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(1)
DXA scans for body composition can measure percent body fat, android fat, visceral fat, lean body mass, and bone mineral density.
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(2)
Lean body mass is defined as total body mass less nonessential or storage adipose tissue (i.e., water, protein, bone, essential body fat) and has wide variance among individuals, depending on an individual's mass of muscle, organs, and bone, which in turn is largely dependent on height, gender, genetics, nutrition, physical activity and overall health.
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(3)
An increase in body mass (lean body mass or adipose tissue mass) increases resting energy expenditure.
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(4)
The Obesity Medicine Association has established cutoff points for percent body fat (% BF) for women: pre-obesity = 30 – 34% BF and obesity ≥ 35 BF%; for men pre-obesity = 25 – 29% BF and obesity ≥ 30 BF%. The American Council on Exercise Classification has no categorization for pre-obesity or overweight, and defines obesity as ≥ 32% BF for women and ≥ 25% BF for men.
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(5)
Android and visceral adiposity correlate with increased CVD risk. Epicardial fat has direct adiposopathic potential to adversely affect the heart. Epicardial and visceral adipose tissue share the same mesodermal embryonic origin, directly correlate with one another; both are associated with increased coronary artery calcification. Adipocyte hypertrophy and adipose tissue expansion may result in adiposopathic endocrinopathies and immunopathies (e.g., hormonal and pro-inflammatory responses from adipocyte hypertrophy and adipose tissue accumulation) [153, 154] that can directly contribute to CVD (i.e., epicardial proinflammatory signaling) and indirectly contribute to CVD (i.e., promotion of insulin resistance, high blood sugar, high blood pressure, and high blood lipids – all CVD risk factors).
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(6)
Percent body fat by DXA measures may not always correlate well with other percent body fat assessment devices – sometimes having % BF values 10% higher or more.
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(7)
For most DXA measures, the android region is defined as the area between the ribs and the pelvis; visceral fat is the intraabdominal fat surrounding body organs.
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(8)
While generally accurate for populations, body mass index (kilogram weight per meter squared height or kg/m2) may not be accurate in assessing body fat in individuals, especially those with increased muscle mass or sarcopenia. While percent body fat more accurately reflects body composition, the greatest support in correlating body fat to CVD is central adiposity (measures of waist circumference), as well as android and visceral fat. According to the Obesity Medicine Association, “optimal” android fat is < 3 pounds (~1400 grams) and optimal visceral fat is < 1 pound (~500 grams). Within individuals (particularly women) total percent body fat may not reflect android or visceral fat measures. Some women with increased overall percent body fat may have no detectable visceral fat via DXA; the average rate of onset of CVD in women is ~ 10 years later than men. [1, 2]
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(9)
Not all DXA facilities perform body composition (i.e., many DXA scans are performed exclusively for bone mineral density). Not all DXA can distinguish between visceral and subcutaneous fat, nor accomodate patients with higher body mass index (i.e., ≥ 350 pounds).
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(10)
The addition of a waist circumference to other non-DXA measures of percent body fat (e.g., air displacement plethysmography, bioelectrical impedance, underwater weighing densitometry) may provide complementary prognostic information regarding CVD risk.
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