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Assessment of Body Composition Change in a Community-Based Weight Management Program

Department of Health and Exercise Science, Appalachian State University, Boone, North Carolina (L.A.P., D.C.N.)
Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, (C.M.)
University of Colorado Health Sciences Center, Denver (J.O.H., J.R.M., H.A.), Colorado
Department of Exercise Science, University of Georgia, Athens, Georgia (K.C., D.J.S.)
Department of Physical Education and Health Promotion, The University of Wisconsin-Oshkosh, Oshkosh, Wisconsin (D.S.)
Department of Exercise Science and Sport Management, University of Tennessee, Knoxville, Tennessee (E.T.H.)

Address reprint requests to: David C. Nieman, DrPH, Department of Health and Exercise Science, Appalachian State University, Boone, NC 28608. E-mail: niemandc{at}appstate.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Objective: The purpose of this study was to validate the use of the leg-to-leg bioelectrical impedance analysis (BIA) system in assessing change in body composition over 32 weeks in overweight and obese women participating in a community weight management program.

Design: Intervention, with subjects prescribed an energy-restriction diet and exercise program for 32 weeks and body composition measured pre-study and after 12 and 32 weeks.

Subjects and Setting: Overweight and obese premenopausal women (n=201) with no overt disease were recruited at six sites into community-based weight loss programs. One hundred and twenty-four women completed all aspects of the study.

Intervention: Energy intake was set at 0.8 x resting metabolic rate (RMR) for weeks 1 through 12, 1.0 x RMR for weeks 13 through 20 and 1.2 x RMR for weeks 21 through 32. Energy intake was based on a food exchange table, with the number of food exchanges adjusted to encourage a percent distribution of 55% carbohydrate, 30% fat and 15% protein. Subjects increased their daily walking distance by 3.2 km above pre-study levels.

Measures of Outcome: Underwater weighing, seven skinfolds, and leg-to-leg BIA tests were used to assess body composition.

Results: A 3 x 3 repeated measures ANOVA revealed no significant difference in detecting change in FFM at 12 and 32 weeks among underwater weighing, BIA and skinfold, (F(4,492)=1.73, p=0.141) (decrease in FFM of 1.0±3.3 kg, 1.7±2.2 kg, and 1.4±3.3 kg respectively, 32 weeks).

Conclusions: The leg-to-leg BIA system provides a valid measure of body composition change in overweight premenopausal women during a 32-week community-based weight loss program.

Key words: fat-free mass, bioelectrical impedance, underwater weighing, skinfolds, diet

	INTRODUCTION

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Bioelectrical impedance analysis (BIA) was developed in the 1960s and has emerged as one of the most popular methods for estimating relative body fat [1–3]. BIA is relatively simple, quick, portable and noninvasive and is currently used in diverse settings, including private clinicians’ offices, wellness centers and hospitals.

When the appropriate BIA equation is used and the sources of measurement error are controlled, estimation of fat-free mass (FFM) and relative body fat through the BIA method has been found to have about the same accuracy as the skinfold method in a diverse group [1,3–5]. The standard error of estimate (SEE) or prediction error for skinfold measurement is about 3.3% body fat and about 3.5% for BIA [3]. The BIA method, however, is preferable in some settings to the skinfold method because it does not require a high degree of technician skill and is more comfortable and less intrusive. There is still debate over whether or not BIA accurately predicts changes in body composition during a weight loss program [4]. Published studies are mixed, with some supporting the accuracy of BIA in detecting FFM and body composition changes [6–8], while others claim there is substantial over- or under-estimation when compared to the underwater weighing method [9–14].

Recent attention has been given to the leg-to-leg BIA system that has several operational advantages when compared to the conventional arm-to-leg approach [15,16]. Nuñez et al. [15] have provided data on a single frequency 50 kHz leg-to-leg BIA system combined with a digital scale that uses stainless steel pressure-contact foot pad electrodes. This leg-to-leg BIA system is functionally different from other BIA systems that require the use of arm and leg electrodes and separate measurement of body weight. The leg-to-leg BIA system provides impedance measurements and body composition estimates that are comparable to the arm-to-leg system, while offering the advantage of increased speed and ease of measurement. Equations currently used in the leg-to-leg BIA system have been generalized to allow FFM estimates from adults varying widely in body composition and age [16]. In a study of 98 moderately obese females and 27 non-obese controls, Utter et al. [16] reported no difference between underwater weighing and BIA in estimating FFM.

Current weight loss guidelines from the National Heart, Lung and Blood Institute (NHLBI) recommend a daily energy deficit of 300–1000 kilocalories to achieve body mass reductions of 0.5 to 2.0 pounds (0.23 to 0.9 kilograms) per week [17]. The initial goal is to achieve a 10% body mass loss within six months. These guidelines can be accomplished through a community-based weight loss program that uses the food exchange system to monitor energy and nutrient intake [18]. The leg-to-leg BIA system could serve as a convenient method for measuring body composition change within this setting. However, there are limited data indicating that the leg-to-leg BIA system is a valid tool for measuring body composition change during a long-term community-based weight loss program.

The purpose of this study was to validate the use of the leg-to-leg BIA system in assessing change in body composition over 32 weeks relative to underwater weighing and skinfolds in a large group of overweight and obese women participating in a community-based weight management program.

	MATERIALS AND METHODS

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Subjects and Research Design
Overweight and obese premenopausal women (n=201) with no overt disease were recruited into weight management programs at six university sites: Appalachian State University-Boone, North Carolina, University of Tennessee-Knoxville, University of Wisconsin-Oshkosh, University of Georgia-Athens, Colorado State University-Fort Collins and University of Colorado Health Sciences Center-Denver. Subjects were recruited according to these selection criteria obtained from a pre-study medical history questionnaire: 1) between the ages of 22 and 55 years and pre-menopausal, 2) non-smoker, 3) in good health and with no known diseases including cancer, diabetes and coronary heart disease, 4) a body mass index (BMI) between 25 and 55 kg/m², 5) not currently on a weight loss diet and weight stable within 4% of body weight over the past year, 6) fewer than 30 minutes of moderate-to-vigorous exercise a day and 7) not experiencing any pain that would interfere with full participation. Ethnicity was not recorded, and generalized population formulas were used in estimating the body composition for all subjects.

All subjects were prescribed an energy-restriction diet and exercise program for 32 weeks, with body composition and nutrient intake measured pre-study, after week 12 and after week 32.

Energy-Restriction Diet
Each subject’s resting metabolic rate (RMR) was estimated using the revised Harris-Benedict equation to determine her energy intake during the 32-week diet [19]. Energy intake was set at 0.8 x RMR for weeks 1 through 12, 1.0 x RMR for weeks 13 through 20, and 1.2 x RMR for weeks 21 through 32. Energy intake was based on a food exchange table, with the number of food exchanges adjusted to encourage a percent energy intake of 55% carbohydrate, 30% fat and 15% protein intake [18]. Subjects attended 22 one-hour sessions with the project dietitian and research staff to ensure compliance with the diet and exercise program. Dietary compliance was measured in two ways: 1) a food exchange checklist which was filled in each day and given to the project dietitian every one to two weeks for review, 2) three-day food diaries kept at pre-study, week 12, and week 32.

Measurement of Energy and Nutrient Intake
Each subject was instructed on how to record food intake in the three-day diary by the project dietitian using food models and household measures [20]. Nutrient intake from the three-day food records was assessed by using a computerized dietary analysis system, the Food Processor Plus, Version 7.0 (ESHA Research, Salem, OR).

Exercise Program
Prior to the study, subjects wore the SW-701 Pedometer (ACCUSPLIT, Inc., Silicon Valley, CA) for five consecutive days to establish a mean daily walking distance. Subjects wore the pedometer every day of the 32-week study and daily distance was recorded in an exercise log and turned in every one to two weeks to the research staff. Subjects were asked to increase their daily walking distance by 3.2 km above pre-study levels.

Body Composition
Subjects’ body mass and stature were determined with a physician’s balance beam scale and stadiometer, respectively. Underwater weighing, skinfolds and leg-to-leg BIA tests were used to assess body composition [21]. Prior to each body composition testing appointment, subjects were instructed to adhere to the following guidelines to maintain normal hydration [3]: 1) nine to twelve hours fasted, 2) abstinence from caffeine and alcohol for 24 and 48 hours, respectively, 3) avoidance of exercise for 12 hours and 4) avoidance of diuretic medications within seven days of the test. A questionnaire filled in at the time of body composition testing verified that subjects followed these instructions.

During underwater weighing, subjects were asked to expel as much air as possible from the lungs at complete submersion. After several trials the highest underwater weight that could be repeated was recorded. Body density was determined by using the Goldman and Buskirk equation [22]. The subjects’ residual volume was measured by the nitrogen washout technique with subjects seated out of the water [23]. Percent body fat and FFM were derived from body mass and body density values using the equation of Brozek et al. [24].

Skinfold measurements were taken at seven sites: chest, triceps, subscapular, midaxillary, suprailiac, abdominal and thigh using Lange skinfold calipers (Beta Technology, Inc., Cambridge, MD). Skinfold thickness was measured to the nearest 0.5mm on the right side of the subjects in compliance with the Anthropometric Standardization Reference Manual protocol [25]. The mean of two measurements that were within 10% agreement were used for analysis. The sum of seven sites was used to calculate body density using the equation of Jackson and Pollock [26]. Percent body fat and FFM were derived from body mass and body density values using the equation of Brozek et al. [24].

BIA measurements were taken using the Tanita Body Fat Analyzer (Model TBF 105, Tanita Corporation of America, Inc., Arlington Heights, IL) [15,16]. Subjects were measured by standing erect, with bare feet on the footpads and in minimal clothing (undergarments or swimsuits). The analyzer’s four electrode footpads are stainless steel and are connected to the top of a platform scale. Each footpad is divided in half to allow anterior and posterior portions to form two separate electrodes. Body mass and leg-to-leg impedance are measured simultaneously when the subject steps onto the footpads. Current is activated through the anterior portion of footpad electrodes, and the voltage drop across the posterior electrodes is then measured [15]. FFM and body density were calculated using prediction equations supplied by the manufacturer (using weight, age and an impedance index, height²/Z). Body fat percentage was estimated using the equation of Brozek et al. [24].

Statistical Analyses
A 3 (body composition methods) x 3 (time points at pre-study, 12 weeks and 32 weeks) repeated measures ANOVA was used to test body composition estimates by the three different methods over time. When the group x time interaction p value was ±0.05, differences between methods were assessed using paired t tests adjusted for multiple comparisons. Paired t tests and Pearson r values were calculated to test simple correlations in estimating FFM between BIA, skinfolds and underwater weighing. The difference in FFM between underwater weighing and BIA was plotted against mean FFM to explore systematic differences as suggested by Altman and Bland [27]. Statistical significance was set at the p0.05 level and values expressed as mean ±SD. The data were analyzed using the Statistical Package for the Social Sciences (SPSS/PC+) software program (SPSS, Chicago, IL).

	RESULTS

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Subject characteristics are summarized in Table 1. Estimated RMR prior to study was 1,609±142 kcal/day, 1,533±156 kcal/day at 12 weeks and 1,517±156 kcal/day at 32 weeks. Energy intake fell 37% during the first 12 weeks to a level that was slightly above the goal of 0.8 x RMR or 1,287 kcal/day (Table 2). Energy intake was 32% below pre-study by week 32, which was 340 kcal/day below the goal of 1.2 x RMR or 1,820 kcal/day. Walking distance during the first 12 weeks increased by an average of 20.7±11.1 km/wk above pre-study levels, slightly under the goal of an increase of 22.5 km/wk (Table 2). Walking distance increased an average of 15.8±7.5 km/wk above pre-study levels during the last 20 weeks.

View larger version (29K): [in this window] [in a new window]   Fig. 1. Bland-Altman plot of the difference between FFM measured by underwater weighing and BIA compared to the average FFM by the two methods.

	DISCUSSION

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The cross-sectional pre-study data from the overweight and obese premenopausal female subjects showed that the leg-to-leg BIA system accurately assessed FFM relative to underwater weighing for the groups as a whole. Estimates of FFM from these two methods were significantly correlated (r=0.81) with an SEE of 4.5 kg, which are acceptable given the multiple sites from which data were collected nationwide. We have previously reported a smaller SEE (3.7 kg) in the estimation of FFM through the Tanita BIA method in women measured in one laboratory [16]. The mean difference in estimation of FFM between BIA and underwater weighing in the 201 subjects at baseline was 0.3 kg, substantially less than the 2.5 kg between skinfolds and underwater weighing. BIA, however, did systematically underestimate FFM in subjects with a higher FFM and overestimated FFM in subjects with a lower FFM. Subjects lost an average of 7.9 kg during the 32-week, community-based, weight-loss program, with FFM accounting for 13% of this change. Change in FFM was detected equally well among underwater weighing, BIA and skinfolds.

The validity of the conventional arm-to-leg BIA system in assessing body composition in obese individuals (cross-sectionally) has been questioned [1,3,5,10,12–14]. Most researchers have reported that equations used in arm-to-leg BIA systems overestimate FFM in obese subjects when compared to reference methods [12–14,28–30]. Various fat-specific or generalized equations have been developed and recommended for the testing of obese subjects [5,31,32]. Equations currently used in the leg-to-leg BIA system (Tanita Body Fat Analyzers) have been generalized to allow FFM estimates from female adults varying widely in body composition and age. Our data indicate that the leg-to-leg BIA system assesses FFM in a group of overweight and obese premenopausal women with a fair degree of accuracy when measured in diverse settings and when following the guidelines described in the methods, although estimates are less valid in obese women with unusually high or low levels of FFM.

Decreases in FFM over 32-weeks in the premenopausal females participating in the six community-based weight loss programs were accurately detected by the leg-to-leg BIA system and skinfolds relative to underwater weighing. These data are consistent with those of Utter et al. [16] who reported that the leg-to-leg BIA system accurately assessed changes in body composition among 98 moderately obese women through diet alone or when combined with exercise during a 12-week study. There are conflicting reports regarding the validity of the conventional arm-to-leg BIA system in predicting changes in the body composition of obese women. Using a four-component model as a criterion measure, Evans et al. [6] showed that BIA and skinfold methods accurately estimated body composition change in 27 obese women induced by diet and exercise interventions over a 16-week period. Kushner et al. [8] also found that the arm-to-leg BIA system was valid for measuring changes in FFM in obese women. Vazquez et al. [11], however, concluded that all eight BIA equations investigated overestimated losses of FFM in obese women during very-low-energy diets. Other investigators have reported that BIA systematically underestimated loss of FFM during weight loss [9,10]. In many weight loss investigations, the change in body composition and FFM is relatively small (<3 kg), limiting the ability of BIA to detect changes and thus accounting for the lack of consensus among studies [6,16].

In summary, the leg-to-leg BIA system used in this community-based weight management program provided quick and easy-to-obtain body composition measurements in overweight and obese premenopausal women. When compared to underwater weighing, the leg-to-leg BIA system provided an accurate assessment of body composition change over 32 weeks.

	ACKNOWLEDGMENTS

 
This study was supported, in part, by an unrestricted educational grant from Abbott Laboratories, Morgan Hill, CA.

Received June 21, 2000. Accepted September 22, 2000.

	REFERENCES

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