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ORIGINAL RESEARCH COMMUNICATION |
1 From the Division of Physiology and Metabolism, Departments of Human Studies and Nutrition Sciences, University of Alabama at Birmingham.
2 Supported by NIH grants R01 DK 49779-01 and R01 DK51684-01, General Clinical Research Center grant M01-RR00032, Clinical Nutritional Research Unit grant P30-DK56336, and a University of Alabama at Birmingham University-Wide Clinical Nutrition Research Center grant. Stouffer's Lean Cuisine entrées were provided by the Nestlé Food Co (Solon, OH), and Weight Watcher's Smart Ones were provided by the Heinz Frozen Food Co (Pittsburgh).
3 Address reprint requests to GR Hunter, Room 205, Education Building, 901 South 13th Street, University of Alabama at Birmingham, Birmingham, Alabama 35294-1250. E-mail: ghunter{at}uab.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Objective: We compared objectively assessed total energy expenditure (TEE) with estimates of energy expenditure (EE) from self-reported physical activity (PA) in overweight black and white women before and after weight loss. We also compared those values with values in never-overweight control subjects.
Design: A total of 20 white and 21 black premenopausal women were evaluated while overweight and weight reduced; 20 white and 14 black control subjects (matched with women in the weight-reduced state) were evaluated once. Weight loss of 
10 kg was achieved by energy restriction in the overweight subjects. The evaluations were as follows: body composition (dual-energy X-ray absorptiometry), free-living TEE (doubly labeled water), Tecumseh Occupational Activity Questionnaire, Minnesota Leisure Time PA Questionnaire, and Baecke Activity Questionnaire.
Results: Questionnaire estimates of TEE were overestimated when compared with TEE (P < 0.001). Overweight women overestimated TEE 49% more than did never-overweight control subjects. After weight loss, white women reduced overestimation of EE 48% (P < 0.05), so that their overestimation of EE was not different from that of black and white control subjects. Black women overestimated to the same extent both before and after weight loss.
Conclusions: Premenopausal women overestimate PA estimates on questionnaires. Overestimation of PA in weight-reduced black women is greater than in weight-reduced white women and never-overweight black and white women.
Key Words: Weight loss • self-reported physical activity • energy expenditure • physical activity questionnaires • overestimation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Weight loss tends to have different effects on the energy expenditure (EE) of obese black and white women (2, 5). Foster et al (5) found that weight loss resulted in greater reductions in resting EE in obese black women than in obese white women. Also, we have previously shown that activity-related EE (AEE) and aerobic capacity increased in white women but decreased in black women after diet-induced weight loss and that the mean AEE in white women was significantly higher than in black women, but only after weight loss (2). In the same study, it was found that black women who lost weight showed a significant decrease in aerobic capacity when adjusted for fat-free mass (FFM), as well as a decrease in energy-cost of activity. However, after adjusting for FFM, white women showed increases in both aerobic capacity and AEE (2). A 1-y follow-up of this group found that weight-reduced black women regained more weight than did their white counterparts (14). Such findings bring us closer to understanding why weight maintenance is often a greater challenge for black women.
PA reported on questionnaires can be used to make an indirect measurement of EE, which is based on a person's perception of his or her own quantity of PA. Most validations of PA questionnaires indicate that persons tend to overestimate PA. Some studies have shown that reporting of PA is less accurate in overweight persons (15) and that overestimation is greater with older age and higher body fatness (16). Little is known about why people overestimate PA or whether sex, ethnicity, fitness level, or other factors could predispose a person to overestimate PA. An understanding of the factors that influence overestimation of PA could be important for understanding why people choose to be active or inactive. Therefore, the objective of this study was to compare objectively assessed TEE with estimates of EE from self-reported PA in overweight black and white women before and after weight loss and with never-overweight control subjects.
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SUBJECTS AND METHODS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Study design
Subjects were evaluated in the overweight state, reassessed in the weight-reduced state, and compared with never-overweight control subjects. Initially, they were maintained in weight stabilization for 4 wk through dietary control. During this time their body weights were measured 3–5 times weekly at the General Clinical Research Center (GCRC), and at the end of the 4 wk they were admitted to the GCRC for a 4-d evaluation. Admission was timed to be during the follicular phase of the menstrual cycle. A macronutrient-controlled diet was provided during the final 2 wk of weight maintenance. The energy content was appropriately adjusted to ensure a stable body weight (<1% variation from the subjects' weight at the beginning of the 4 wk), and the diet consisted of 20–23% of energy from fat, 20–23% from protein, and 56–59% from carbohydrate. After discharge, the GCRC provided all meals for the period of weight reduction. Subjects were provided a 3350-kJ (800-kcal) diet, which was designed to meet all nutrient requirements excluding energy requirements. Stouffer's Lean Cuisine entrées (Nestlé Food Co, Solon, OH) were provided for lunch and dinner, and alcohol intake was not permitted during the study. Subjects were maintained on the diet until 10 kg in body weight was lost and a BMI < 25 was achieved. There was no intervention to alter subjects' self-selected PA patterns. Having attained a normal body weight, subjects then repeated the 4-wk protocol of energy balance followed by the 4-d admission and evaluation at the GCRC. The never-overweight control subjects also underwent this 4-wk protocol and assessment at the GCRC.
Body composition
Fat mass (FM), FFM, and percentage of body fat were determined by dual-energy X-ray absorptiometry (adult software, version 1.5g, DPX-L; Lunar Radiation Corp, Madison, WI) in the Department of Nutrition Sciences at the University of Alabama at Birmingham. Subjects were scanned in light clothing while lying flat on their backs with their arms by their sides. All scans were analyzed by the same investigator.
Doubly labeled water
TEE was determined in the overweight and weight-reduced states with use of the doubly labeled water (DLW) technique. A baseline urine sample (10 mL) was collected, and a mixed dose of DLW was administered orally during weight stabilization, on the morning 2 wk before GCRC admission. The isotope loading dose was 
0.10 g 18O and 0.08 g 2H/kg body mass. The average initial isotope enrichment of 2 urine samples was obtained the morning after dosing and on the 14th day; 2 additional final samples were obtained, and results were averaged. The off-line zinc-reduction method (19) and the equilibrium technique (20) were used to analyze all urine samples in triplicate for 2H and 18O, respectively. TEE was then calculated with use of equation 12 of de Weir (21), and a food quotient of 0.88 was based on the foods provided.
Physical activity questionnaires
QEE (estimated EE from self-reported PA) was determined with use of questionnaires. The TEC Questionnaire (17), the MNLTPA Questionnaire (18), and the Baecke Activity Questionnaire (22) were administered to subjects during their baseline and weight-reduced visits. The TEC has 4 sections that assess work history (hours worked per week per job), transportation to and from work, PA at work, and flights of stairs climbed at work. The MNLTPA is a list of 63 leisure-time activities, grouped into 10 categories. Subjects recorded the duration and frequency of the activities they did during the past 12 mo.
We used an average duration for sleep of 8 h/d and for meals of 3 h/d and combined the TEC and MNLTPA to calculate EE (QEE) (17). The TEC and MNLTPA are both 1-y quantitative history instruments that can be used together (17, 23), because they each measure separate aspects of PA. Both questionnaires were scored together according to instructions in Montoye et al (17). This scoring provided a mean activity metabolic index value per day. This value multiplied by the subject's body weight gave an estimation of TEE in kilocalories per day. These self-administered questionnaires were previously validated in white women aged 20–60 y against Caltrac activity counts [TEC, r = 0.34 (24); MNLTPA, r = 0.22 (24)]. Although used in several different studies (25, 26), to our knowledge the MNLPTA and TEC have not been validated for black persons. We did a correlation between the TEE measured from DLW and the sum of the TEC and MNLPTA estimated TEE separately for the black and white subjects (weight-reduced and control subjects combined). The TEC and MNLPTA correlated very similarly in the 2 races (both r = 0.40, P < 0.05). These correlations compare favorably with those previously reported for the 2 instruments (24, 27).
With use of the Baecke questionnaire, activity indexes were calculated for 3 components: work, sport, and leisure, with use of a 5-point scale from 1 (never) to 5 (always) for each activity. These activity indexes indicated the levels of habitual PA for each subject. The Baecke questionnaire has been validated previously (22, 28).
Socioeconomic factors were not assessed or considered in the selection process. However, the TEC questionnaire requests the person's job title. On the basis of job title alone, each subject was categorized into a specific social class according to the Registar General's classification of social class in the United Kingdom (29). This method has 5 categories, numbered 1 (professional) to 5 (unskilled). Most of the women were recruited from the university campus area, and none of the subjects were categorized as unskilled. The subjects in classes 1 and 2 were grouped together as professional and the remainder were classed as nonprofessional (classes 3 and 4). Classification of socioeconomic status found that 53% of white women and 50% of black women were professionals, and the remaining subjects were nonprofessionals.
Exercise testing
Maximal oxygen uptake (
O2max) was measured during a maximal modified Bruce graded treadmill protocol (30). The 3 criteria for achievement of O2max were 1) a leveling or plateauing of O2max, 2) a peak respiratory ratio > 1.1, and 3) a maximum heart rate within 10 beats of the age-predicted maximum. All subjects reached at least 2 criteria for achieving O2max. Oxygen consumption and carbon dioxide production were measured continuously by an open circuit spirometer and then analyzed by a metabolic cart (model 2900; Sensor Medics, Yorba Linda, CA).
Biceps and quadriceps strength were measured by isometric elbow and knee extension tests (31). Forces were measured with a universal shear beam load cell (LCC 500; Omega Engineering, Stamford, CT). To limit shoulder movement during the elbow flexion test, subjects were required to wear a harness and stand with their arms fixed to the side. Force was measured on the right forearm at the level of the styloid process. During the knee extension test, the subjects were required to sit with their legs and upper torso strapped to a chair to prevent hip movement. The force was measured at the ankle. After 3 practice trials, 3 maximal isometric contractions were recorded with 60-s rest between each trial.
Statistics
The t test was used to evaluate potential racial differences for descriptive variables. Two (before and after weight loss)-by-two (race) analysis of variance (ANOVA) with repeated measures on weight loss was used to evaluate estimates of EE and fitness for the overweight women. Two (group)-by-two (race) ANOVA was used to evaluate differences between the weight-reduced women and the never-overweight control subjects for all variables. Scheffe post hoc analysis was used to determine whether there were significant differences between the overweight and weight-reduced states for overestimation of EE, strength, and O2max. Overestimation was the difference between QEE and TEE in kilocalories per day. Pearson product correlations were run between TEE and QEE and between overestimation of EE and selected body-composition variables. The level of significance was set at P < 0.05. Data were missing for some variables for various reasons that included equipment malfunction, subject illness, and experimental error. Therefore, subject numbers differ between some variables.
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RESULTS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. No significant differences were found between black and white women in age, weight, or body composition before or after weight loss. The time taken for subjects to achieve a weight loss of >10 kg and a BMI < 25 was not significantly different between black and white subjects. The average weight loss was 16% of baseline weight, resulting in a significant decrease in BMI, BF, and FFM in both racial groups (all P < 0.001). There were no racial differences in the losses of FM and FFM. Small but significant differences in both BMI and percentage of body fat were found between black and white control subjects (P < 0.05).
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). The correlation between TEE and estimated EE from the QEE when run for the black and white women separately was r = 0.40 (P = 0.05) and was the same for both races. Estimation of EE from QEE significantly decreased (P < 0.001), but there was no significant race effect (P = 0.435). There was a significant interaction effect (P = 0.041).
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). Baecke self-reported PA scores increased significantly with weight loss (P = 0.006), with blacks reporting higher PA than did whites (P = 0.027) (Table 2
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). However, a significant weight loss-by-race interaction (P = 0.006) and post hoc analysis indicated that black weight-reduced women overestimated more than did control subjects (combined black and white), but white weight-reduced women did not overestimate EE differently from control subjects. There were no racial differences in overestimation of EE in control subjects. The overweight women (before weight loss) overestimated their EE significantly more than did the control subjects (overweight subjects: 869 ± 388 and 981 ± 284 kcal/d in whites and blacks, respectively; control subjects: 670 ± 365 and 551 ± 375 kcal/d in whites and blacks, respectively; P < 0.05), and this overestimation was not affected by race. No significant differences were found between the weight-reduced women and the control subjects in self-reported PA with the use of the Baecke questionnaire. However, there was a significant group-by-race interaction (P < 0.004).
A positive correlation was found between percentage of body fat (r = 0.39, P < 0.05) and FM (r = 0.46, P < 0.02) with overestimation of EE in the overweight women, but not in the normal-weight women (both weight-reduced and control subjects). FFM and body weight were not significantly related to overestimation of EE in any group.
Aerobic fitness and strength
The time-by-race interaction and post hoc evaluation showed a significant decrease in absolute aerobic capacity (mL O2/min) in the black women, but no significant change in the white women (Table 2). When aerobic capacity was expressed relative to body weight, O2max significantly increased with weight loss (P < 0.05). Black women had significantly lower O2max than did white women, and the time-by-race interaction was significant. Post hoc tests showed that white women had increased O2max with weight loss, whereas O2max in the black women did not change (Table 2). ANOVA analysis of O2max between black and white weight-reduced and never-overweight control subjects showed only a significant race effect, with white women having a higher O2max whether expressed in absolute terms or relative terms.
Both elbow flexion and knee extension strength decreased with weight loss (Table 2). A significant interaction between weight loss and race for knee extension strength, with subsequent post hoc tests, showed that black women lost significant elbow flexion and knee extension strength (P < 0.05), but white women did not. ANOVA comparisons between weight-reduced and never-overweight control subjects showed that never-overweight control subjects were stronger than were weight-reduced women (Table 2). To determine whether fitness changes were associated with changes or lack of changes in estimated EE on the QEE, correlations were run between overweight to post-overweight changes in O2max and knee extension strength and changes in QEE. Knee extension strength was significantly related to QEE (r = –0.41, P < 0.04), suggesting that subjects who maintained strength tended to overestimate estimates of EE less after weight loss.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The reason for this racially divergent response to weight loss is unknown. Other studies have reported racial differences in physiologic responses to weight loss (2, 3, 5). Weinsier et al (2) found that activity EE and aerobic capacity increased in white women and decreased in black women after weight loss, suggesting that overweight black women become less fit and less physically active when reduced to a normal body weight. It was also shown that black women expend less energy than do white women matched for FFM and FM because they have lower resting and nonresting energy requirements in both the overweight and normal-weight states (3). Another study investigating weight loss in obese black and white women found that under the same dietary treatment black women lost significantly less weight and showed a greater reduction in resting EE than did white women (5). It could be that these physiologic changes that occur with weight loss influence a person's perception of PA.
Consistent with this hypothesis, the black overweight women in this study showed a decrease in strength and O2max after weight loss, whereas the white women did not, suggesting that the white women were better adjusted physiologically to the loss of 13.5 kg than the black women were to the smaller weight loss of 12.5 kg. It is possible that, because white women did not experience a reduction in physical fitness with weight loss, PA became easier at a lower body weight, causing an associated reduction in perceived exertion. In contrast, the reduction in fitness experienced by black women resulted in maintenance of pre-weight-loss levels of perceived exertion. The significant negative relation between change in knee extension strength and change in QEE estimates of EE further support this possibility. Women who maintained strength with weight loss might detect less difficulty in moving their reduced weight and, therefore, might not overestimate PA as much as women who lose leg strength.
Cultural and psychosocial factors were not considered in the selection process for this study, and it is possible that they could be confounders in the association between race and overestimation of EE. However, the women were categorized into social classes according to their job title. The findings that 53% of white subjects and 50% of black subjects were professionals (social class 1 and 2) and that the remaining subjects were nonprofessionals suggest that occupation, at least, may not have influenced the results of this study. Some studies have shown that social factors such as environment, policy, and culture have an influence on PA (32–34). Psychosocial characteristics, such as poor awareness and memory of the PA duration, and subconscious biasing toward a level of PA that is perceived to be appropriate, could have caused some subjects to overestimate their EE.
Several other studies indicate that, in comparison with white women, black women are less preoccupied with dieting and are more tolerant of being overweight and that their social environment is less negative about being overweight (35–40). Therefore, it could be that white women are more conscious about weight loss and pay more attention to their participation in PA, whereas black women are less concerned and make more discrepancies in reporting PA accurately. Despite the lack of data on psychosocial factors in this study, it must be acknowledged that there was similar overestimation of EE between the never-overweight black and white women and between the overweight black and white women. This similarity suggests that the questionnaire responses could be unbiased, with the ethnic difference in overestimation being specific to the weight-reduced state.
BMI and percentage of body fat were found to be significantly higher in white control subjects than in black control subjects, but the differences were very small and are unlikely to have a significant effect. The number of successfully completed questionnaires was a limitation in this study. Although the questionnaires used were previously well validated, this study identifies the limitations of self-reporting. In research, inaccurate reporting can have serious implications for the interpretation of weight-loss intervention outcomes. Results from this study also point out that weight-loss programs may not be equally effective among different racial groups. Because exercise is an important component for successful weight loss and weight-loss maintenance, particularly for black women, it will be critical to develop more accurate methods for assessing PA in future ethnically mixed studies.
In summary, the findings of this study suggest that the observed differences in self-reported PA after weight loss in previously overweight black and white women could be partly attributed to different physiologic responses to diet-induced weight loss. This finding is in direct contrast with the similar self-reporting of PA among black and white never-overweight control subjects. The women in this study may not be truly representative of all black and white American women, but the current data do highlight the importance of considering cultural and physiologic differences when assessing PA in women after weight loss.
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ACKNOWLEDGMENTS |
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All authors had significant input into the analysis and interpretation of data and into the writing of the manuscript. None of the authors had any financial or personal interests, including advisory board affiliations, in any company or organization sponsoring the research.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
) and black (•) women. Two (weight loss)-by-two (race) repeated-measures ANOVA was used to compare the effects of weight loss on overestimation of EE in black and white women (weight loss effect: P = 0.076; race effect: P = 0.023; and weight loss x race interaction: P < 0.038). Two (group)-by-two (race) univariate ANOVA was used to evaluate the difference in overestimation of EE between control black and white women (group: P = 0.310; race: P = 0.63; interaction: P < 0.006).