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Keywords:

  • body adiposity index;
  • body fat;
  • women

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Objective

This study aimed to verify the validity of BAI in predicting %BF in a sample of Brazilian women

Design and Methods

A total of 102 women (average age 60.3 ± 9.8) were assessed. To determine percentage body fat (% BF), dual-energy X-ray absorptiometry (DXA) was used as the “gold standard.” To evaluate the association between body adiposity index (BAI) and % BF assessed by DXA, we used Pearson's correlation coefficient. Paired sample t-test was used to test differences in mean % BF between BAI and DXA. To evaluate the concordance between % BF measured by DXA and estimated by BAI, we used the Lin's concordance correlation coefficient and the agreement analysis of Bland-Altman.

Results

The correlation between % BF obtained by DXA and that estimated by BAI was r = 0.65, P < 0.001. Paired t-test showed significant mean difference between methods (P < 0.0001). Lin's concordance correlation coefficient was C_b = 0.73, which is classified as poor, while the Bland-Altman plots showed BAI underestimating % BF in relation to the used criterion measure in a large portion of the sample.

Conclusions

Results of the present study show that BAI presented low agreement with % BF measured by DXA, which is not recommended for % BF prediction in this studied sample.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Anthropometric methods of body composition assessment using weight measurements, height and body circumferences [1] have been used as an alternative to laboratory methods, which are costly and require sophisticated equipment and skilled professionals, making them impractical for evaluating large population groups [2]. Anthropometric methods are practical, quick and inexpensive and can be easily applied to large samples [3]. However, despite showing an association with body fat, they do not allow the breakdown of the constituent elements of body composition [4].

Because of this limitation, a new index [5] was recently proposed based on measurements of height and hip circumference for estimating body fat in a simple and easy way. This index, called body adiposity index (BAI), was developed with data from Mexican American adults of both sexes, from 18 to 67 years old and tested in an African American sample. The method proved to be valid for estimating percentage body fat (% BF) in these populations, representing an evolution in anthropometric methods using simple height and hip circumference measures to estimate body composition does a two-compartment segmentation of the body in fat mass and fat free mass.

BAI has been analyzed in comparison with other methods and as to its validity in determining % BF. Some studies have indicated that BAI is not a more accurate measure of adiposity than is body mass index (BMI) [6-10], waist circumference, or hip circumference [11, 12], as was also observed that the BAI was a better predictor of adiposity than BMI [13-15].

In relation to the analysis of % BF determined by BAI, the comparison a group of women with familial partial lipodystrophy and healthy women with the same age and BMI, lipodystrophic women had significant differences in fat content and distribution as evaluated by dual-energy X-ray absorptiometry (DXA), and BAI was able to catch differences in the total of body fat content between groups, as well as DXA [14]. Was also found that BAI estimates % BF with high accuracy in nondialyzed chronic kidney disease patients [16]. Opposite results shown that BAI does not provide valid estimates of % BF for a Caucasian, European population [17], European American adults [15] and in athletic women [18], determining that this method should not be used for predicting individual % BF.

Although some studies verify the validity of the BAI, was observed great lack of standardization in the criteria used by the studies, as well as controversial results. The authors [5] considered that the results of the BAI could be extrapolated to other populations in Central and South America; however, they suggested further research was needed to validate and confirm the results.

Thus, this study aimed to verify the validity of BAI in predicting % BF in a sample of Brazilian women, using dual-energy X-ray absorptiometry (DXA) as the reference method.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

This was a cross-sectional analytical study carried out on 102 women with a mean age of 60.3 ± 9.8 ranging from 35 to 83 years old. They participated in an exercise project open to the public of a federal university in Brazil, and the baseline data was used in this study. With regard to skin color, the study included whites, intermediates and blacks. However, because of high individual ancestral variability, Brazilian's have a singular proportion of Amerindian, European and African ancestries in their genome, and cannot predict ethnic group of persons from their skin color [19].

The project was approved by the Ethics Committee for Research of Viçosa Federal University, Minas Gerais State, Brazil, and informed written consent was obtained from all participants.

Anthropometric data

The hip circumference measurement was taken at the point of the largest circumference of the buttocks, with a flexible tape, with a precision of 0.1 cm. Body height was measured to the nearest 0.5 cm and weight was measured in individuals wearing light clothes to the nearest 0.1 kg on a balance beam scale. The mean of the three measures were recorded. All measurements were performed at the Human Performance Laboratory at the Federal University of Viçosa.

With these anthropometric measurements, BMI and BAI were calculated by the following equations: BMI = weight (kg)/height2 (m), BAI = (hip circumference (cm)/height (m)1.5) − 18.

Body composition by DXA

Measurements of total body composition were determined by the dual-energy X-ray absorptiometry (DXA) method. The tests were carried out by a qualified and experienced technician in medical radiology using a densitometer (GE Healthcare Lunar Prodigy Advance DXA System, software version13.31). To ensure data quality the equipment has been calibrated daily using a known calibration standard and weekly using a step-wedge phantom, following manufacturer instructions.

Statistical analysis

Descriptive statistics were calculated for age, height, hip circumference, weight, BMI, % BF measured by DXA and estimated by BAI, and are expressed as mean ± standard deviation and minimum e maximum values. To evaluate the association between BAI and % BF assessed by DXA, we used Pearson's correlation coefficient. Paired sample t-test was used to test differences in mean % BF between BAI and DXA. Lin's concordance correlation coefficient [20] was used to assess the reproducibility between BAI and DXA. Mcbride [21] classifies the strength of agreement as poor (<0.90), moderate (0.90-0.95), substantial (0.95-0.99), and almost perfect (>0.99). The plot of the differences between DXA and BAI was showed by the Bland–Altman procedure [22]. Analyses were performed using a statistical software (MedCalc version 11.5.1, Mariakerke, Belgium) and we adopted a significance level of P < 0.05.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Age and body characteristics of the studied sample are in Table 1. The correlation analysis of % BF determined by DXA and BAI was significant (r = 0.65; P < 0.001). Paired t-test showed significant mean difference between methods [t(101) = −7.07; P < 0.0001].

Table 1. DXA measurements of % BF and anthropometric characteristics of participants in the study
VariableMean (SD)Min-Max
Age60.3 (9.8)35.0-83.0
Height (m)1.55 (5.4)1.44-1.66
Weight (kg)64.5 (8.4)45.1-95.0
BMI (kg/m2)26.9 (3.1)20.1-36.8
% BF (DXA, %)36.9 (6.2)22.5-48.8
% BF (BAI, %)33.6 (3.8)25.9-42.9
Hip (cm)99.3 (6.6)84.0-124.0

The strength of correlation between the % BF measured by DXA and that estimated by BAI in accordance with Lin's concordance correlation coefficient was C_b = 0.73. The plot of the differences between DXA and BAI showed by the Bland-Altman procedure [22] can be seen in Figure. 1

image

Figure 1. Agreement limits of Bland–Altman between the percentage of body fat measured by DXA and that estimated by BAI.

Download figure to PowerPoint

The mean (±SD) % BF of the DXA method was 36.91 (±6.21), compared with 33.61 (±3.77) for the BAI. The bias (SD) of the BAI is 3.29 ± 4.71% BF (95% CI = 2.37-4.22), indicating that the BAI measured lower % BF than the DXA. The lower limit of agreement −5.93 (95% CI = −7.52 to −4.34) and the upper limit of agreement of 12.53 (95% CI = 10.04-14.12), representing a confidence limit of the 18.4% BF [12.53 % BF − (−5.93 %BF)]. The percentage error is 50.01% (confidence limit of 18.46 divided by mean % BF value of 36.91 multiplied by 100).

The plot suggests that differences between the two methods exhibit a regular pattern obvious (proportional error), with overestimation of % BF by the BAI in subjects with lower % BF and underestimation in subjects with higher % BF (Figure 1).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

The used sample in this study presented values for weight and height measurements similar to those of the Brazilian population [23].

In this study, the correlation between % BF determined by DXA and that estimated by BAI was significant (r = 0.65), although lower than the observed one in the reference article [5] (r = 0.79). Paired t-test showed a significant mean difference between methods, with % BF measured by BAI showing values lower than determined by DXA. The result of Lin's concordance correlation coefficient was classified as poor [21]. The bias of the BAI 3.29 ± 4.71 % BF, represents a low accuracy while the limits of agreement show a low precision of the method. The percentage error of 50% determinated for the BAI is the highest value determined by the error-gram of the Critchley and Critchley [24], who is a enabling one to graphically determine the limits of agreement between two techniques. This value of 50% is determined by a limit of agreement of 30% and a limit of error of the test method of 40%, excessively high values of acceptable limits of agreement between two methods.

Bland-Altman plots showed a tendency to BAI to overestimated adiposity in subjects with lower BF% and underestimated it in obese subjects in relation to the used criterion measure (Figure 1), as observed in other populations [15, 17]. This fact is an aggravating error underestimation of BAI, it generates large percentage of false negatives (really obese individuals, but classified as eutrophic by BAI), failing to correctly identify cases of obesity.

This underestimation when applying BAI may be because of changes in body fat accumulation with age because it was higher in this study compared to the original population from which the equation was derived. To allow comparison's we have analyzed a subset of our sample with the same age range of Bergman's study. However, the results were similar to the whole sample analyzes. This can be explained by the average age still be much higher than the validation sample BAI and much of this group have passed through menopause. With aging occur changes in body composition, a decrease in muscle mass and changes in the pattern of body fat accumulation, with more deposit in the upper body [25]. In women, besides age, menopause is another factor that alters the pattern of body fat distribution. In postmenopausal American white women significant mean difference between measurements showed that BAI underestimated % BF measured by DXA [26]. Even without showing differences in total weight, postmenopausal women have a higher amount of total body fat, trunk fat, less fat in the lower limbs, and reduced muscle mass in the lower limbs than premenopausal women [27]. Thus, as the present study used individuals with a higher age than that which gave rise to the BAI equation, it is possible that older women may have reduced hip circumferences as a result of reduced muscle mass and fat in the lower limbs. Yet, they had a higher total body fat content, thus changing the relationship between circumference and body fat. However, we have no data about menopausal status to determine its influence in our results, this aspect has to be assumed as a study limitation.

As to the difference between the sexes, women have higher levels of % BF than men and differences in the distribution pattern of body fat [25], whereas for height, men have higher mean values than women [28]. From this information, one can assume that a method that aims to estimate % BF based on anthropometric measurements of hip circumference and height must propose gender-specific equations. These statements are confirmed by the results of studies that analyzed the BAI. Barreira et al. [29] observed differences between BAI estimations and % BF measured by DXA among sexes and races. In this study, both white and African American women showed lower % BF estimated by BAI than those determined by DXA, as observed in this study. For men of the same race, the BAI overestimated % BF. Johnson et al. [15] also observed similar results for European American men and women. The inclusion of both sexes can distort correlations between anthropometric measurements versus % BF, as observed by Vinknes et al. [17]. The proposition of a general equation for both sexes may incur estimate errors of % BF and its wide application may generate spurious results.

Ethnicity is another factor that greatly influences the shape and body composition of an individual. African American women have a higher amount of body fat when compared to Mexican American and European American women [27]. Hispanic individuals of both sexes with similar ages have been observed to have a lower height and weight than white and black individuals, with these women displaying a higher waist-hip index than the other two groups [30]. These differences in the anthropometrics profile and body composition among ethnic groups can change the relationship between anthropometric measurements and % BF, invalidating the equation in other populations. The extrapolation of an equation for estimating % BF based on measurements of body circumference and height for the Brazilian population should be viewed with caution because it is composed of a mixture of Amerindians, Europeans, and Africans, one of the most heterogeneous populations in the world and conferring their peculiar characteristics [31].

Based on these results, BAI was not an appropriate method for assessing % BF. The method showed poor concordance, low accuracy and precision, was statistically lower than that measured with DXA and underestimated the % BF especially in cases of obesity. For all the discussed factors, the proposal of an equation for % BF determination based on anthropometric measurements should be specific according to sex, age, and ethnicity, enabling their appropriateness and validity in populations with similar characteristics to that which gave rise to the equation.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References
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