Cross-Validation of Resting Metabolic Rate Prediction Equations.

BACKGROUND: Resting metabolic rate (RMR) measurement is time consuming and requires specialized equipment. Prediction equations provide an easy method to estimate RMR; however, their accuracy likely varies across individuals. Understanding the factors that influence the accuracy of RMR predictions will help to revise existing, or develop new and improved, equations. OBJECTIVE: Our aim was to test the validity of RMR predicted in healthy adults by the Harris-Benedict, World Health Organization, Mifflin-St Jeor, Nelson, Wang equations, and three meta-equations of Sabounchi. DESIGN: Predicted RMR was tested for agreement with indirect calorimetry. PARTICIPANTS/SETTING: Men and women (n=30) age 18 to 65 years from Grand Forks, ND, were recruited and included for analysis during spring/summer 2014. Participants were nonobese or obese (body mass index range=19 to 39) and primarly white. MAIN OUTCOME MEASURE: Agreement between measured (indirect calorimetry) and predicted RMR was measured. STATISTICAL ANALYSIS: The methods of Bland and Altman were employed to determine mean bias (predicted minus measured RMR, kcal/day) and limits of agreement between predicted and measured RMR. Repeated-measures analysis of variance was used to test for bias in RMR predicted from each equation vs the measured RMR. RESULTS: Bias (mean±2 standard deviations) was lowest for the Harris-Benedict (-14±378 kcal/24 h) and World Health Organization (-25±394 kcal/24 h) equations. These equations also predicted RMR that were not different from measured. Mean RMR predictions from all other equations significantly differed from indirect calorimetry. The 2 standard deviation limits of agreement were moderate or large for all equations tested, ranging from 314 to 445 kcal/24 h. Prediction bias was inversely associated with the magnitude of RMR and with fat-free mass. CONCLUSIONS: At the group level, the traditional Harris-Benedict and World Health Organization equations were the most accurate. However, these equations did not perform well at the individual level. As fat-free mass increased, the prediction equations further underestimated RMR.

Felder-Soloman's Index of Learning Styles: internal consistency, temporal stability, and factor structure.

BACKGROUND: Strategies to facilitate learning include using knowledge of students' learning style preferences to inform students and their teachers. PURPOSE: Aims of this study were to evaluate the factor structure, internal consistency, and temporal stability of medical student responses to the Index of Learning Styles (ILS) and determine its appropriateness as an instrument for medical education. METHODS: The ILS assesses preferences on four dimensions: sensing/intuitive information perceiving, visual/verbal information receiving, active/reflective information processing, and sequential/global information understanding. Students entering the 2002-2007 classes completed the ILS; some completed the ILS again after 2 and 4 years. RESULTS: Analyses of responses supported the ILS's intended structure and moderate reliability. Students had moderate preferences for sensing and visual learning. CONCLUSIONS: This study provides evidence supporting the appropriateness of the ILS for assessing learning style preferences in medical students.

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.

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.

Interaction of clothing and body mass index affects validity of air-displacement plethysmography in adults.

OBJECTIVE: We determined the effect of clothing type on the validity of air-displacement plethysmography (ADP) to estimate percentage of body fat (%BF) and ascertain if these effects differ by body mass index (BMI). METHODS: The %BF by dual x-ray absorptiometry (DXA) and %BF, density, and body volume by ADP were assessed in 132 healthy adults classified by normal (N; 18.5-24.9 kg/m2), overweight (OW; 25-29.9 kg/m2), and obese (OB; 30-39.9 kg/m2) BMIs. RESULTS: Compared with DXA, ADP underestimated (P < 0.0001) %BF from scrubs (SC) and t-shirt/shorts (TS) in N (11.4%; 8.6%) and OW (6.8%; 4.9%) BMI groups, respectively. ADP compared with DXA overestimated (P < 0.0006) %BF in the OW group (1.2%), but underestimated (P < 0.0001) it in the N group (2.4%). ADP also overestimated (P < 0.006) %BF in the OB group wearing spandex (SP; 4.8%), but not in those wearing SC (0.7%; P = 0.10) and TS (0.5%; P = 0.22) versus DXA. CONCLUSION: All three clothing types showed significant error in estimating %BF with ADP compared with DXA in N and OW BMI. Use of spandex provided the least error and is the preferred attire to obtain valid body composition results when testing N and OW subjects. However, SP provided the greatest error in the OB group. Error in ADP %BF in OB was minimal in SC and TS and similar to the within-subject variability in %BF estimates with ADP. Thus, TS and SC are acceptable alternatives to SP in adults with excess body weight.

Assessment of change in hydration in women during pregnancy and postpartum with bioelectrical impedance vectors.

OBJECTIVE: This study tested the hypothesis that bioelectrical impedance vectors, group and individual, are valid indicators of total body water (TBW) and hydration status in women experiencing fluid gain and loss during and after pregnancy. METHODS: We measured TBW, assessed with D(2)O dilution, and resistance (R) and reactance (Xc), determined with 800 microA at 50 kHz and standardized for height (H) and plotted on a bivariate (R-Xc) graph, in 15 women, 21-37 y of age, longitudinally before and during pregnancy and postpartum (PP). RESULTS: Body weight (61.9 +/- 2.3 to 75.5 +/- 2.3 kg) and TBW (31.4 +/- 1.1 to 38.2 +/- 1.1 L) increased (P < 0.05) from before pregnancy to the third trimester of pregnancy and decreased PP (67.0 +/- 2.3 kg and 32.7 +/- 1.1 L, P < 0.05). R/H and Xc/H decreased during pregnancy (P < 0.05, 361 +/- 10 to 318 +/- 10 and 44 +/- 1 to 36 +/- 1 omega/m, respectively) and increased PP (P < 0.05, 355 +/- 10 and 41 +/- 1 Omega/m). Vector length decreased (P < 0.05, 363 +/- 10 to 320 +/- 10 Omega) during pregnancy and increased PP (P < 0.05, 357 +/- 10 Omega). Changes in vector length and TBW during pregnancy and PP were correlated (r = -0.599, P < 0.001). Women with vectors exceeding a 75% tolerance interval had greater TBW gain (10-12 versus 5-6 L) during pregnancy compared with other women with vectors within this tolerance level. CONCLUSION: These findings indicate that impedance vectors provide quantitative evidence of hydration status during pregnancy and that the impedance vector method is useful in monitoring hydration status in pregnancy.

Chromium picolinate supplementation in women: effects on body weight, composition, and iron status.

OBJECTIVE: This study tested the hypothesis that supplementation of chromium picolinate (CrPic), 200 microg Cr/d, compared with an equivalent amount of picolinic acid (1720 microg) in CrPic and placebo, decreases body weight, alters body composition, and reduces iron status of women fed diets of constant energy and nutrients. METHODS: We fed 83 women nutritionally balanced diets, used anthropometry and dual x-ray absorptiometry to assess body composition, and measured serum and urinary Cr and biochemical indicators of iron status before and serially every 4 wk for 12 wk in a double-blind, randomized trial. RESULTS: CrPic supplementation increased (P < 0.0001) serum Cr concentration and urinary Cr excretion compared with picolinic acid and placebo. CrPic did not affect body weight or fat, although all groups lost (P < 0.05) weight and fat; it did not affect fat-free, mineral-free mass or measurements of iron status. CONCLUSION: Under conditions of controlled energy intake, CrPic supplementation of women did not independently influence body weight or composition or iron status. Thus, claims that supplementation of 200 microg of Cr as CrPic promotes weight loss and body composition changes are not supported.

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.

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.