Abstract
PURPOSE: Increasing evidence suggests that abdominal obesity may be a better predictor of disease risk than total fatness. This study sought to determine how obesity and fat distribution measured by readily available anthropometric and dual-energy x-ray absorptiometry (DXA) methods is related to abdominal obesity assessed by magnetic resonance imaging (MRI).
METHODS: Men (n = 43) and women (n = 47), ages 55 to 75 years, were assessed for body mass index, waist-to-hip ratio, waist circumference, and skin folds by anthropometric methods; for percentage of body fat by DXA; and for abdominal total, subcutaneous, and visceral fat by MRI.
RESULTS: In stepwise regression models, the waist-to-hip ratio explained 50% of the variance in abdominal visceral fat among men (P < .01), and body mass index explained an additional 6% of the variance (P < .01). Among women, waist circumference was the only independent correlate of abdominal visceral fat, accounting for 52% of the variance (P < .01). Among men, the percentage of body fat was the only independent correlate of abdominal subcutaneous fat, explaining 65% of the variance (P < .01). Among women, the percentage of body fat explained 77% of the variance in abdominal subcutaneous fat and body mass index explained an additional 3% (P < .01).
CONCLUSIONS: Obesity and body composition obtained by readily available anthropometric methods and DXA provide informative estimates of abdominal obesity assessed by MRI imaging.
An accurate clinical assessment of health risk for cardiovascular and metabolic disease should include an estimate of body fat distribution. Abdominal obesity confers a significant risk to health, 1 and is associated with insulin resistance, 2,3 hypertriglyceridemia, low levels of plasma high-density lipoprotein-cholesterol, hypertension, and reduced fibrinolytic activity. 4 Increasing evidence suggests that the deeper layers of abdominal fat, particularly the visceral component, contribute independently to the metabolic and cardiovascular complications of obesity. 3,5-7 Abdominal obesity also increases with aging, 8-10 and it may be that fat distribution is a mediator of the increased health risk as individuals get older. 6
The application of imaging technologies in obesity research has allowed for precise and direct measurement of abdominal obesity. Magnetic resonance imaging (MRI) is an accurate and precise technique for evaluating adipose tissue mass in subcutaneous and intraabdominal compartments, 11,12 and its validity has been established in human autopsy studies. 13,14 Nevertheless, MRI for assessing body composition is not used in the clinical setting. Instead, body composition and fat distribution typically are estimated by anthropometric measures, which can be obtained inexpensively with relatively simple instrumentation. Dual-energy x-ray absorptiometry (DXA), commonly performed to assess osteoporosis risk in older persons, also can provide accurate measurement of body fat mass. Limited data for younger obese adults suggest the potential utility of anthropometric measures used to predict visceral fat. 15,16 Even less data are available for older persons on the quantification of abdominal obesity by MRI and its relations with anthropometric and DXA measures of body composition. The current study determined the extent to which several readily available anthropometric and DXA measures of obesity and fat distribution are associated with measures of abdominal subcutaneous and visceral fat by MRI and can describe patterns of body fat and distribution in older men and women.