Scott B Going

PMID: 6530218;Abstract:

The estimation of body fatness by the densitometric method assumes a constant density of the fat-free body. Water constitutes the largest single component of the fat-free body and because of its relatively low density (.9934 gm/cc at 37°C) exerts the greatest influence on the density of the fat-free body. The purpose of this study was to test the assumption that the water content of the fat-free body (% water-FFB) is constant during growth and development. The sample consisted of 292 Black and White males and females (ages 8-30 years) and was classified via maturational assessment as prepubertal, (N = 54), pubertal (N = 50), postpubertal (N = 107) and adult (N = 81). Body water was measured by deuterium oxide dilution and body density was measured by the underwater weighing method. Body water as a percentage of body weight (% water-BW) was higher (p .01) for males (X̄ = 61.6%) than females (X̄ = 55.8%) with the greatest difference observed in the pubertal, postpubertal and adult levels. This finding likely reflected the increased relative fatness of females at puberty and is in agreement with skinfold thickness measurements. The % water-FFB progressively decreased from prepubescence to adulthood by 2.8% overall at a rate of 0.38% per year for both sexes with the lowest values found in the adult samples. Although the % water-FFB of the prepubertal and pubertal groups was similar (p > .05), both groups were significantly (p .01) higher than the postpubertal and adult groups, and the postpubertal groups was higher (p .05) than the adult group. Moreover, the % water-FFB was lower (p .05) for males (X̄ = 73.5%) than females (X̄ = 74.2%). No difference in % water-FFB was found between the Black and White samples. These findings suggest that the water content of the FFB is not constant during growth and development and that adult equations for estimating fat from density and other indirect methods may not be appropriate for children, overestimating fatness by at least 4%.

Abstract:

Estimation of energy requirements relies on adequate values of basal metabolic rate (BMR). Prediction equations recommended for international use have been shown to overestimate BMR in populations living in the tropics. We have previously shown the inadequacy of these equations in samples of Brazilians living in tropical and temperate regions of the country. We sought to investigate whether BMR could adequately be estimated by prediction equations in a sample of Brazilians living in a different setting: the Sonoran desert of the Southwestern USA. BMR was measured under standard conditions in 33 subjects (14 men). Mean bias (estimated-measured) varied from 404.4 to 708.6 kJday^-1 in women and 566.8 to 1122.8 kJday^-1 in men, representing 8.5-15 and 8.9-17.6% overestimation, respectively, using the Schofield equations. Bland and Altman analyses showed large, relevant limits of agreement. The results using the recommended equations for the American population (IOM, 2005) were only 2% different from the Schofield equations. The Harris and Benedict equations yielded higher overestimations (15.0 and 16.8% for women and men, respectively) and the Henry and Rees equations also overestimated BMR (8.5 and 8.9%) even though they were developed for populations from the tropics, although to a lesser degree. It is concluded that the equations currently recommended for international use are not appropriate for Brazilians living in the Southwestern USA.

PMID: 10584055;Abstract:

Background: Valid and practical methods based on health-related criteria for obesity screening in children and adolescents are not available. Arbitrarily defined body mass index (BMI) cutoffs have been proposed to select adolescents at high risk of developing obesity in adulthood. Objective: We assessed the usefulness of BMI, triceps skinfold thickness, and upper arm girth for screening for obesity by using a health-related definition of obesity (≥25% body fat in boys and ≥30% body fat in girls) and a criterion method (dual-energy X-ray absorptiometry) that estimates percentage fat without the potential bias associated with other methods in adolescents. Design: This was a cross-sectional study of Portuguese boys (n = 165) and girls (n = 163) aged 10-15 y. Nonparametric receiver operating characteristic (ROC) analysis was used to define the best tradeoff between true-positive and false-positive rates. Results: True-positive rates ranged from 67% to 87% and from 50% to 100% in girls and boys, respectively, and false-positive rates ranged from 0% to 19% and from 5% to 26%, respectively. For children aged 1 0-11 y, the areas under the curves (AUCs) for ROCs, an index of diagnostic accuracy, were close to 1.0, suggesting very good accuracy. For older boys and girls, AUCs for triceps skinfold thickness were similar to or greater than AUCs for BMI and upper arm girth. Conclusions: The results suggest that triceps skinfold thickness gives the best results for obesity screening in adolescents aged 10-15 y. BMI and upper arm girth were reasonable alternatives, except in 14-15-y-old boys, in whom both indexes were only marginally able to discriminate obesity.