Development of a single-frequency bioimpedance prediction equation for fat-free mass in an adult Indigenous Australian population.

BACKGROUND/OBJECTIVES: To describe the development of a single-frequency bioimpedance prediction equation for fat-free mass (FFM) suitable for adult Aboriginal and Torres Strait Islander peoples with and without diabetes or indicators of chronic kidney disease (CKD). SUBJECTS/METHODS: FFM was measured by whole-body dual-energy X-ray absorptiometry in 147 adult Indigenous Australians. Height, weight, body circumference and resistance were also measured. Adults with and without diabetes and indicators of CKD were examined. A random split sample with internal cross-validation approach was used to predict and subsequently validate FFM using resistance, height, weight, age and gender against measured FFM. RESULTS: Among 147 adults with a median body mass index of 31 kg/m(2), the final model of FFM was FFM (kg)=0.432 (height, cm(2)/resistance, ohm)-0.086 (age, years)+0.269 (weight, kg)-6.422 (if female)+16.429. Adjusted R(2) was 0.94 and the root mean square error was 3.33 kg. The concordance was high (rc=0.97) between measured and predicted FFM across a wide range of FFM (31-85 kg). CONCLUSIONS: In the context of the high burden of diabetes and CKD among adult Indigenous Australians, this new equation for FFM was both accurate and precise and based on easily acquired variables (height, weight, age, gender and resistance) among a heterogeneous adult cohort.

Tissue composition changes and secondary lymphedema.

BACKGROUND: The aim of this study was to determine the impact of dominance and severity on tissue composition changes with lymphedema using dual-energy X-ray absorptiometry (DXA), and to determine the relationships between the DXA-determined tissue volumes and the clinical outcomes determined by perometry and bioimpedance spectroscopy. METHODS AND RESULTS: Fifty-six women with secondary lymphedema and 44 women without a history of breast cancer or lymphedema underwent measurement of their upper limbs with DXA, perometry, and bioimpedance spectroscopy. Whether the affected side was the dominant or nondominant arm influenced inter-limb tissue volumes differences (F=16.31 to 35.14; all p<0.001) and interacted with the severity of lymphedema (F=3.22 to 11.07; all p<0.05). In the control group, the dominant limb had more lean tissue but less fat than the nondominant limb. In the lymphedema group, increases in fat in the affected arm were not related to generalized increases in whole body adiposity when the dominant arm was affected. Perometry-measured volumes and BIS ratios were moderately to highly correlated with inter-limb fat, volume, and total tissue differences found by DXA (r=0.39 to 0.86). CONCLUSIONS: The direction and magnitude of limb composition changes in those with lymphedema are impacted by whether the affected side is the dominant or nondominant limb, as well as the severity of the condition. The stage of tissue composition change may impact on the diagnosis and monitoring as well as treatment of secondary lymphedema.

Increased bone mineral density in Aboriginal and Torres Strait Islander Australians: impact of body composition differences.

Bone mineral density (BMD) has been reported to be both higher and lower in Indigenous women from different populations. Body composition data have been reported for Indigenous Australians, but there are few published BMD data in this population. We assessed BMD in 161 Indigenous Australians, identified as Aboriginal (n=70), Torres Strait Islander (n=68) or both (n=23). BMD measurements were made on Norland-XR46 (n=107) and Hologic (n=90) dual-energy X-ray absorptiometry (DXA) machines. Norland BMD and body composition measurements in these individuals, and also in 36 Caucasian Australians, were converted to equivalent Hologic BMD (BMD(H)) and body composition measurements for comparison. Femoral neck (FN) and lumbar spine Z-scores were high in Indigenous participants (mean FN Z-score: Indigenous men +0.98, p<0.0001 vs. mean zero; Indigenous women +0.82, p<0.0001 vs. mean zero). FN BMD(H) was higher in Aboriginal and/or Torres Strait Islander than Caucasian participants, after adjusting for age, gender, diabetes and height and remained higher in men after addition of lean mass to the model. We conclude that FN BMD is higher in Aboriginal and/or Torres Strait Islander Australians than Caucasian Australian reference ranges and these differences still remained significant in men after adjustment for lean mass. It remains to be seen whether these BMD differences translate to differences in fracture rates.