M. D. Van Loan

Validation of fan beam dual energy x ray absorptiometry for body composition assessment in adults aged 18–45 years

Background: Pencil beam dual energy x ray absorptiometry (DXA) has been shown to provide valid estimates of body fat (%BF), but DXA fan beam technology has not been adequately tested to determine its validity. Objective: To compare %BF estimated from fan beam DXA with %BF determined using two and three compartment (2C, 3C) models. Methods: Men (n  =  25) and women (n  =  31), aged 18–41 years, participated in the study. Body density, from hydrostatic weighing, was used in the 2C estimate of %BF; DXA was used to determine bone mineral content (BMC) for the 3C estimate of %BF calculated using body density and BMC (3CBMC). DXA was also used to determine %BF. Analysis of variance was used to test for significant differences in %BF between sexes and among methods. Results: Women were significantly shorter, weighed less, had less fat free mass, and a higher %BF than men. No significant differences were found among methods (2C, 3CBMC, DXA) for determination of %BF in either sex. Although not significant, Bland-Altman plots showed that DXA gave higher values for %BF than the 2C and 3CBMC methods. Conclusion: DXA determination of %BF was not different from that of the 2C and 3CBMC models in this group of young adults. However, to validate fan beam DXA fully as a method for body composition assessment in a wide range of individuals and populations, comparisons are needed that use a 4C model with a measure of total body water and BMC.

Bone Mineral and Predictors of Bone Mass in White, Hispanic, and Asian Early Pubertal Girls

Differences in bone among racial/ethnic groups may be explained by differences in body size and shape. Previous studies have not completely explained differences among white, Asian, and Hispanic groups during growth. To determine racial/ethnic differences and predictors of bone mass in early pubertal girls, we measured bone mineral content (BMC) in white, Hispanic, and Asian sixth-grade girls across six states in the United States. We developed models for predicting BMC for the total-body, distal radius, total-hip, and lumbar spine for 748 subjects. For each of the bone sites, the corresponding area from dual-energy X-ray absorptiometry (DXA) was a strong predictor of BMC, with correlations ranging 0.78–0.98, confirming that larger subjects have more BMC. Anthropometric measures of bone area were nearly as effective as bone area from DXA at predicting BMC. For total-body, distal radius, lumbar spine, and total-hip BMC, racial/ethnic differences were explained by differences in bone area, sexual maturity, physical activity, and dairy calcium intake. Bone size explained most of the racial/ethnic differences in BMC, although behavioral indicators were also significant predictors of BMC.

Body composition in disease: what can we measure and how can we measure it?

Abstract.This manuscript presents a brief overview of the topic of body composition in disease. The purpose of this paper is threefold: (1) to present examples of diseases in which body composition assessment might provide valuable information to physicians and other clinical personnel in patient care; (2) provide basic information on the types of methodologies available for various aspects of body composition assessment; and (3) give a brief review of some of the research literature available on the topic of body composition use in disease. Materials in this paper should not be interpreted as providing all the relevant information in this area of research, but the paper does represent a limited overview of the topic.