William A. Siders

Validity of segmental multiple-frequency bioelectrical impedance analysis to estimate body composition of adults across a range of body mass indexes.

OBJECTIVE We compared body composition estimates using an eight-electrode, segmental, multiple-frequency bioelectrical impedance analysis (segmental MF-BIA) and dual x-ray absorptiometry (DXA) in a group of healthy adults with a range of body mass indexes (BMIs). METHODS Percentage of body fat (%BF), fat-free mass, and fat mass assessed by DXA and segmental MF-BIA in 132 healthy adults were classified by normal (N; 18.5-24.9 kg/m(2)), overweight (OW; 25-29.9 kg/m(2)), and obese (OB; 30-39.9 kg/m(2)) BMI. RESULTS Compared with DXA, segmental MF-BIA overestimated %BF in the OB BMI group (3.4%; P < 0.0001). MF-BIA overestimated %BF among men (0.75%; P < 0.006) and women (0.87%; P < 0.006) and underestimated it in the N BMI group (-1.56%; P < 0.0001); %BF was not different between methods in the OW BMI group. Error in %BF determined by segmental MF-BIA and DXA increased as %BF increased (r = 0.42, P < 0.0001). Waist circumference was the only significant predictor of systematic error in %BF between MF-BIA and DXA (r = 0.60, P < 0.0001). CONCLUSION Eight-electrode, segmental MF-BIA is a valid method to estimate %BF in adults with BMI classified as N and OW, but not as OB. Estimation of trunk resistance with current segmental MF-BIA devices may explain the underestimation of %BF in the adults with OB BMI. Further examination of the effect of waist circumference and body fat distribution on the accuracy of BIA measurements is warranted.

Validity and accuracy of regional bioelectrical impedance devices to determine whole-body fatness

OBJECTIVE Growing emphasis on obesity as a risk factor for chronic diseases and commercial availability of impedance devices for the at-home assessment of body fatness have stimulated the need for a critical evaluation of the validity of these instruments. This study determined the reproducibility and accuracy of two commercial impedance devices that use upper (hand-to-hand) or lower (foot-to-foot) body contact electrode placements in adults with a wide range of body fatness. METHODS Body composition was assessed with dual x-ray absorptiometry in apparently healthy adults (62 women and 48 men) ages 21 to 60 y, with a range in body mass index of 18.6 to 40.5 kg/m2. Variability in body fatness predicted with the regional body impedance devices was determined in 10 adults on 5 consecutive d. A 50-kHz, tetrapolar bioelectrical impedance plethysmograph with surface electrode placements on the upper and lower limbs was used to determine reference regional and whole-body impedance values. RESULTS Variability in body mass (1%) over 5 d was less than body fatness predicted with the upper (2-10%) and lower (3-5%) body devices. Regional and whole-body impedance values were different (P < 0.05) in the women, whereas upper and lower body values were lower (P < 0.05) than whole-body impedance in the men. Dual x-ray absorptiometric determinations of body fatness were similar to predictions based on models derived from physical characteristics (age, stature, body mass, and sex) but significantly different (P < 0.05) from estimates from the impedance devices, which underestimated body fatness. Bias in predictions of body fatness with the regional devices was systematically (P < 0.0001) related to body fatness. CONCLUSION Use of regional impedance devices to assess body fatness is limited by a lack of precision and accuracy.

Soft tissue composition of pigs measured with dual x-ray absorptiometry: comparison with chemical analyses and effects of carcass thicknesses.

Evidence of the validity and accuracy of dual x-ray absorptiometry (DXA) to measure in vivo body composition is limited. We compared DXA estimates made in prone and side positions with measurements of chemical composition of 20 pigs (10 barrows and 10 gilts) weighing 52-113 kg. DXA yielded similar estimates of body composition in prone and side positions. DXA estimates of body composition were significantly correlated with reference compositional values (r2 = 0.927-0.998). No significant differences were found for determinations of body weight, fat mass (FM), fat free mass (FFM), bone-free, and fat-free mass (BFFFM) between DXA and chemical determinations. DXA significantly underpredicted percent fat (% fat); it underestimated FM (20%, P > 0.05), and overestimated FFM and BFFFM (6 and 9%, respectively, P > 0.05). Differences between individual determinations of FM and % fat by chemical analyses and DXA were significantly correlated with mean values. No significant correlations were found between the differences for weight, FM, % fat, FFM and BFFFM and measurements of carcass breadth (19-28 cm) and width (15-25 cm). Total errors in determination of DXA body composition variables were similar with body thicknesses less than and greater than 24 cm. These findings indicate that DXA is a valid and accurate method for determination of soft tissue composition. Initial problems with DXA determinations of % fat apparently have been reconciled partially with revisions in soft tissue analytic software.

Altered metabolic response of iron-deficient women during graded, maximal exercise.

SummaryMetabolic responses during a standardized, progressive, maximal work capacity test on a cycle ergometer were studied in 11 women, mean age 28 (SEM 2) years, at admission to the study, after their body iron stores were depleted by diet, phlebotomy and menstruation for about 80 days and after iron repletion by diet for about 100 days, including daily iron supplementation (0.9 mmol iron as ferrous sulfate) for the last 14 days of repletion. Iron depletion was characterized by a decline (P<0.05) in hemoglobin, ferritin and body iron balance. Iron repletion, including supplementation, increased (P<0.05) hemoglobin, ferritin and iron balance. No changes were observed in cardiovascular and ventilatory responses or peak oxygen uptake. Iron depletion was associated with a reduced (P<0.05) rate of oxygen utilization, total oxygen uptake and aerobic energy expenditure, and elevated (P<0.05) peak respiratory exchange ratio and post-exercise concentration of lactate. Reduction of body iron stores without overt anemia affects exercise metabolism by reducing total aerobic energy production and increasing glycolytic metabolism.

Validation of dual x-ray absorptiometry for body-composition assessment of rats exposed to dietary stressors.

Evidence of the validity and accuracy of dual x-ray absorptiometry (DXA) to measure soft-tissue composition of laboratory rats with altered body composition associated with nutritional perturbations is lacking. We compared DXA determinations made in prone and supine positions with measurements of chemical composition of 49 male, weanling Sprague-Dawley rats that were fed the basal AIN-93 growth diet, were fed the basal diet modified to contain 30% fat, were fasted for 2 d, were limit fed 6 g of the basal diet daily for 1 wk, or were treated with furosemide (10 mg/kg intraperitoneally 2 h before DXA). DXA produced similar estimates of body mass and soft-tissue composition in the prone and supine positions. DXA estimates of body composition were significantly correlated with reference composition values (R(2) = 0.371-0.999). DXA discriminated treatment effects on body mass, fat-free and bone-free mass, fat mass, and body fatness; it significantly underestimated body mass (1% to 2%) and fat-free and bone-free mass (3%) and significantly overestimated fat mass and body fatness (3% to 25%). The greatest errors occurred in treatment groups in which body mass was diminished and body hydration was decreased. These findings suggest that DXA can determine small changes in fat-free, bone-free mass in response to obesity and weight loss. Errors in DXA determination of fat mass and body fatness associated with extra corporeal fluid and dehydration indicate the need for revision of calculation algorithms for soft-tissue determination.

Association of dominant somatotype of men with body structure, function during exercise, and nutritional assessment†

This study examined the hypothesis that somatotype determines body structure, functional responses at peak exercise, and nutritional status of 63 men ages 18–40 years who lived under controlled conditions. Data were grouped by dominant somatotype to emphasize differences in body types. Dominant ectomorphs (n = 19) had less (P < 0.05) body weight, fat weight, and percent body fat than endomorphs (n = 14) and mesomorphs (n = 30). Fat‐free weight (FFW), total body potassium (TBK), and body cell mass (BCM), normalized for stature, were lower (P < 0.05) in the ectomorphs than in the endomorphs and mesomorphs. Comparisons between measured and predicted FFW and TBK showed that only the ectomorphs had less (P < 0.05) FFW and TBK than expected. Although all groups had the same peak power output, the ectomorphs had different functional responses during peak exercise. Ectomorphs had the greatest respiratory exchange ratio (P < 0.05), ventilatory equivalent for oxygen, and end‐exercise plasma lactate concentrations (P < 0.05), and lowest peak oxygen uptake (L/min; P < 0.05). Nutrient intakes and blood biochemical markers of nutritional status were within the range of normal values in all groups. Correlations between measures of body structure, function, and nutritional status and dominant somatotype components were calculated after controlling for the effects of the other two somatotype components. Partial correlations were variable, with significant correlations ranging from −0.30 to 0.87. These data indicate that ectomorphs, as compared to endomorphs and mesomorphs, have deficits in FFW and BCM which are associated with differences in functional capacity. Am. J. Hum. Biol. 12:167–180, 2000. Published 2000 Wiley‐Liss, Inc.

Relationship between body composition and the components of somatotype

In a sample of 422 adults (200 females and 222 males) aged 18–73 years, the relationship was determined between somatotype estimated by the Health‐Carter (Am. J. Phys. Anthropol. 27:57–74, 1967) method and body composition variables determined by using hydrodensitometry (HD) and Bioelectrical Impedance Analysis (BIA).

Body density estimates from upper-body skinfold thicknesses compared to air-displacement plethysmography.

BACKGROUND & AIMS Determine the accuracy of body density (Db) estimated with upper-body skinfold thickness (SFT) measurements compared to air-displacement plethysmography (ADP) and ascertain whether body mass index (BMI) impacts the accuracy of SFT to assess Db. METHODS We estimated Db with SFT and ADP in 131 healthy men and women with normal (N; 18.5-24.9kg/m(2)), overweight (OW; 25-29.9kg/m(2)), and obese (OB; 30-39.9kg/m(2)) BMI. RESULTS Compared with ADP, SFT overestimated (p<0.05) Db in OW and OB females and in OB males (-0.0047, -0.0164 and -0.0119g/cc, respectively), and underestimated (p<0.05) Db in N females and males (0.0050 and 0.0068g/cc, respectively) but did not differently estimate Db in OW males. The gender by BMI group interaction was not significant. SFT underestimated (p<0.05; 0.0058g/cc) Db in the N and overestimated (p<0.05; 0.0113g/cc) Db in the OB BMI groups. The error in predicting Db did not change significantly over the range of Db within the N (r=0.239, p=0.06) and OB (r=0.160, p=0.934) BMI groups. Limits of agreement were -0.0165 to 0.0284g/cc and -0.0365 to 0.0085g/cc for the N and OB BMI groups, respectively. The error of estimating Db with SFT was correlated with mean Db in the aggregate sample (r=0.495, p<0.0001) and the OW group (r=0.394, p<0.009). The regression-based limits of agreement were +/-0.0226g/cc in the total group and +/-0.0168g/cc in the OW group. CONCLUSIONS Although SFT offer practical advantages, the validity of SFT to estimate Db among individuals with N and OB BMI is adversely affected.