The aim of this study was to investigate the accuracy of BIA in the measurement of total body composition and regional fat and the fat free mass in the healthy young adults. Four hundred and three healthy young adults (167 women and 236 men) aged 18-29 years were recruited from the Mid-West region of Ireland. Multi frequency, eight-polar bioelectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DXA) were used to measure the total body and segmental (arm, leg and trunk) fat mass and the fat free mass. BIA was found to underestimate the percentage total body fat in men and women (p < 0.001). This underestimate increased in men with >24.6% body fat and women with >32% body fat (p < 0.001). Fat tissue mass in the trunk segment was overestimated by 2.1 kg (p < 0.001) in men and underestimated by 0.4 kg (p < 0.001) in women. BIA was also found to underestimate the fat free mass in the appendages by 1.0 kg (p < 0.001) in men and 0.9 kg (p < 0.001) in women. Compared to dual energy X-ray absorptiometry, bioelectrical impedance analysis underestimates the total body fat mass and overestimates fat free mass in healthy young adults. BIA should, therefore, be used with caution in the measurement of total body composition in women and men with >25% total body fat. Though statistically significant, the small difference (~ 4%) between the methods indicates that the BIA may be used interchangeably with DXA in the measurement of appendicular fat free mass in healthy young adults.
The search for valid, reliable and inexpensive methods of measuring body composition is an ongoing issue for many researchers. In particular, the measurement of subcutaneous adipose tissue (SAT) is carried out by numerous methods, each with its own drawbacks. Skinfold thickness measurement is the most common in-field method, but it is limited by its tendency to deform the adipose layer, by the limited caliper opening which prevents measurement of larger skinfolds, and the lack of correction for elastic properties of tissue between individuals. Therefore non-invasive field measures which overcome these limitations would be desirable. Ultrasound scanning provides such a device due to its portability and availability, allowing reduced tissue compression and on-screen views of the adipose tissue. Despite a number of papers referring to the use of ultrasound for measuring adipose tissue, the method of measurement has not been fully described. This paper describes our work in determining an accurate method for the measurement of SAT at different body sites, including a comparison of scanning directions and sites. We also describe our investigations into the degree to which compression force through the transducer affects adipose tissue measurement, and the reliability and sensitivity of our methods. We conclude with a recommended reliable scanning protocol for the measurement of SAT.
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