Dual-Energy X-Ray Absorptiometry (DEXA)

Dual-energy X-ray absorptiometry (DEXA) is the latest, most accurate, and most expensive means of determining body composition, and it is generally considered the current gold standard for this purpose. The information you can derive from a full-body scan on an athlete is invaluable, including bone density; body fat percentage; lean body mass; fat mass; and the distribution of fat and lean tissue in the arms, trunk, and legs. DEXA output even provides the differences in lean mass and fat mass between the left and right sides. This information can be particularly important for athletes who wish to develop symmetrical bodies or who, because of the nature of the sport, need to produce the same muscular power in each leg or in each arm.

DEXA works by passing two X-ray beams through the subject and measuring the amount of X ray absorbed by the tissue it has passed through. One beam is high intensity and one is low intensity, so the relative absorbance of each beam is an indication of the density of the tissue it has passed through. The higher the tissue density, the greater the reduction in X-ray intensity. Don't be frightened by all this talk of X-ray beams passing through your body. In fact, the amount of radiation energy that is used with DEXA is extremely small. You would need to have approximately 800 full-body DEXA scans before being exposed to the same amount of radiation received from one standard chest X ray. In fact, the level of radiation is so low that DEXA is approved by the FDA as a screening device to predict body composition. Usually, X-ray devices are reserved as diagnostic instruments because of the amount of radiation they impart, but not so for DEXA.

The procedure for DEXA, which was originally developed to determine the density of bone, couldn't be easier. The subject lies on the DEXA table for approximately 20 minutes, and the pencil-beam X rays pass through the subject and are interpreted by a mechanical arm above the subject. Because metal has such a high density, the subject is asked to remove all jewelry and must wear clothing that contains no metal. The resultant value is translated into a density value for bone, lean, and fat tissue. Because the density values are derived from a direct assessment of tissue density, this is as close as we can get to directly assessing tissue density (short of surgery). If you can find a lab with DEXA, the usual cost for a full-body scan is somewhere between $100 and $250.