Measurement of physical activity among black and white obese women

Cardiovascular Risk Factors Following Vertical Sleeve Gastrectomy in Black Americans Compared with White Americans

OBJECTIVE

Bariatric surgery presents a long-term solution for clinical obesity. Given that Black Americans (BA) carry a greater burden of obesity-related comorbidities than White Americans (WA), understanding the racial disparities regarding remission of obesity comorbidities following the most common bariatric surgery, sleeve gastrectomy (SG). The goal of the current study was to provide quantitative values related to cardiovascular and lipid outcomes following SG and determine if racial disparities exist between BA and WA.

METHODS

Data was collected from de-identified electronic medical records for patients receiving SG surgery at the University of Mississippi Medical Center in Jackson, MS, USA.

RESULTS

Of 464 patients who obtained SG from (2013-2019), 64% were WA, and 36% were BA. Before surgery, BA had significantly greater body weight (BW), body mass index (BMI), and systolic (SBP) and diastolic (DBP) blood pressures (BP) in comparison with WA. Compared with WA, BA were predicted to lose 5.1 kg less BW than WA at 1-year follow-up. Reduction in SBP (- 0.96 vs. - 0.60 mmHg/doubling of days) and DBP (- 0.51 vs. - 0.26 mmHg/doubling of days) was significantly higher in WA compared with BA. There was no racial difference in the change to total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, or triglycerides by race. When normalized to weight loss, the racial disparity in BP reduction was mitigated.

CONCLUSIONS

These data indicate that BA lose less body weight following SG; however, loss of excess body weight loss is associated with improvement to BP similarly in both BA and WA.

The Role of Energy Intake on Fitness-Adjusted Racial/Ethnic Differences in Central Adiposity Using Quantile Regression

BACKGROUND

Energy intake (EI) is suggested to be associated with adiposity and may explain previously observed fitness-adjusted racial disparities in waist circumference (WC).

OBJECTIVE

The purpose of this study was to comprehensively evaluate the role of EI on the fitness-adjusted racial/ethnic disparities in WC in a nationally representative sample of females using quantile regression.

METHODS

Our sample consisted of 3874 female participants (aged 12 to 49 years) from the 1999-2004 National Health and Nutrition Examination Survey. The role of EI was assessed in separate analyses via estimation using a 24-hour dietary recall (DR) and the Institute of Medicine total daily energy expenditure equations. Age-stratified quantile regression models were used to estimate the differences in WC between minority groups and non-Hispanic (NH) white, adjusting for EI, CRF, age, and height.

RESULTS

Results from the quantile regression analyses adjusting for EI via DR showed significant differences in WC between NH black and NH white at the 25th-90th WC percentiles (5.9-11.1 cm) for females 20-49 and at the 90th WC percentile (10.1 cm) for females 16-19. For females 12-15, no significant differences were observed between NH black and NH white. Analyses adjusting for EI via IOM showed significant differences in WC between NH black and NH white only for females aged 20-49 years, at the 50th and 75th percentile (1.7-3.6 cm). Compared to NH White, Mexican American females, in all age groups, tended to have significantly greater WC.

CONCLUSIONS

These results highlight the importance of rigor in energy intake assessments, suggesting that EI, if adequately assessed, may explain a substantial part of the racial/ethnic differences in WC between NH black and NH white females. Additionally, the observed persistence of estimated differences in WC with advancing age suggests other factors (e.g., hormones) may play a role.

High energy expenditure masks low physical activity in obesity

OBJECTIVE

To investigate energy expenditure in lean and obese individuals, focusing particularly on physical activity and severely obese individuals.

DESIGN

Total daily energy expenditure (TDEE) was assessed using doubly labeled water, resting metabolic rate (RMR) by indirect calorimetry, activity energy expenditure (AEE) by difference and time spent in physical activity by multisensor activity monitors.

SUBJECTS

In all, 177 lean, Class I and severely obese individuals (age 31-56 years, body mass index 20-64 kg m(-2)) were analyzed.

RESULTS

All components of energy expenditure were elevated in obese individuals. For example, TDEE was 2404±95 kcal per day in lean and 3244±48 kcal per day in Class III obese individuals. After appropriate adjustment, RMR was similar in all groups. Analysis of AEE by body weight and obesity class indicated a lower AEE in obese individuals. Confirming lower physical activity, obese individuals spent less time engaged in moderate-to-vigorous physical activity (2.7±1.3, 1.8±0.6, 2.0±1.4 and 1.2±1.0 h per day in lean, Class I, Class II and Class III individuals) and more time in sedentary behaviors.

CONCLUSIONS

There was no indication of metabolic efficiency in even the severely obese, as adjusted RMR was similar across all groups. The higher AEE observed in the obese is consistent with a higher cost of activities due to higher body weight. However, the magnitude of the higher AEE (20-25% higher in obese individuals) is lower than expected (weight approximately 100% higher in Class III individuals). Confirming a lower volume of physical activity in the obese, the total time spent in moderate-to-vigorous physical activity and average daily metabolic equivalent of task level were lower with increasing obesity. These findings demonstrate that high body weight in obese individuals leads to a high TDEE and AEE, which masks the fact that they are less physically active, which can be influenced by duration or intensity of activity, than in lean individuals.

Do African American women require fewer calories to maintain weight?: Results from a controlled feeding trial

BACKGROUND

The high prevalence of obesity in African American (AA) women may result, in part, from a lower resting metabolic rate (RMR) than non-AA women. If true, AA women should require fewer calories than non-AA women to maintain weight. Our objective was to determine in the setting of a controlled feeding study, if AA women required fewer calories than non-AA women to maintain weight.

MATERIALS AND METHODS

This analysis includes 206 women (73% AA), aged 22-75 years, who participated in the Dietary Approaches to Stop Hypertension (DASH) trial-a multicenter, randomized, controlled, feeding study comparing the effects of 3 dietary patterns on blood pressure in individuals with prehypertension or stage 1 hypertension. After a 3-week run-in, participants were randomized to 1 of 3 dietary patterns for 8 weeks. Calorie intake was adjusted during feeding to maintain stable weight. The primary outcome of this analysis was average daily calorie (kcal) intake during feeding.

RESULTS

AA women had higher baseline weight and body mass index than non-AA women (78.4 vs 72.4 kg, P < .01; 29.0 vs 27.6 kg/m(2), P < .05, respectively). During intervention feeding, mean (SD) kcal was 2168 (293) in AA women and 2073 (284) in non-AA women. Mean intake was 94.7 kcal higher in AA women than in non-AA women (P < .05). After adjustment for potential confounders, there was no difference in caloric intake between AA and non-AA women (Δ = -2.8 kcal, P = .95).

CONCLUSION

These results do not support the view that AA women are at greater risk for obesity because they require fewer calories to maintain weight.

Energy expenditure in adults living in developing compared with industrialized countries: a meta-analysis of doubly labeled water studies

BACKGROUND

There is an assumption that people in developing countries have a higher total energy expenditure (TEE) and physical activity level (PAL) than do people in developed nations, but few objective data for this assertion exist.

OBJECTIVE

We conducted a meta-analysis of TEE and PAL by using data from countries that have a low or middle human development index (HDI) compared with those with a high HDI to better understand how energy-expenditure variables are associated with development status and population differences in body size.

DESIGN

We performed a literature search for studies in which energy expenditure was measured by using doubly labeled water. Mean data on age, weight, body mass index (BMI; in kg/m(2)), TEE, and PAL were extracted, and HDI status was assessed. Pooled estimates of the mean effect by sex were obtained, and the extent to which age, weight, HDI status, and year of publication explained heterogeneity was assessed.

RESULTS

A total of 98 studies (14 studies from low- or middle-HDI countries) that represented 183 cohorts and 4972 individuals were included. Mean (±SE) BMI was lower in countries with a low or middle HDI than in those with a high HDI for both men and women (22.7 ± 1.0 compared with 26.0 ± 0.7, respectively, in men and 24.3 ± 0.7 compared with 26.6 ± 0.4, respectively, in women). In meta-regression models, there was an inverse association of age (P < 0.001) and a positive association of weight (P < 0.001) with TEE for both sexes; there was an association of age only in men with PAL (P < 0.001). There was no association of HDI status with either TEE or PAL.

CONCLUSION

TEE adjusted for weight and age or PAL did not differ significantly between developing and industrialized countries, which calls into question the role of energy expenditure in the cause of obesity at the population level.

Population genetic analysis of the uncoupling proteins supports a role for UCP3 in human cold resistance

Production of heat via nonshivering thermogenesis (NST) is critical for temperature homeostasis in mammals. Uncoupling protein UCP1 plays a central role in NST by uncoupling the proton gradients produced in the inner membranes of mitochondria to produce heat; however, the extent to which UCP1 homologues, UCP2 and UCP3, are involved in NST is the subject of an ongoing debate. We used an evolutionary approach to test the hypotheses that variants that are associated with increased expression of these genes (UCP1 -3826A, UCP2 -866A, and UCP3 -55T) show evidence of adaptation with winter climate. To that end, we calculated correlations between allele frequencies and winter climate variables for these single-nucleotide polymorphisms (SNPs), which we genotyped in a panel of 52 worldwide populations. We found significant correlations with winter climate for UCP1 -3826G/A and UCP3 -55C/T. Further, by analyzing previously published genotype data for these SNPs, we found that the peak of the correlation for the UCP1 region occurred at the disease-associated -3826A/G variant and that the UCP3 region has a striking signal overall, with several individual SNPs showing interesting patterns, including the -55C/T variant. Resequencing of the regions in a set of three diverse population samples helped to clarify the signals that we found with the genotype data. At UCP1, the resequencing data revealed modest evidence that the haplotype carrying the -3826A variant was driven to high frequency by selection. In the UCP3 region, combining results from the climate analysis and resequencing survey suggest a more complex model in which variants on multiple haplotypes may independently be correlated with temperature. This is further supported by an excess of intermediate frequency variants in the UCP3 region in the Han Chinese population. Taken together, our results suggest that adaptation to climate influenced the global distribution of allele frequencies in UCP1 and UCP3 and provide an independent source of evidence for a role in cold resistance for UCP3.

Impact of race/ethnicity on the relationship between visceral fat and inflammatory biomarkers

The purpose of this study was to determine whether racial/ethnic differences exist in the relationship between visceral adipose tissue (VAT) and selected inflammatory biomarkers. Subjects included 136 African-American, 133 Hispanic, and 100 white men and women, aged > or =45. Waist circumference and BMI were measured using standard methods. Total VAT, and VAT and subcutaneous adipose tissue (SAT) at the L4L5 spinal level were measured using computed tomography. Interleukin-6 (IL-6), C-reactive protein (CRP), and fibrinogen were measured from fasting blood samples. Results revealed that waist circumference and BMI were similar among groups but African Americans had significantly lower L4L5 VAT compared with Hispanics and whites. Despite lower VAT, African-American men had similar concentrations of inflammatory biomarkers. On the other hand, African-American women had higher CRP and IL-6 than white women, and higher fibrinogen than both Hispanic and white women. After controlling for L4L5 VAT, L4L5 SAT, and age, African-American women had higher concentrations of IL-6 and fibrinogen. Stratified analyses for CRP indicated that L4L5 SAT was associated with CRP in African-American and white women after controlling for L4L5 VAT and age, but that the reverse was not true. These data indicate that African Americans had lower VAT but similar or higher concentrations of inflammatory biomarkers. African-American women consistently displayed greater inflammation compared with whites, even after controlling for VAT or SAT.

Ethnicity, energy expenditure and obesity: are the observed black/white differences meaningful?

PURPOSE OF REVIEW

Recent studies have suggested that black individuals have lower energy expenditure than whites. Many investigators hypothesized that this is why black women experience higher rates of obesity than white women. These findings initiated much research on race as a primary biological determinant of obesity and energy expenditure as a potential pathway. Race is a difficult construct to use in biomedical research.

RECENT FINDINGS

Recent findings have included: an explanation for the lower resting energy expenditure observed among black adults, data showing that relative resting energy expenditure may not be a significant predictor of weight change in African-origin populations, and inconsistent data on the role of activity energy expenditure as a determinant of children's weight change.

SUMMARY

The data suggest that black individuals have lower resting energy expenditure and possibly activity energy expenditure than white individuals. The lower resting energy expenditure is probably caused by a smaller mass of high metabolically active organs. It is unlikely that increased weight gain is associated with lower resting energy expenditure or activity among blacks, because no association has been found within populations. Clinically, it is important to focus on personal modifiable risk factors, e.g., energy intake and physical activity levels.

Effects of exercise training on resting metabolic rate in postmenopausal African American and Caucasian women

Ambiguous findings have been reported in previous studies concerning the relationships between resting metabolic rate (RMR), effects of exercise, and race in postmenopausal women. The purposes of this study were (1) to determine the effect of exercise training on RMR in postmenopausal women and (2) to determine whether this effect is different by race. We analyzed data from 24 African American (AA) (age, 56.3 +/- 5.0 years) and 23 Caucasian (CA) (age, 58.6 +/- 6.1 years) women. RMR was measured by indirect calorimetry after an overnight fast. Subjects completed tests of maximal exercise with metabolic measurements, waist to hip ratio, and body composition. At the completion of all tests, each subject was randomly assigned to either the exercise training or the control group. Aerobic exercise was performed 3 to 4 days per week for 6 months. Intensity was set at 70% to 85% maximal heart rate for 45 to 60 minutes per session. Both AA and CA exercise groups had a significant decrease (P < .05) in body weight (kilograms), percent body fat, and body mass index (BMI) and an increase in aerobic capacity, whereas the control groups did not change. There were no race effects. AA women exhibited significantly lower values than CA women for measured RMR (P < .05). The RMR (kilojoules) of the AA women (both control and exercise groups) decreased over time (P < .05), whereas the RMR of the CA women did not change. Adjusting RMR for BMI or for changes in lean body mass and fat mass did not alter these results. In conclusion, this 6-month endurance-training program did not affect RMR in these postmenopausal women, as RMR did not change in CA women, but decreased significantly over time in both groups of AA women. The factors that contribute to these findings should be the focus of future studies.

Small organs with a high metabolic rate explain lower resting energy expenditure in African American than in white adults

BACKGROUND

African Americans have a lower resting energy expenditure (REE) relative to fat-free mass (FFM) than do whites. Whether the composition of FFM at the organ-tissue level differs between African Americans and whites and, if so, whether that difference could account for differences by race in REE are unknown.

OBJECTIVE

The objectives were to quantify FFM in vivo in women and men at the organ-tissue level and to ascertain whether the mass of specific high-metabolic-rate organs and tissues differs between African Americans and whites and, if so, whether that difference can account for differences in REE.

DESIGN

The study was a cross-sectional evaluation of 64 women (n = 34 African Americans, 30 whites) and 35 men (n = 8 African Americans, 27 whites). Magnetic resonance imaging measures of liver, kidney, heart, spleen, brain, skeletal muscle, and adipose tissue and dual-energy X-ray absorptiometry measures of fat and FFM were acquired. REE was measured by using indirect calorimetry.

RESULTS

The mass of selected high-metabolic-rate organs (sum of liver, heart, spleen, kidneys, and brain) after adjustment for fat, FFM, sex, and age was significantly (P < 0.001) smaller in African Americans than in whites (3.1 and 3.4 kg, respectively; x +/- SEE difference: 0.30 +/- 0.06 kg). In a multiple regression analysis with fat, FFM, sex, age, and race as predictors of REE, the addition of the total mass rendered race nonsignificant.

CONCLUSIONS

Racial differences in REE were reduced by >50% and were no longer significant when the mass of specific high-metabolic-rate organs was considered. Differences in FFM composition may be responsible for the reported REE differences.

Physical activity in young African American women

African American women are reported to be less physically active than other population groups. This study examined personal behavioral and psychosocial and environmental factors associated with physical activity in African American women living at or below poverty. Most participants engaged in some moderate physical activity through housework and child care; 71% engaged in activity such as walking from one to seven times per week; but only 5% were vigorously active. Seventy-seven percent were active in the past, but 80% dropped out within 6 months, citing "lack of time and feeling bad" as the main reasons. Exercise self-efficacy was positively correlated with beliefs about physical and social outcomes of activity, with more active than inactive women believing that physical activity had more physical health outcomes. One-third of the women reported that family or friends disapproved of their spending time being physically active, and 45% had never been encouraged to be active by a health professional. However, health professionals' influence was positively correlated with weight reduction but not physical activity participation.

Physical activity in free-living, overweight white and black women: divergent responses by race to diet-induced weight loss

BACKGROUND

Black women are at greater risk of obesity than are white women, perhaps because of their lower levels of physical activity.

OBJECTIVE

We compared free-living activity energy expenditure (AEE) in sedentary white and black women (in overweight and normal-weight states) and in never-overweight control subjects.

DESIGN

Subjects included 46 women (23 white, 23 black) studied while overweight and after reaching a normal weight and 38 female control subjects (23 white, 15 black). Diet, without exercise training, resulted in a mean weight loss of 13 kg and a body mass index (in kg/m(2)) < 25. Body composition, sleeping energy expenditure, free-living total energy expenditure, and the energy cost of activity and aerobic capacity were assessed before and after weight loss under 4-wk, diet-controlled, weight-stable conditions and in the control subjects. AEE was defined as above-sleep energy expenditure.

RESULTS

No significant racial differences in body composition, before or after weight loss, were found. After weight loss, AEE and aerobic capacity increased in the white women and decreased in the black women (P < 0.05 and P < 0.02, respectively). After weight loss, but not before, the white women had a significantly higher mean AEE than did the black women (2448 +/- 979 and 1728 +/- 1373 kJ/d, respectively; P < 0.05), approximating AEEs in the white (2314 +/- 1105) and black (2310 +/- 1251) control subjects.

CONCLUSIONS

Relative to the responses of the white women to diet-induced weight loss, the black women became less fit and less physically active. Induction of a normal body weight in overweight black women appeared to produce a more obesity-prone state, favoring weight relapse.

Interventions to promote physical activity among African American women

The lack of routine physical activity among African American women places them at risk for negative health outcomes associated with inactivity. The number of studies focused on African American women has increased dramatically in the past decade. This review examined the intervention research literature testing strategies to increase activity among African American women. Eighteen studies with 1,623 subjects were retrieved. Diverse interventions, settings, and measures were reported. Common methodologic weaknesses included lack of randomization of subjects, single-group design, instruments without documented validity and reliability, significant attrition, and questionable timing of outcome variable measurement. Strategies to design and deliver culturally appropriate interventions are reviewed. Suggestions for future research, such as examining intragroup differences and communal resources, are provided.

Differences in resting metabolic rate between white and African-American young adults

OBJECTIVE

A reported lower resting metabolic rate (RMR) in African-American women than in white women could explain the higher prevalence of obesity in the former group. Little information is available on RMR in African-American men.

RESEARCH METHODS AND PROCEDURES

We assessed RMR by indirect calorimetry and body composition by DXA in 395 adults ages 28 to 40 years (100 African-American men, 95 white men, 94 African-American women, and 106 white women), recruited from participants in the Coronary Artery Risk Development in Young Adults (CARDIA), Birmingham, Alabama, and Oakland, California, field centers.

RESULTS

Using linear models, fat-free mass, fat mass, visceral fat, and age were significantly related to RMR, but the usual level of physical activity was not. After adjustment for these variables, mean RMR was significantly higher in whites (1665.07 +/- 10.78 kcal/d) than in African Americans (1585.05 +/- 11.02 kcal/d) by 80 +/- 16 kcal/d (p < 0.0001). The ethnic x gender interaction was not significant (p = 0.9512), indicating that the difference in RMR between African-American and white subjects was similar for men and women.

DISCUSSION

RMR is approximately 5% higher in white than in African-American participants in CARDIA. The difference was the same for men and women and for lean and obese individuals. The prevalence of obesity is not higher in African-American men than in white men. Because of these reasons, we believe that RMR differences are unlikely to be a primary explanation for why African-American women are more prone to obesity than white women.

Racial differences in insulin resistance and mid-thigh fat deposition in postmenopausal women

OBJECTIVE

To determine whether racial differences in insulin resistance between African American (AA) and white women exist in postmenopausal women and whether they are related to physical fitness and/or obesity.

RESEARCH METHODS AND PROCEDURES

We studied 35 obese AA (n = 9) and white (n = 26) women of comparable maximal oxygen consumption, obesity, and age. Total body fat was measured by DXA. Abdominal and mid-thigh low-density lean tissue (a marker of intramuscular fat) were determined with computed tomography. Glucose utilization (M) was measured during the last 30 minutes of a 3-hour hyperinsulinemic-euglycemic clamp. Insulin sensitivity was estimated from the relationship of M to the concentration of insulin during the last 30 minutes of the clamp.

RESULTS

The percentage of fat and total body fat mass were similar between AA and white women, whereas fat-free mass was higher in African American women. Visceral adipose tissue was not different between groups, but subcutaneous abdominal fat was 17% higher in the AA than in the white women. AA women had an 18% greater mid-thigh muscle area (p < 0.01) and a 34% greater mid-thigh low-density lean tissue area than the white women. Fasting glucose concentrations were not different, but fasting insulin concentrations were 29% higher in AA women. Glucose utilization was 60% lower in the AA women because of a lower non-oxidative glucose disposal. Insulin sensitivity was 46% lower in the AA women.

DISCUSSION

AA postmenopausal women have more mid-thigh intramuscular fat, lower glucose utilization, and are less insulin sensitive than white women despite comparable fitness and relative body fat levels.

Racial differences in the relation between uncoupling protein genes and resting energy expenditure

BACKGROUND

Lower resting energy expenditure (REE) in African American women may contribute to their obesity. The identification of uncoupling protein (UCP) genes has fueled a search for genes involved in energy metabolism in humans.

OBJECTIVE

We examined variation in REE in relation to variation in UCP1, UCP2, and UCP3 in 141 women aged 18-21 y.

DESIGN

Standard methods were used for REE measurements and genetic analysis. Body composition was determined with the use of dual-energy X-ray absorptiometry. Multivariate analysis was used to examine the effect of genotypes on REE and on fat mass in relation to other potentially confounding variables.

RESULTS

REE was 295 kJ/d lower in African American women than in white women. No significant variation in REE was seen for UCP1, UCP2, and UCP3 (p-55; exon 3a; and exon 3b) variants after adjustment for other variables including smoking status. For the UCP3 exon 5 variant, REE was significantly (P = 0.019) lower in African American women with the CC genotype than in those with the TT genotype. In African American women, there was a significant trend (P = 0.012) toward lower REE and a weak but nonsignificant trend (P = 0.1) toward greater fat mass across the 3 genotypes (TT, CT, and CC).

CONCLUSIONS

The significant and dose-dependent relation between lower REE and the C allele suggests that it may be a thrifty allele. The presence of this parsimonious energy metabolism in African American women, possibly linked to UCP3, may be implicated in their susceptibility to obesity. The absence of a UCP3 effect in white women is intriguing and needs to be explored to further understand possible interactions between UCP3 and other genes.

Fatty acid oxidation in African-American and Caucasian women during physical activity

The goal of this study was to determine whether differences in physical activity-related fat oxidation exist between lean and obese African-American (LAA and OAA) and lean and obese Caucasian (LC and OC) premenopausal women. Lean AA (28.4 +/- 2.8 yr, n = 7), LC (24.7 +/- 1.8 yr, n = 9), OAA (30.9 +/- 2.2 yr, n = 11), and OC (34.1 +/- 2.5 yr, n = 9) women underwent preliminary assessment of peak aerobic capacity (VO2 peak). On a subsequent testing day, participants exercised after an 8-h fast on a cycle ergometer at 15 W (approximately 40% VO2 peak) for 10 min and then for 10 min at approximately 65% VO2 peak). Fatty acid oxidation was determined using the average respiratory exchange ratio and O2 consumption during minutes 5-9 of the exercise session. Percent body fat and fat-free mass were lower (P < 0.05) in LAA (25.8 +/- 2.8% and 48.3 kg) and LC (26.4 +/- 2.0% and 45.8 +/- 1.7 kg) than in OAA (41.2 +/- 1.3% and 58.8 +/- 3.3 kg) and OC (39.3 +/- 2.7% and 58.6 kg) women. Fat oxidation among the groups was analyzed statistically using analysis of covariance with fat-free mass and VO2 peak) as covariates. During exercise at 15 W, fat oxidation was as low in LAA (0.134 +/- 0.024 g/min) as in OAA (0.144 +/- 0.026 g/min) and OC (0.156 +/- 0.020 g/min) women: all these rates of fat oxidation were lower than in LC women (0.200 +/- 0.021 g/min, P < 0.05, LC vs. all other groups). Fatty acid oxidation during higher-intensity exercise (65% VO2 peak)) was higher in LC than in OC women but was not statistically different between African-American and Caucasian groups. Fatty acid oxidation was therefore lower during low-intensity physical activity in OAA, LAA, and OC than in LC women.

Do African-American and Caucasian overweight women differ in oxygen consumption during fixed periods of exercise?

OBJECTIVE

To examine whether there are ethnic differences in oxygen consumption during fixed periods of exercise.

DESIGN

Cross-sectional.

SUBJECTS

Twenty-seven African-American and 120 Caucasian overweight adult women (body mass index=32.8+/-4.1 kg/m(2), age=36.7+/-5.6 y) prior to initiating a weight loss program.

MEASUREMENTS

Measurement of oxygen consumption occurred during four stages of a graded exercise test, with body composition assessed by dual-energy X-ray absorptiometry.

RESULTS

There were no significant differences between overweight African-American and Caucasian women for absolute oxygen consumption or oxygen consumption adjusted for either body weight or fat-free mass across four levels of a submaximal graded exercise test.

CONCLUSION

The results from this study suggest that African-American and Caucasian women do not differ in energy expenditure during fixed workloads of exercise, suggesting that this may not contribute to differences in energy balance and body weight regulation between women in these two ethnic groups.

Ethnic differences in dietary intakes, physical activity, and energy expenditure in middle-aged, premenopausal women: the Healthy Transitions Study

BACKGROUND

Menopause is a time of increased risk of obesity in women. The effect of menopause in African American women, in whom obesity is already highly prevalent, is unknown.

OBJECTIVE

We compared dietary intakes and energy expenditure (EE) between middle-aged, premenopausal African American and white women participating in a longitudinal study of the menopausal transition.

DESIGN

Dietary intakes by food record, EE by triaxial accelerometer, physical activity by self-report, and body composition by dual-energy X-ray absorptiometry were compared in 97 white and 52 African American women. Twenty-four-hour and sleeping EE were measured by whole-room indirect calorimetry in 56 women.

RESULTS

Sleeping EE (adjusted for lean and fat mass) was lower in African American than in white women (5749 +/- 155 compared with 6176 +/- 75 kJ/d; P = 0.02); however, there was no significant difference in 24-h EE between groups. Reported leisure activity over the course of a week was less in African American than in white women (556 +/- 155 compared with 1079 +/- 100 kJ/d; P = 0.02), as were the daily hours spent standing and climbing stairs. Dietary intakes of protein, fiber, calcium, magnesium, and several fatty acids were significantly less in African Americans, whereas there were no observed ethnic differences in intakes of fat or carbohydrate. Body fat within the whole group was positively correlated with total, saturated, and monounsaturated fat intakes and inversely associated with fiber and calcium intakes. Fiber was the strongest single predictor of fatness.

CONCLUSION

Ethnic differences in EE and the intake of certain nutrients may influence the effect of menopausal transition on obesity in African American women.

Comparison of risk factors for obesity in young, nonobese African-American and Caucasian women

OBJECTIVE

To determine whether specific risk factors for obesity were more evident in young, normal-weight African-American (AA) compared to Caucasian-American (CA) women.

DESIGN

Cross-sectional age-matched study.

SUBJECTS

Young, nonobese, sedentary AA (n= 13, 22.5y of age, 23.6% body fat) and CA women (n = 11, 21.5y of age, 24.0% body fat).

MEASUREMENTS

Aerobic physical fitness (peak VO2), resting metabolic rate (RMR), resting and submaximal exercise fat oxidation rates, total daily energy expenditure (TDEE) by the doubly-labeled water method, physical activity energy expenditure (PAEE), skeletal muscle glycolytic (phosphofructokinase activity (PFK)) and beta-oxidative (beta-hydroxy-acyl CoA dehydrogenase (beta-HADH)) activity, and insulin sensitivity estimated by the insulin-augmented frequently sampled intravenous glucose tolerance test.

RESULTS

The AA and CA subjects were similar in age, body mass index and body composition, but the AA women exhibited lower peak VO2. There were no group differences in RMR adjusted for body composition, or in the rates of submaximal exercise energy expenditure or fat oxidation, and no difference in skeletal muscle beta-HADH or PFK activity. The AA women exhibited lower insulin sensitivity and greater acute insulin response to glucose. The mean TDEE for the AA women was only 74% that of the CA women, primarily due to a lower physical activity energy expenditure (AA group: xPAEE = 1,246+/-438 kJ/day; CA group: x= 3,310+/-466 kJ/day.

CONCLUSION

These data indicate that PAEE and its correlates of peak aerobic capacity and insulin sensitivity are lower in young, nonobese AA women compared to their CA counterparts.

Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss

BACKGROUND

The prevalence of obesity is higher in black than in white women. Differences in energy economy and physical activity may contribute to this difference.

OBJECTIVE

The objective of this study was to compare free-living energy expenditure and physical activity in black and white women before and after weight loss.

DESIGN

Participants were 18 white and 14 black women with body mass indexes (in kg/m(2)) between 27 and 30. Diet, without exercise, was used to achieve a weight loss of >/=10 kg and a body mass index <25. After 4 wk of energy balance in overweight and normal-weight states, body composition was assessed by using a 4-compartment model, sleeping and resting energy expenditures were assessed by using a chamber calorimeter, physiologic stress of exercise and exercise economy were measured by using standardized exercise tasks, and daily energy expenditure was assessed by using doubly labeled water.

RESULTS

Weight loss averaged 12.8 kg. Sleeping and resting energy expenditures decreased in proportion to changes in body composition. Weight reduction significantly improved physiologic capacity for exercise in both groups of women, making it easier for them to be physically active. Black women had lower body composition-adjusted energy requirements than did white women-both before and after weight loss-during sleep (9% lower, 519 kJ/d; P < 0.001), at rest (14% lower, 879 kJ/d; P < 0.001), during exercise (6% lower; P < 0. 05), and as a daily total (9% lower, 862 kJ/d; P < 0.06). By contrast, free-living physical activity was similar between the groups.

CONCLUSIONS

Weight-reduced women had metabolic rates appropriate for their body sizes. Black women had lower resting and nonresting energy requirements in both overweight and normal-weight states than did white women and did not compensate with greater physical activity, potentially predisposing them to greater weight regain.

Do African Americans have lower energy expenditure than Caucasians?

OBJECTIVE

To review current studies that examine differences in energy expenditure between African Americans and Caucasians as possible modulators of attained differences in overweight status.

DESIGN

Literature review of recent clinical and laboratory studies.

METHODS

Studies chosen for review were those that examined directly resting metabolic rate (RMR), using indirect calorimetry, and total daily energy expenditure (TDEE) and physical activity energy expenditure (PAEE), using doubly labeled water.

RESULTS

Ten of 15 studies reviewed reported a lower RMR in African Americans than in Caucasians. The differences in RMR between African Americans and Caucasians ranged from 81 to 274 kcal/day and could not be explained by differences in age, fat-free mass (FFM) or methodological concerns. Two of six studies of energy expenditure using doubly labeled water suggest that Black adults have a tendency for lower TDEE that can be accounted for primarily by a lower PAEE.

CONCLUSIONS

If future studies indicate conclusively that African Americans do have lower RMR, TDEE and PAEE than Caucasians, then the disproportionally higher risk of obesity and associated metabolic disorders in Black adults may be preventable-especially in Black women. If these race differences are indeed a result of both physiological and behavioral factors, then interventions designed to reduce caloric intake and/or increase energy expenditure through lifestyle activity or structured exercise programs become especially important for African Americans and should be encouraged. International Journal of Obesity (2000)24, 4-13

Racial differences in metabolic predictors of obesity among postmenopausal women

OBJECTIVE

This study determined whether there are racial differences in resting metabolic rate (RMR), fat oxidation, and maximal oxygen consumption (VO2max) in obese [body mass index (BMI = 34+/-2 kg/m2)], postmenopausal (58+/-2 years) women.

RESEARCH METHODS AND PROCEDURES

Twenty black and 20 white women were matched for fat mass and lean mass (LM), as determined by dual energy X-ray absorptiometry. RMR and fat oxidation were measured by indirect calorimetry in the early morning after a 12-hour fast using the ventilated hood technique. VO2max was measured on a treadmill during a progressive exercise test to voluntary exhaustion.

RESULTS

RMR, adjusted for differences in LM, was 5% higher in white than black women (1566+/-27 and 1490+/-26 kcal/day, respectively; p<0.05); and fat oxidation rate was 17% higher in white than black women (87+/-4 and 72+/-3 g/day, respectively; p<0.01). VO2max (L/minute) was 150 mL per minute (8%) higher (p<0.05) in white than black women. VO2max correlated with LM in black (r=0.44, p=0.05) and white (r=0.53, p<0.05) women, but the intercept of the regression line was higher in white than black women (p<0.05), with no significant difference in slopes. In a multiple regression model including race, body weight, LM, and age, LM was the only independent predictor of RMR (r2 = 0.46, p<0.0001), whereas race was the only independent predictor of fat oxidation (r2 = 0.18, p<0.05). The best predictors of VO2max were LM (r2 = 0.22, p<0.05) and race (cumulative r2 = 0.30, p<0.05).

DISCUSSION

These results show there are racial differences in metabolic predictors of obesity. Determination of whether these ethnic differences lead to, or are an effect of, obesity status or other lifestyle factors requires further study.

Energy metabolism in African Americans: potential risk factors for obesity

BACKGROUND

Recent reports have identified a lower resting metabolic rate in African Americans than in whites, but most studies included only females and used short-term measurements with ventilated-hood systems.

OBJECTIVE

Our objective was to compare 24-h measurements of energy metabolism between African American and white women and men using a respiratory chamber.

DESIGN

Thirty-eight African American (x +/- SD: 32 +/- 7 y of age, 24 +/- 10% body fat) and 288 white (31 +/- 7 y of age, 26 +/- 12% body fat) subjects spent 24 h in a respiratory chamber for measurement of 24-h energy expenditure (24EE), sleeping metabolic rate (SMR), 24-h respiratory quotient (24RQ), and substrate oxidation rates.

RESULTS

After adjustment for sex, age, and body composition (by hydrodensitometry), African Americans had lower SMR (-301 +/- 105 kJ/d; P < 0.01) and higher 24RQ (0.014 +/- 0.004; P < 0.001) than whites, whereas 24EE was similar. A sex-specific analysis, using a subset of 38 whites with an equal sex distribution and similar age and body weight, revealed that African American women had lower SMR (-442 +/- 182 kJ/d; P < 0.05) and lower 24EE (-580 +/- 232 kJ/d; P < 0.05), but similar 24RQ values compared with white women. African American men tended to have lower SMRs than white men (-355 +/- 188 kJ/d; P = 0. 07), but had higher 24RQ values, accounting for a 992 +/- 327-kJ/d lower 24-h fat oxidation rate (P < 0.005).

CONCLUSIONS

These data not only confirm the findings of a lower metabolic rate in African American than in white women, but also suggest that fat oxidation is lower in African American men than in white men.

Changes in resting energy expenditure after weight loss in obese African American and white women

BACKGROUND

Previous studies showed that resting energy expenditure (REE) is lower in obese African American women than in obese white women. It is unknown, however, whether there are racial differences in how REE responds to weight loss and energy restriction.

OBJECTIVE

We assessed REE, body composition, and respiratory quotient before and after weight loss in obese black and white women.

DESIGN

We measured REE by indirect calorimetry and body composition by densitometry before and after 20-24 wk of treatment with a 3870-4289-kJ/d diet. Subjects were 109 obese females (24 black, 85 white) with a mean (+/-SD) body mass index (in kg/m2) of 36.3+/-5.0, weight of 95.7+/-12.6 kg, and age of 42.3+/-8.1 y.

RESULTS

Before treatment, REE, adjusted for body composition, was significantly lower in black than in white subjects (P = 0.001). Black subjects lost significantly less weight during treatment than did white subjects (13.4+/-5.9 kg or 14.2+/-5.7% compared with 16.4+/-5.6 kg or 17.0+/-5.7%, respectively; P = 0.04). Analyses that controlled for initial REE and changes in fat mass and fat-free mass showed that blacks had significantly greater decreases in REE after treatment than did whites (9.9+/-7.3% compared with 6.3+/-7.4%; P = 0.02).

CONCLUSION

This study suggests that weight loss results in greater reductions in REE in obese black women than in obese white women. These data underscore the need to consider both biological and behavioral factors when setting expectations and assessing outcomes for obesity treatment in African American women.

Effect of exercise training on long-term weight maintenance in weight-reduced men

This study investigated whether endurance training is effective for successful long-term weight maintenance after weight reduction. Fifteen male obese subjects (age, 37.3+/-5.2 years; body weight [BW], 96.2+/-13.6 kg; body mass index [BMI], 30.9+/-2.8 kg x m(-2)) participated in a 16-month exercise-intervention study. During the first 4 months, all subjects trained three to four times weekly, consuming a very-low-energy diet (VLED) during the first 2 months. After the 4-month treatment period, seven subjects continued training for 12 months (3 to 4 times per week). The other eight subjects served as a control group not involved in a training program. The regain (increase during the intervention period as a percentage of the 4-month treatment) of BW at 16 months was 64% (+/-26%) for the whole group (trained v. control, 52%+/-28% v. 74%+/-20%, P = .09). The increase in absolute fat mass (FM) was significantly lower at 16 months for the trained group (trained v. control, 4.8+/-1.9 v. 9.0+/-3.3 kg), as was the regain of FM at 16 months (trained v. control, 61%+/-24% v. 92%+/-32%, P = .05). The amount of regain of the waist circumference, waist to hip ratio (WHR), and sagittal diameter were correlated with the amount of training (hours) performed weekly (deltawaist, r = -.55, P<.05; deltaWHR, r = -.50, P = .06; deltasagittal diameter, r = -.53, P<.05). Physical fitness parameters (maximal power output [Wmax] and oxygen uptake [Vo2 max]) were significantly increased in both groups at 4 months. Trained subjects maintained high levels of physical fitness at 16 months, in contrast to the control group. In conclusion, although BW regain was not significantly different between the groups, trained subjects showed less regain of FM and higher levels of physical fitness, factors related to a lower risk for cardiovascular disease (CVD), compared with the control group. Furthermore, the regain of FM, which occurred even in the exercising group with a relatively intensive training program, suggests that maintenance of fat loss is extremely difficult.

Total daily energy expenditure in free-living older African-Americans and Caucasians

Low rates of daily energy expenditure, increased energy intake, or a combination of both contribute to obesity in African-Americans. We examined whether African-Americans have lower rates of free-living daily energy expenditure than Caucasians. One hundred sixty-four (> 55 yr) volunteers (37 African-American women, 52 Caucasian women, 28 African-American men, and 47 Caucasian men) were characterized for total daily energy expenditure, resting metabolic rate, and physical activity energy expenditure from the doubly labeled water method and indirect calorimetry. Absolute total daily energy expenditure was lower in women than men but was not different between African-Americans and Caucasians. However, we found race and gender differences in total daily energy expenditure after controlling for differences in fat-free mass. Total daily energy expenditure was 10% lower (P < 0.01) in African-Americans compared with Caucasians due to a 5% lower resting metabolic rate (P < 0.01) and 19% lower physical activity energy expenditure (P = 0.08). Moreover, total daily energy expenditure was 16% lower (P < 0.01) in women compared with men due to a 6% lower resting metabolic rate (P = 0.09) and a 37% lower physical activity energy expenditure (P = 0.06). Low rates of energy expenditure may be a predisposing factor for obesity, particularly in African-American women.

Resting metabolic rate in African-American and Caucasian girls

Recent studies have found a lower resting metabolic rate (RMR) in African-American (AA) women with obesity as compared with Caucasian (C) women with obesity. It is unknown if this difference in RMR is seen in prepubertal girls or in those of average body weight. Therefore, we studied RMR in 21 AA and 24 C girls, ages 7-10, who were well matched for age, weight, body mass index (BMI), and pubertal status. All had BMI between 15% and 85% for age and race, based on data from the First National Health and Nutrition Examination Survey. Fat free mass (FFM) was measured by dual-energy X-ray absorptiometry. RMR was measured with a Deltatrac indirect calorimeter under controlled conditions after the subjects underwent an overnight fast. The slopes of the regression equations were similar for both groups (p = 0.7). After adjustment for FEM, the AA girls had a significantly lower RMR than did the C girls (-92 +/- 32 kcal/d, p = 0.007 by analysis of covariance). This significance was maintained after exclusion of total body bone mineral content. These data suggest that normal-weight prepubertal AA girls may have reduced resting energy expenditure compared with C girls.

Resting energy expenditure in obese African American and Caucasian women

The prevalence of obesity among African American women approaches 50% and greatly exceeds rates for Caucasian women. In addition, black women lose less weight than white during obesity treatment and gain more weight when untreated. This study assessed resting energy expenditure (REE) and body composition in obese white (n = 122) and black (n = 44) women to explore the relationship between biological variables and these observed differences. REE and body composition were assessed by indirect calorimetry and densitometry, respectively, before weight loss. REE was significantly lower in black subjects (1637.6 +/- 236.9 kcal/d) than in white (1731.4 +/- 262.0) (p = 0.04). REE remained significantly lower in blacks than whites after adjusting for body weight (p = 0.02). REE, adjusted for fat-free mass, was also significantly lower in blacks than whites (p < 0.0001), although the overestimation of fat-free mass by densitometry in blacks may have contributed to this finding. There were no differences between the groups in respiratory quotient. These results suggest that a decreased REE may exist in obese black women, and it may be related to the observed differences between black and white women in the prevalence of obesity and in the response to weight loss treatment. These cross-sectional findings await confirmation in longitudinal studies.