Total and regional body volumes derived from dual-energy X-ray absorptiometry output.

Total body volume is an important health metric used to measure body density, shape, and multicompartmental body composition but is currently only available through underwater weighing or air displacement plethysmography (ADP). The objective of this investigation was to derive an accurate body volume from dual-energy X-ray absorptiometry (DXA)-reported measures for advanced body composition models. Volunteers received a whole body DXA scan and an ADP measure at baseline (N = 25) and 6 mo (N = 22). Baseline measures were used to calibrate body volume from the reported DXA masses of fat, lean, and bone mineral content. A second population (N = 385) from the National Health and Nutrition Examination Survey was used to estimate the test-retest precision of regional (arms, legs, head, and trunk) and total body volumes. Overall, we found that DXA-volume was highly correlated to ADP-volume (R² = 0.99). The 6-mo change in total DXA-volume was highly correlated to change in ADP-volume (R² = 0.98). The root mean square percent coefficient of variation precision of DXA-volume measures ranged from 1.1% (total) to 3.2% (head). We conclude that the DXA-volume method can measure body volume accurately and precisely, can be used in body composition models, could be an independent health indicator, and is useful as a prospective or retrospective biomarker of body composition.

Hip Fractures Risk in Older Men and Women Associated With DXA-Derived Measures of Thigh Subcutaneous Fat Thickness, Cross-Sectional Muscle Area, and Muscle Density.

Mid-thigh cross-sectional muscle area (CSA), muscle attenuation, and greater trochanter soft tissue thickness have been shown to be independent risk factors of hip fracture. Our aim was to determine whether muscle and adipose tissue measures derived from dual-energy X-ray absorptiometry (DXA) scans would have a similar risk association as those measured using other imaging methods. Using a case-cohort study design, we identified 169 incident hip fracture cases over an average of 13.5 years among participants from the Health ABC Study, a prospective study of 3075 individuals initially aged 70 to 79 years. We modeled the thigh 3D geometry and compared DXA and computed tomography (CT) measures. DXA-derived thigh CSA, muscle attenuation, and subcutaneous fat thickness were found to be highly correlated to their CT counterparts (Pearson's r = 0.82, 0.45, and 0.91, respectively; p < 0.05). The fracture risk of men and women were calculated separately. We found that decreased subcutaneous fat, CT thigh muscle attenuation, and appendicular lean mass by height squared (ALM/Ht(2)) were associated with fracture risk in men; hazard ratios (HR) = 1.44 (1.02, 2.02), 1.40 (1.05, 1.85), and 0.58 (0.36, 0.91), respectively, after adjusting for age, race, clinical site, body mass index (BMI), chronic disease, hip bone mineral density (BMD), self-reported health, alcohol use, smoking status, education, physical activity, and cognitive function. In a similar model for women, only decreases in subcutaneous fat and DXA CSA were associated with hip fracture risk; HR = 1.39 (1.07, 1.82) and 0.78 (0.62, 0.97), respectively. Men with a high ALM/Ht(2) and low subcutaneous fat thickness had greater than 8 times higher risk for hip fracture compared with those with low ALM/Ht(2) and high subcutaneous fat. In women, ALM/Ht(2) did not improve the model when subcutaneous fat was included. We conclude that the DXA-derived subcutaneous fat thickness is a strong marker for hip fracture risk in both men and women, especially in men with high ALM/Ht(2).

Ratio of trunk to leg volume as a new body shape metric for diabetes and mortality.

BACKGROUND: Body shape is a known risk factor for diabetes and mortality, but the methods estimating body shape, BMI and waist circumference are crude. We determined whether a novel body shape measure, trunk to leg volume ratio, was independently associated with diabetes and mortality. METHODS: Data from the National Health and Nutritional Examination Survey 1999-2004, a study representative of the US population, were used to generate dual-energy X-ray absorptiometry-derived trunk to leg volume ratio and determine its associations to diabetes, metabolic covariates, and mortality by BMI category, gender, and race/ethnicity group. RESULTS: The prevalence of pre-diabetes and diabetes increased with age, BMI, triglycerides, blood pressure, and decreased HDL level. After adjusting for covariates, the corresponding fourth to first quartile trunk to leg volume ratio odds ratios (OR) were 6.8 (95% confidence interval [CI], 4.9-9.6) for diabetes, 3.9 (95% CI, 3.0-5.2) for high triglycerides, 1.8 (95% CI, 1.6-2.1) for high blood pressure, 3.0 (95% CI, 2.4-3.8) for low HDL, 3.6 (95% CI, 2.8-4.7) for metabolic syndrome, and 1.76 (95% CI, 1.20-2.60) for mortality. Additionally, trunk to leg volume ratio was the strongest independent measure associated with diabetes (P<0.001), even after adjusting for BMI and waist circumference. Even among those with normal BMI, those in the highest quartile of trunk to leg volume ratio had a higher likelihood of death (5.5%) than those in the lowest quartile (0.2%). Overall, trunk to leg volume ratio is driven by competing mechanisms of changing adiposity and lean mass. CONCLUSIONS: A high ratio of trunk to leg volume showed a strong association to diabetes and mortality that was independent of total and regional fat distributions. This novel body shape measure provides additional information regarding central adiposity and appendicular wasting to better stratify individuals at risk for diabetes and mortality, even among those with normal BMI.

Improved 4-compartment body-composition model for a clinically accessible measure of total body protein.

BACKGROUND: Muscle wasting is a consequence of many primary conditions including sarcopenia, cachexia, osteoporosis, HIV/AIDS, and chronic kidney disease. Unfortunately, there is not a clinically accessible method to measure total body protein, which is the functional mass of muscle. OBJECTIVE: We sought to derive a simple method to measure total body protein by using dual-energy X-ray absorptiometry (DXA) and bioimpedance analysis (BIA). DESIGN: We retrospectively analyzed a clinical convenience sample of individuals with numerous metabolic conditions from the Monash Medical Centre, Melbourne, Australia, who had a concurrent protein measure by using neutron activation analysis-derived protein (NAA-TBPro), water measure by using BIA, and whole-body DXA scan. The study was split into calibration and validation data sets by using simple random sampling stratified by sex, BMI category, and age decade. We generated a protein estimate direct-calibration protein (DC-TBPro) derived from BIA water, bone mass, and body volume. We compared NAA-TBPro with DC-TBPro and 2 protein estimates from the literature, one that used the DC-TBPro equation with fixed coefficients [4-compartment Lohman method for analysis of total body protein (4CL-TBPro)] and another that used fat-free mass, age, and sex [Wang equation-derived protein (W-TBPro)]. RESULTS: A total of 187 participants [119 women; mean (±SD) age: 37.0 ± 15.4 y; mean (±SD) BMI (in kg/m(2)) 24.5 ± 7.7] were included. When plotted against NAA-TBPro, DC-TBPro had the highest correlation [coefficient of determination (R(2)) = 0.87], lowest root mean squared error (RMSE; 0.87 kg), and fewest outliers compared with 4CL-TBPro (R(2) = 0.75; RMSE = 1.22 kg) and W-TBPro (R(2) = 0.80; RMSE = 1.10 kg). CONCLUSIONS: A simple method to measure total body protein by using a DXA system and BIA unit was developed and compared with NAA as proof of principle. With additional validation, this method could provide a clinically useful way to monitor muscle-wasting conditions.

Dual-energy X-ray absorptiometry-based body volume measurement for 4-compartment body composition.

BACKGROUND: Total body volume (TBV), with the exclusion of internal air voids, is necessary to quantify body composition in Lohman's 4-compartment (4C) model. OBJECTIVE: This investigation sought to derive a novel, TBV measure with the use of only dual-energy X-ray absorptiometry (DXA) attenuation values for use in Lohman's 4C body composition model. DESIGN: Pixel-specific masses and volumes were calculated from low- and high-energy attenuation values with the use of first principle conversions of mass attenuation coefficients. Pixel masses and volumes were summed to derive body mass and total body volume. As proof of concept, 11 participants were recruited to have 4C measures taken: DXA, air-displacement plethysmography (ADP), and total body water (TBW). TBV measures with the use of only DXA (DXA-volume) and ADP-volume measures were compared for each participant. To see how body composition estimates were affected by these 2 methods, we used Lohman's 4C model to quantify percentage fat measures for each participant and compared them with conventional DXA measures. RESULTS: DXA-volume and ADP-volume measures were highly correlated (R(2) = 0.99) and showed no statistically significant bias. Percentage fat by DXA volume was highly correlated with ADP-volume percentage fat measures and DXA software-reported percentage fat measures (R(2) = 0.96 and R(2) = 0.98, respectively) but were slightly biased. CONCLUSIONS: A novel method to calculate TBV with the use of a clinical DXA system was developed, compared against ADP as proof of principle, and used in Lohman's 4C body composition model. The DXA-volume approach eliminates many of the inherent inaccuracies associated with displacement measures for volume and, if validated in larger groups of participants, would simplify the acquisition of 4C body composition to a single DXA scan and TBW measure.