Validation of near-infrared interactance and skinfold methods for estimating body composition of American Indian women.

PURPOSE: This study tested the predictive accuracy of the Jackson et al. skinfold (SKF) equations (sigma7SKF and sigma3SKF), a multi-site near-infrared interactance (NIR) prediction equation, and the Futrex-5000 NMR equation in estimating body composition of American Indian women (N = 151, aged 18-60 yr). METHODS: Criterion body density (Db) was obtained from hydrodensitometry at residual lung volume. RESULTS: Sigma7SKF significantly underestimated Db (P < 0.05). Sigma3SKF and Heyward's NIR equations significantly overestimated Db (P < 0.05). The Futrex-5000 NIR equation significantly underestimated percent of body fat (%BF) (P < 0.05). Prediction errors for SKF and multi-site NIR exceeded 0.0080 g x cc(-1). The SEE for Futrex-5000 was 5.5%BF. Thus, ethnic-specific SKF and NIR equations were developed. For the SKF model, the sigma3SKF (triceps, axilla, and suprailium) and age explained 67.3% of the variance in Db:Db = 1.06198316 -0.00038496(sigma3SKF) -0.00020362(age). Cross-validation analysis yielded r = 0.88, SEE = 0.0068 g x cc(-1), E = 0.0070 g x cc(-1), and no significant difference between predicted and criterion Db. For the NIR model, the hip circumference, sigma2AdeltaOD2 (biceps and chest), FIT index, age, and height explained 73.9% of the variance in Db:Db = 1.0707606 -0.0009865(hip circumference) -0.0369861(sigma2deltaOD2) + 0.0004167(height) + 0.0000866(FIT index) -0.0001894(age). Cross-validation yielded r = 0.85, SEE = 0.0076 g x cc(-1), E = 0.0079 g x cc(-1), and a small, but significant, difference between predicted and criterion Db. CONCLUSIONS: We recommend using the ethnic-specific SKF and NIR equations developed in this study to estimate Db of American Indian women.

The fatness-specific bioelectrical impedance analysis equations of Segal et al: are they generalizable and practical?

The fatness-specific bioelectrical impedance analysis (BIA) equations of Segal et al (Am J Clin Ntr 1988;47: 7-14; Segal equations) have been shown to be generalizable across sex, ethnicity, age, and degrees of adiposity. However, these fatness-specific equations require an a priori determination of percentage body fat (%BF) by using a skinfold equation or densitometry to categorize subjects into obese or nonobese groups. These procedures negate the use of BIA as a fast and simple method. It was hypothesized that the average of the Segal nonobese and obese fatness-specific equations (BIA average method) could be used in lieu of the skinfold method for categorizing subjects who are not obviously lean or obese. In phase 1 these three methods were compared for a subsample of 59 women who were not obviously lean or obese. The %BF of 75% of these subjects was accurately estimated within 3.5%BF by using the BIA average method whereas only 71% and 46% were accurately estimated by fusing the densitometric and skinfold methods, respectively. In phase 2, the predictive accuracy of the Segal fatness-specific equations, used in combination with the BIA average method, was compared with other BIA equations published previously for 602 American Indian, Hispanic, and white women and men. The Segal fatness-specific equations yielded the smallest prediction error (SEE = 2.22 kg for women and 3.59 kg for men) and the %BF of 70% of the subjects was accurately estimated within 3.5%BF compared with 24-59% for other BIA equations. Therefore, we recommend using the Segal fatness-specific and average equations to assess body composition in heterogeneous populations.

Predictive accuracy of bioelectrical impedance in estimating body composition of Native American women.

The predictive accuracy of race-specific and fatness-specific bioelectrical impedance analysis (BIA) equations for estimating criterion fat-free mass (FFM) derived from two-component (2C) and multicomponent (MC) models was examined. Body density (Db) of Native American women (n = 151) aged 18-60 y was measured by hydrostatic weighing at residual volume. Total body bone ash was obtained by dual-energy, x-ray absorptiometry. Cross-validation of the Rising (5), Segal (3), and Gray (4) equations against FFM2C yielded high correlation coefficients (0.86-0.95) and acceptable SEEs (1.47-2.72 kg). Cross-validation of these equations against criterion FFMMC, with Db adjusted for total body mineral, yielded similar correlation coefficients (0.82-0.94) and SEEs (1.69-2.80 kg). However, each BIA equation significantly overestimated FFMMC. A new race-specific BIA equation based on an MC model was developed: FFMMC = 0.001254(HT2)-0.04904(R) + 0.1555(WT) + 0.1417(Xc) - 0.0833(AGE) + 20.05 (R = 0.864, and SEE = 2.63 kg).

Body composition of Native-American women estimated by dual-energy X-ray absorptiometry and hydrodensitometry.

In the present sample, the Native-American women varied in age (18-60 y) and fatness (23.0-57.4% BF). The cross-validation analysis for %BF estimated by DXA for this sample yielded a high validity coefficient (r = 0.89), and the average %BFDXA (37.3%) and %BFHW (37.6%) did not differ significantly. The prediction error (3.28% BF) was less than the theoretical expected value, given the wide range in age and fatness in this sample. Thus, it appears that DXA may be a viable alternative method for estimating the %BF of a diverse group of Native-American women. The DXA method is more practical than hydrostatic weighing, especially for subjects who are uncomfortable in the water. Also, DXA estimates of bone mineral may lead to improved estimates of FFB density for different ethnic populations.

Relationship of optical density and skinfold measurements: effects of age and level of body fatness.

We examined relationships between skinfold (SKF) and optical density (delta OD) measurements across age and levels of body fatness (%BF) for 151 women, 20 to 72 years. There were significant (p < .05) relationships between delta ODs and SKFs at all sites, except the thigh. The interaction (SKF x Age) was significant (p < .05) for pectoral and biceps delta ODs. Slope comparisons indicated the relationships for younger (29 years) and older (59 years) women differed significantly from zero and each other (p < .05). Analysis of SKF x %BF interactions revealed that relationships between SKFs and delta ODs at the pectoral and biceps sites for leaner (22% BF) women differed significantly from zero (p < .05) and were larger than those for obese (39% BF) women (p < or = .05). Thus, the relationship between SKFs and delta ODs is stronger for younger and leaner women compared to older and fatter women. These findings may reflect differences in fat layering due to age or body fatness and provide insight as to why the manufacturer's near-infrared (NIR) equation significantly underestimates the %BF of obese women.

Predictive accuracy of three field methods for estimating relative body fatness of nonobese and obese women.

Three methods of body composition assessment were used to estimate percent body fat (%BF) in nonobese (n = 77) and obese (n = 71) women, 20-72 yrs of age. Skinfolds (SKF), bioelectrical impedance (BIA), and near-infrared interactance (NIR) methods were compared to criterion-derived %BF from hydrostatic weighing (%BFHW). Nonobese subjects had < 30% BFHW and obese subjects had > or = 30% BFHW. The Jackson, Pollock, and Ward SKF equation and the manufacturer's equations for BIA (Valhalla) and NIR (Futrex-5000) were used. For nonobese women there were no significant differences between mean %BFHW and %BFSKF, %BFBIA, and %BFNIR. The rs and SEEs were 0.65 and 3.4% BF for SKF, 0.61 and 3.6% BF for BIA, and 0.58 and 3.7% BF for NIR for nonobese subjects. For obese women, mean %BFHW was significantly underestimated by the SKF, BIA, and NIR methods. The rs and SEEs for the obese group were 0.59 and 3.4% BF for SKF, 0.56 and 3.5% BF for BIA, and 0.36 and 3.9% BF for NIR. The total errors of the equations ranged from 5.6 to 8.0% BF in the obese group. It is concluded that all three field methods accurately estimate %BF for nonobese women; however, none of the methods is suitable for estimating %BF for obese women.

Coronary heart disease knowledge test: developing a valid and reliable tool.

This study tested the validity and reliability of a written test designed to assess knowledge of coronary heart disease (CHD) and its risk factors. The subjects were 93 males diagnosed with CHD. Subjects were classified into a treatment group (n = 48) or a control group (n = 45) based on whether or not they participated in a cardiac rehabilitation program (CRP). An additional 38 subjects were used to pilot test the original form of the knowledge test, which consisted of 80 multiple-choice questions. Content validity was established by a five-member jury of cardiac rehabilitation experts. Each question was rated using a Likert-type scale. Questions that did not receive an average rating of at least four were eliminated. The revised form was pilot tested for validity and internal consistency with the discrimination index (point biserial correlation coefficient) and the Kuder-Richardson formula 20 (KR-20). Questions with a discrimination index of less than 0.14 were eliminated; thus, the final form of the test consisted of 40 questions. Validation of this test yielded difficulty ratings (DRs) between 0 percent and 98 percent, with an average DR of 63 percent. Construct validation indicated that the average test score of subjects participating in a CRP was significantly higher than that of non-participants (t = 3.51, df = 91, p less than or equal to 0.01). The internal-consistency reliability of the test was 0.84. The results indicate that this test is a valid and reliable tool for assessing patients' knowledge of CHD and its risk factors.