This video about how a full body dual-energy x-ray absorptiometry (DEXA) scan works as the best way to measure body composition. However, few clinics provide it since they only use DEXA to measure bone density in the lower back and pelvis. It required special calibration for a full body scan. Talk to your doctor is he can find a local clinic that can do a full body DEXA scan. Your insurance may not pay for it. Out of pocket cost may be close to $200. You only need to do it every 2-3 years for bone density if you are over 50 and HIV+. If you are a bodybuilder that expects dramatic body changes in a few months, then every 6 months to a year would be OK. The amount of X ray radiation you are exposed to is equivalent to your exposure in a transatlantic flight.