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Original Studies |
Department of Medicine, Division of Gerontology, University of Maryland, Geriatric Research, Education and Clinical Center, Baltimore Veterans Affairs Medical Center (M.J.T., E.T.P.), Baltimore, Maryland 21201; and the Department of Medicine, Division of Clinical Pharmacology and Metabolic Research, University of Vermont (R.D.S., M.J.T., D.E.M., E.T.P.), Burlington, Vermont 05405
Address all correspondence and requests for reprints to: Eric T. Poehlman, Ph.D., Department of Medicine, University of Vermont, Given Building C-247, Burlington, Vermont 05405. E-mail: epoehlma{at}zoo.uvm.edu
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Abstract |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Daily energy requirements to maintain optimal levels of body composition and nutritional status in elderly African-Americans are unknown. Although current energy requirements recommendations are estimated at 1.51 times the RMR (9), these data were collected in Caucasians and do not consider the heterogeneity of daily energy needs with advancing age. Moreover, recent research suggests that these guidelines underestimate daily energy needs in elderly Caucasians (10). Recent data also demonstrate that older African-Americans, particularly African-American women, have lower daily energy expenditure for their "metabolic size" than older Caucasians (11). Indeed, if daily energy expenditure is inappropriately low in this population, an apparently normal consumption of calories will result in a positive energy balance and an accelerated accumulation of body fat. Based on these preliminary findings, ethnic-specific energy requirement recommendations may be needed for older African-Americans.
Thus, the primary aim of this study was to determine whether daily energy requirements of older African-American women and men differ from current recommendations, and whether energy requirements differ between older African-Americans and Caucasians. As a secondary aim, we examined determinants of physical activity energy expenditure in older African-American women and men. The application of doubly labeled water methodology in combination with indirect calorimetry allows an accurate and unobtrusive assessment of physical activity energy expenditure in this understudied population. Moreover, low levels of physical activity energy expenditure are implicated in the development of obesity-related comorbidities (12, 13) and decreased functional independence (14) in the elderly.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Subjects were 65 older African-American women (n = 37) and
men (n = 28) between 52–79 yr recruited from the Baltimore, MD
area. Descriptive characteristics are presented in Table 1
. A subsample of these individuals was
previously studied (11, 15, 16). Each subject was from 2 generations of
African ancestry, as determined from an interview. A group of elderly
Caucasian women (n = 51) and men (n = 48), who have been
previously described (11), were also included for a retrospective
examination of energy requirement differences between African-Americans
and Caucasians. All subjects were healthy and had no history or
evidence on physical examination of 1) coronary heart disease, 2)
hypertension, 3) medications that would affect cardiovascular function
or metabolism, 4) diabetes, 5) body mass fluctuation of more than 2 kg
the past year, 6) exercise-limiting noncardiac disease, 7) smoking, or
8) hormone replacement therapy. Each subject signed a consent form
approved by the institutional review board of the University of
Maryland before participating in the study.
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All subjects completed testing at the Geriatric Research, Education, and Clinical Center, University of Maryland. All subjects provided a baseline urine and were administered a mixed dose of doubly labeled water for measurement of total daily energy expenditure. RMR was measured at 0630 h after a 12-h overnight fast. Body composition was assessed using dual energy x-ray absorptiometry, followed by administration of the Minnesota leisure time physical activity questionnaire. Subjects returned 10 days later to provide two urine samples for doubly labeled water analysis and complete an aerobic capacity test. Specific details about all data collection are provided below.
RMR. RMR (kilocalories per day) was measured by indirect calorimetry for 45 min using the ventilated hood technique (17). Respiratory gas analysis was performed using a Deltatrac metabolic cart (Sensormedics, Yorba Linda, CA). The metabolic cart was calibrated 15 min before respiratory gas collection using room air and a known calibrant gas concentration (96% oxygen and 4% carbon dioxide). RMR was also estimated from body mass and height using gender-specific equations (9).
Total daily energy expenditure. Total daily energy expenditure was measured over a 10-day period using the doubly labeled water (2H218O) method of Schoeller (18). Subjects arrived on day 0, and a urine sample was acquired for measurement of baseline 2H and 18O enrichment. Between 1200–1600 h a premixed dose containing approximately 0.078 g 2H2O and 0.092 g H218O/kg body mass was given to each subject to drink. Two urine samples were collected the next morning (day 1), and two additional urine samples were collected on day 10. These urine samples were obtained between 0800–1200 h. Aliquots of the urine samples were stored frozen at -20 C in Vacutainers (Becton Dickinson, Franklin Lakes, NJ) until later analysis by isotope ratio mass spectrometry.
For measurement of 18O, duplicate 1-mL aliquots of urine were placed in Vacutainers, which were then filled with a low pressure of CO2 and shaken at room temperature overnight. The CO2 oxygen equilibrated with the water oxygen, and the 18O isotopic enrichment of the CO2 was then measured by isotope ratio mass spectrometry. For measurement of 2H enrichment, triplicate 5-µL aliquots of urine were placed in stopcock-sealed reaction vessels containing 100 mg zinc catalyst following the method of Wong et al. (19). The vessels were sealed under nitrogen gas and evacuated with the water frozen, and the water was reduced to hydrogen gas by heating the vessels in a block at 500 C for 30 min. The 2H enrichments of the hydrogen samples were measured by isotope ratio mass spectrometry on the same day they were prepared. Aliquots of the 2H218O dose were also measured for 2H and 18O enrichment after being quantitatively diluted with unlabeled water. The urine sample 2H and 18O enrichments were calculated using the diluted dose 2H and 18O enrichments as calibrants for each study’s analysis.
Determination of total daily energy expenditure. A linear regression analysis was performed on the 2H and 18O tracer enrichments transformed as the natural logarithm against time. The slopes (d-1) of the regression lines are the rates of 18O and 2H loss from body water (kO and kH, respectively). The 18O and 2H dilution spaces (NO and NH, respectively) were determined by dividing the dose of administered tracer (as moles of 2H- or 18O-water) by the intercepts (2H and 18O enrichments at time zero). Total body water (N) in moles was calculated by taking the average of the dilution space of the 18O and 2H tracers: N = 1/2 (NO/cO + NH/c'H), where cO and c'H are the sizes of the exchangeable oxygen and hydrogen pool sizes relative to total body weight. The rationale for calculating average total body water has been previously discussed (24). The 18O dilution space relative to total body water, cO, was assumed to be 1.01 (20, 21, 22). The 2H dilution space relative to total body water, c'H, was assumed to be 1.053 (23). The latter value includes all analytical methodology effects of hydrogen sample preparation and is consistent in our hands, where the c'1H/cO ratio is 1.046 ± 0.002, averaging the results of more than 250 studies.
The rate of CO2 production (rCO2; moles per day) was calculated using Eq 3 of Speakman et al. (22): rCO2 = N/2.196/(cOkO - cHkH), where cH is the true hydrogen dilution space parameter (i.e. does not contain any analytical method induced component). Following the recommendation of Racette et al. (21), values of 1.041 and 1.007 were used for cH and cO, respectively. If a value of 1.053 had been used instead for cH, the cOkO -cHkH difference would have been decreased by about 1%, and the calculation of rCO2 would have been decreased by 5% or less (24).
Assuming an RQ of the food consumed of 0.85, total CO2 production was converted to oxygen consumed, or total daily energy expenditure using the Weir formula (25): total daily energy expenditure (kcal/d) = (3.044/0.85 + 1.104) rCO2.
Determination of physical activity energy expenditure. Physical activity energy expenditure was calculated using the following equation, as previously described (26): physical activity energy expenditure (kcal/d) = (0.90 x total daily energy expenditure) - RMR. This approach assumes that the thermic effect of feeding is 10% of the total daily energy expenditure in the elderly (27).
Determination of physical activity level ratio. A physical activity level ratio was calculated for each subject by dividing the measured RMR into the total daily energy expenditure. The physical activity level ratio represents a convenient method to categorize an individual’s total daily energy expenditure or energy requirements as a multiple of RMR. This method accounts for interindividual differences in body mass by examining the ratio of total daily energy expenditure to RMR. Current energy requirement recommendations suggest a physical activity level ratio of 1.51 for individuals over 50 yr of age (9).
Body composition. Dual energy x-ray absorptiometry was used to assess body composition (DPX-L densitometer, Lunar Radiation Corp., Madison, WI). A total body scan was completed in 40 min, and analysis provided measures of fat-free mass, fat mass, and percent body fat (Lunar software version 1.3z). The coefficients of variation for repeat determinations of fat mass and fat-free mass in a subgroup of seven women were 1% and 2%, respectively.
Aerobic capacity and leisure time physical activity. Maximal oxygen consumption (VO2max) was determined during an incremental treadmill test. Treadmill speed was set at a brisk walking pace for 2 min, with subsequent increases in treadmill grade of 2.5% every 2 min until volitional fatigue. Respiratory gases were analyzed using a Sensormedics 2900 metabolic cart (Sensormedics, Yorba Linda, CA). VO2max (liters per min) was considered to be achieved with a respiratory exchange ratio greater than 1.1, a plateau of oxygen consumption with a further increase in workload, and a heart rate at or above the age-related predicted maximum (220 - age). Leisure time physical activity was measured by the Minnesota questionnaire and interview (28).
Statistical analyses. All data are expressed as the mean ± SD. Significance was accepted at the P < 0.05 level. Differences between African-American women and men for all dependent variables were examined using independent t tests. Comparison of VO2max values between African-American women and men was completed after normalizing for fat-free mass using analysis of covariance (ANCOVA) (29). One-sample t tests were used to determine whether the physical activity level ratios for African-American women and men were different from the Food and Agriculture Organization/World Health Organization/United Nations University recommendation (9). A two-way ANOVA was completed to examine potential race and gender effects for the physical activity level ratio in older African-Americans and Caucasians.
Pearson product-moment correlations were calculated to examine relationships between physical activity energy expenditure and other selected dependent variables for African-American women and men. Physical activity energy expenditure was also correlated with various dependent variables using partial correlation analyses to account for the influence of body composition on physical activity energy expenditure (30).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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shows that African-American men were taller and had
greater fat-free mass and leisure time physical activity than
African-American women, but the two groups were not different in age or
VO2max corrected for fat-free mass. Fat mass, body fat
percentage, and body mass index were greater for women compared to
men.
Measured total daily energy expenditure (2090 ± 411
vs. 2772 ± 556 kcal/d), RMR (1388 ± 227
vs. 1630 ± 205 kcal/d), and physical activity energy
expenditure (493 ± 297 vs. 865 ± 451 kcal/d)
were significantly lower in older African-American women than men,
respectively. Figure 1 shows that the
lower total daily energy expenditure persisted for women (2198 ±
621 kcal/d) compared to men (2633 ± 669 kcal/d) after adjustment
for fat and fat-free mass. RMR (1431 ± 240 vs.
1576 ± 259 kcal/d; P = 0.07) and physical
activity energy expenditure (548 ± 559 vs. 794 ±
603 kcal/d; P = 0.19) tended to be lower for women
compared to men, respectively, after adjustment for body composition
(see Fig. 1). Moreover, leisure time activity determined from the
questionnaire (see Table 1) was significantly lower than physical
activity energy expenditure determined from doubly labeled water (see
Fig. 1) in both women and men.
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) was significantly lower
(P < 0.01) for older African-American women (1.51
± 0.25) than for men (1.71 ± 0.32). One-sample t
tests demonstrated that the physical activity ratio for women was not
different than FAO/WHO/UNU recommendation (i.e. 1.51),
although the physical activity level ratio for men was
significantly higher (P < 0.01) than the
FAO/WHO/UNU recommendation. Gender differences in the physical activity
level ratio (see Fig. 2) were present (P = 0.01) for
African-American women and men and for Caucasian women (1.63 ±
0.27) and men (1.73 ± 0.28). The physical activity level ratio
tended to be lower (P = 0.13) for older
African-Americans (n = 65) than for Caucasians (n = 99).
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shows Pearson product
correlations between physical activity energy expenditure and various
dependent variables for African-American women and men. Age was the
strongest correlate with physical activity energy expenditure for
women, whereas VO2max was the strongest correlate with
physical activity energy expenditure for men.
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Discussion |
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Energy expenditure and requirements of older African-Americans
Energy requirements are most accurately determined by measuring an individual’s total daily energy expenditure (10). Application of the doubly labeled water technique allows for an objective measure of total daily energy expenditure (18) and energy requirements in free-living individuals. Current energy requirement recommendations are estimated at 1.51 times RMR for people over 50 yr of age (9). However, a recent meta-analysis shows that energy needs are higher for older Caucasians, ranging from 1.62–1.68 times the RMR (10). To our knowledge, no information is available on the adequacy of current energy requirement recommendations in elderly African-Americans.
Our data suggest that energy requirements are 1.71 times the RMR for older African-American men, which supports the idea that current recommendations underestimate actual energy needs. In contrast, energy requirements for older African-American women are similar to current recommendations (i.e. 1.51 times the RMR). Thus, if one accepts the premise that energy requirements are higher in the elderly than current recommendations (10), older African-American women have low energy needs for their body size.
A lower level of total daily energy expenditure may be one factor
contributing to the higher incidence of obesity in African-American
women compared to men (1). Total daily energy expenditure adjusted for
body composition is approximately 17% lower in African-American women
compared to men. Other investigators support a gender difference in
older Caucasians (31, 32). A lower total daily energy expenditure in
older African-American women is explained partially by a tendency
toward a lower RMR adjusted for body composition (
9%;
P = 0.07). These data are consistent with previous
reports from our laboratory that show a lower RMR in older Caucasian
women compared to men (33, 34), and now extend these findings to older
African-American women. Lower sympathetic nervous system activity (34)
and androgen hormones concentrations (35) may partially explain the
lower RMR in older women.
Low levels of leisure time physical activity are also associated with greater total and central fat gain during aging (13). Moreover, data suggest that the prevalence of sedentary behavior is 1.5 times higher among African-American women than among Caucasian women (36). Physical activity energy expenditure was measured using doubly labeled water and indirect calorimetry in the present study. This approach is more accurate than physical activity diaries and questionnaires because it is unobtrusive, does not depend on memory recall, and captures structured exercise and nonstructured movements. Our data show that physical activity energy expenditure adjusted for body composition is 31% lower in older African-American women than in men. The inability to detect statistical significance may be due to the inherent large interindividual variability in physical activity energy expenditure and/or limited statistical power.
The 246 kcal/d lower physical activity energy expenditure in African-American women is clinically relevant and could contribute to their greater body fatness and increased cardiovascular risk profile compared to African-American men. When considering the relative importance of the components of total daily energy expenditure to low energy needs in older African-American women, physical activity energy expenditure is quantitatively more important (246 kcal/d) than RMR (145 kcal/d) in explaining gender differences. This finding suggests that therapeutic interventions specifically designed to increase physical activity energy expenditure may have a significant impact on increasing total daily energy expenditure and theoretically reduce the incidence of obesity in older African-American women if compensatory changes in energy intake do not occur.
Racial and gender differences in energy requirements of the elderly
When data from our previous report (11) are considered along with those from our current study, gender-specific energy requirement recommendations should be developed to more accurately predict daily energy needs. This association is based on the findings that total daily energy expenditure adjusted for body composition (11) and the physical activity level ratio is lower in older women than in men regardless of race. In contrast, evidence for race-specific energy requirement recommendations is not as compelling. Although total daily energy expenditure and its components adjusted for body composition are lower in older African-Americans than in Caucasians (11), the physical activity level ratio only tends to be lower (4%; P = 0.13) in African-Americans compared to Caucasians during the present study. We believe that this finding is probably related to statistical power (a common problem in doubly labeled water studies), and larger sample sizes (>200 people) may reveal more convincing evidence for the establishment of race-specific energy requirement recommendations.
Determinants of physical activity energy expenditure
Despite the tendency for a lower physical activity energy expenditure in older African-American women compared to men, it is presently unclear which factors are related to lower physical activity levels. Our data show a modest, inverse relationship between age and physical activity energy expenditure in older African-American women (r = -0.44; P < 0.01). Thus, aging is associated with lower physical activity, particularly within an elderly female cohort of African-Americans. Previous data in younger Caucasian women and men (18–49 yr), however, show no association between aging and physical activity (37). Thus, aging may be more associated with lower physical activity levels in individuals above 50 yr of age, possibly due to a greater loss of skeletal muscle mass and cardiorespiratory fitness with advancing age.
Reduced cardiorespiratory fitness is associated with lower physical activity energy expenditure in older African-American men. Our data demonstrate that lower aerobic capacity is the strongest predictor of lower physical activity energy expenditure in older African-American men (r = 0.39; P < 0.05). Previous work from our laboratory shows that lower aerobic capacity is associated with lower physical activity energy expenditure in older Caucasians (26). These data demonstrate that less aerobically fit individuals may be less physically active, although it is feasible that low activity levels may also lead to reduced aerobic fitness. In either case, these results suggest that cardiorespiratory fitness serves as a proxy measure of physical activity energy expenditure in older African-American men.
The present data also show that physical activity, measured by the Minnesota leisure time physical activity questionnaire, is lower for older African-American women (-62%) and men (-48%) compared to physical activity measured by doubly labeled water and indirect calorimetry. Moreover, simple correlations demonstrate that the leisure time activity questionnaire is not related to physical activity measured from doubly labeled water. It is possible that the ability of doubly labeled water to detect nonstructured activity such as fidgeting, which is not measured in a questionnaire, may explain the lack of concordance between these two measures. These results suggest that the Minnesota leisure time physical activity questionnaire may not be useful to accurately assess free-living physical activity energy expenditure in older African-Americans.
Summary
Older African-American women appear to have energy needs that are similar to current world-wide recommendations, although energy requirements of older African-American men may be higher than current recommendations. Moreover, gender-specific energy requirement recommendations are needed for elderly African-Americans and Caucasians. In contrast, daily energy requirements tend to be lower in older African-Americans compared to Caucasians, but larger samples sizes are needed before race-specific guidelines can be recommended. Finally, physical activity energy expenditure tends to be lower in older African-American women than in men. Low free-living physical activity is associated with advancing age in older African-American women and decreased cardiorespiratory fitness in older African-American men. Public health strategies particularly aimed at increasing physical activity levels coupled with moderate caloric restriction in older African-American women should be implemented to offset their increasing prevalence of obesity and associated comorbidities.
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Acknowledgments |
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Footnotes |
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Received November 12, 1997.
Revised December 31, 1997.
Accepted February 3, 1998.
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