Prediction of body composition from spine and hip bone densitometry.

Body mass index (BMI) is used to assess overweight and obesity, but it does not account for the distribution or composition of excess weight. Dual-energy X-ray absorptiometry (DXA) is widely used for the assessment of osteoporosis. We hypothesized that measures of regional fat tissue composition from spine and hip DXA done for osteoporosis assessment could be used to estimate body composition more accurately than with BMI. We identified 427 adult patients who underwent DXA evaluation of the lumbar spine, hip, and whole body at the same visit. The population was randomly divided into 2 equal-sized subgroups: one used to derive prediction equations for whole-body fat tissue, whole-body lean tissue, and trunk fat tissue, and the other for independent validation. The estimates were compared with the actual measurements from the whole-body scans. In all analyses, prediction using the regional DXA scans outperformed prediction using BMI or its component variables, height and weight. When the predicted and actual measurements were compared in the validation cohort, regression slopes did not differ significantly from unity and the intercepts did not differ significantly from zero. We conclude that regional DXA scans of the spine and hip can be used to accurately measure body composition. Further research is needed to see whether these measures can in turn predict the metabolic complications associated with overweight and obesity.