Body composition predictions from bioelectric impedance.

The prediction of body composition variables from bioelectric impedance (BI) has considerable potential for use in surveys, because BI is reliable, and the equipment is portable (weight, 1.04 kg). The purpose of the present study was to determine if BI with selected anthropometric variables predicted %BF (percent body fat) accurately. Two groups of subjects were used from whom accurate anthropometric variables were ob' tained. The validation group of 148 healthy White adults (77 men; 71 women) aged 18 to 30 was used to formulate two parsimonious models for each sex to predict %BF from selected anthropometric variables, one without and one with stature2 divided by resistance (S2/R). The crossvalidation group, aged 18 to 30 years (19 White men; 29 White women), was used to assess the stability of equations derived from S2/R and anthropometric variables. Principal component analysis applied to 16 potential predictors showed five components explained most of the variation in %BF. All possible subsets regression procedure was employed to select the best equation on the basis of: (1) five predictors at most, (2) minimum root mean square error and (3) 0.1 level of significance. The multiple R2 and r.m.s.e. were not changed by the inclusion of S2/R in men. However, the inclusion of S2/R changed the R2 from 0.73 to 0.81 and the r.m.s.e. from 3.83% to 3.22% in women. Cross-validation of the equations that included S2/R showed the accuracy of prediction (coefficient of variation, 0.23 for men; 0.16 for women) was approximately the same as for the validation group. These findings indicated that the addition of S2/R to selected anthropometric variables significantly improved the prediction of %BF for women, but not for men. The quantification of human body composition is of considerable health importance because extremes of body fat have adverse health effects. The most accurate method of estimating body composition is the "direct" measurement of body * Presented in a Symposium entitled "The Bioelectrical Estimation of Body Composition" on April 11, 1986 at the Fifty-Fifth Annual Meeting of the American Association of Physical Anthropologists, Albuquerque, New Mexico. division of Human Biology, Department of Pediatrics, Wright State University, School of Medicine, Yellow Springs, Ohio 45387 2Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45435 3Division of Physical Education, Wright State University, Dayton, Ohio 45435 Human Biology, April 1987, Vol. 59, No. 2, pp. 221-233 © Wayne State University Press, 1987 This content downloaded from 40.77. 167.32 on Sun, 31 Jul 2016 04:24:48 UTC All use subject to http://about.jstor. org/terms 222 / SHUMEI GUO ET AL. density (BD) from underwater weighing. This method is based upon the assumption that the human body has two compartments: fat mass and fat-free mass (Siri 1961; Brozek 1963), although the calculation of body composition values from BD involves the use of "constraints", e.g., density of fat-free mass, that are not well-established (Roche 1987). Underwater weighing provides accurate measures of body density (BD), and it requires well-trained technicians and sophisticated equipment. Consequently, it is not practical for field studies. Thus, it is desirable to develop a simple method from which estimates of body composition can be obtained with accuracy. The estimation of body composition from bioelectric impedance (BI) is based on the principle that the conduction of a low frequency electric current in fat-free mass is greater than its conduction in fat. Because BI is simple to use, requires minimal participant compliance, is highly correlated with total body water (Kushner and Schoeller 1987) and the equipment is portable, it has great potential for use in surveys. Our primary interest was to determine if BI, with selected anthropometric variables, predicted %BF accurately. Materials and Methods Data were analyzed from two groups of subjects: a validation group and a cross-validation group. The validation group was composed of 148 healthy white adults (77 men; 71 women) aged 18 to 30 years. The cross-validation group consisted of 48 healthy white adults (19 men; 29 women) aged 18 to 30 years. The same measurement procedures were applied to the validation and crossvalidation groups. Weight in water, residual volume on land, selected anthropometric variables and bioelectrical resistance were measured as part of a larger study (Roche et al. in press, a; Siervogel et al. 1987). For each subject all measures were collected on the same day by two observers working independently. Underwater weights were measured at the Human Performance Laboratory, Division of Physical Education, Wright State University. The weighing apparatus consisted of a plastic chair suspended from a Chatillon scale into a tank containing approximately 1.8 m3 of water maintained at an average day-to-day temperature of 35°C. A tare weight for the chair and the water temperature were measured before each subject entered the tank. For each weighing, the participant sat in the chair, and then flexed at the waist until his/her body was completely submerged, simultaneously exhaling to maximum expiration. Underwater weight was recorded after bubbles stopped coming from the subject, and oscillations of the scale due to waves had subsided. Ten underwater weights were recorded for each subject, and the average of the three highest weights was used. Residual This content downloaded from 40.77. 167.32 on Sun, 31 Jul 2016 04:24:48 UTC All use subject to http://about.jstor. org/terms Bioelectrical Estimation of Body Composition / 223 lung volume was measured twice on land to the nearest 10 ml using the nitrogen washout method of Wilmore (1969) with a Gould M100B Pulmonary Function Analyzer. Body density (BD; gm/cm3) was calculated from the following equation: