subgroups. Multiple regression analyses showed that STR behaved as a surrogate for ethnicity in relations between energy expenditure and body composition. Further studies are needed to determine more precisely the extent of centralized adiposity in Polynesian compared with European subjects.

It was disturbing to find that in the young NZ Polynesian women in this study, those who were categorized as obese had lost the tight association between components of energy expenditure and body size that was observed in their European counterparts. This has implications for formulating recommendations for energy intake and physical activity for obese NZ Polynesian women. Our findings provide further evidence for an evolutionary adaptation in NZ Polynesians toward metabolic efficiency in fat deposition.


   ACKNOWLEDGMENTS
 
We thank Manaia Laulu for assistance with the measurements and the subjects for their cooperation.


   FOOTNOTES
 
1 From the Department of Applied Science, Auckland Institute of Technology, and the Department of Surgery, University of Auckland, Auckland, New Zealand, and the Dunn Clinical Nutrition Centre, Cambridge, United Kingdom.

2 Supported by grants from the Auckland Institute of Technology Contestable Research Fund and the Health Research Council of New Zealand.

3 Reprints not available. Address correspondence to EC Rush, Department of Applied Science, Auckland Institute of Technology, Private Bag 92006, Wellesley Street, Auckland, New Zealand. E-mail: elaine.rush{at}ait.ac.nz.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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Received for publication January 7, 1998. Accepted for publication June 22, 1998.




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D. A. Schoeller
Recent Advances from Application of Doubly Labeled Water to Measurement of Human Energy Expenditure
J. Nutr., October 1, 1999; 129(10): 1765 - 1768.
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