Body Mass Index (BMI) is still used as the leading measure of being overweight, but the calculation, based on height and weight, can be misleading. In fact, a study found that nearly 20% of women with normal BMI carried excess fat, visible on the DEXA scan, results in misleading inferences about a person’s health risk.

DEXA or Dual-energy X-ray absorptiometry was originally develop to measure bone mineral density, and in fact it is the gold standard method used for the diagnosis of osteoporosis. But this incredible technology can also be used to analyse the body and improve your health!

Using an enhanced form of x-ray technology, in addition to bone mineral density, it can measure your total body composition with the highest level of accuracy. This means that DEXA will give you a detailed breakdown of your body mass, from the weight of your bones to the total fat and lean tissue. Emerging evidence shows that a DEXA scan is highly accurate compared with most other methods for determining body composition and it is also an excellent tool for tracking changes in muscle and fat mass over time.

Used in combination the scans are certainly more accurate than BMI, as results can actually show your progress for muscle development and fat loss. The scan takes 5 minutes, and it generates a detailed report calculated instantly, showing the individual breakdown of bone, fat and lean tissues - including organs and muscle.

Along with information about the body as a whole, “the DXA report shows the amount of fat and lean tissue in each body part, such as the right arm or left leg—information that can be helpful for athletes to see if an injured limb is regaining muscle,” says Dr. Shepherd.  In addition, the exam estimates for the amount of visceral fat in patients, a measure that can help predict risk for diabetes and heart disease.

At UCSF we are currently offering DXA scans for bone density and body composition at the brand new UCSF Imaging Center at Montgomery Street, located in downtown San Francisco, and the UCSF Orthopaedic Institute Imaging Center at Mission Bay. To get a DXA scan at these locations, please see a physician and request a referral.

Additionally, the Body Composition, Exercise Physiology, and Energy Metabolism lab is a partnership with CTSI, Millberry Union Fitness Center, and UCSF Radiology. The lab performs DXA whole body composition exams for self-assessment of body composition without a prescription or referral. This is for individuals starting a weight reduction, strength building, or fitness program who want to monitor their progress with an accurate measure of body composition.


Lambert, Bradley & Oliver, Jonathan & Kaats, Gilbert & S Green, John & Martin, Steven & F Crouse, Stephen. (2012). DEXA or BMI: Clinical Considerations for Evaluating Obesity in Collegiate Division I-A American Football Athletes. Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine. 22. 436-8. 10.1097/JSM.0b013e31825d5d65.