What does a DEXA scan show you, and can it estimate body fat accurately?

Martha M. Henze, MPH, MS, RDN - Registered Dietitian Nutritionist and Global Public Health Epidemiologist

What is a DEXA scan, and what does it show? It gives you more info than the average bathroom scale, for starters. Read on to learn how DEXA results can help you assess your body fat and muscle mass.

What is a DEXA machine, and what does a DEXA scan show you about your body composition?

DEXA stands for dual x-ray absorptiometry. Originally used in medical centers to measure bone mineral density, the DEXA scan indicates if you are at higher risk for a fracture due to weak bones. A DEXA scan can also differentiate between fat and muscle tissue, providing a comprehensive analysis of your total body composition. That's the focus we dive deeper into here.

Accuracy of a DEXA scan for body fat

When it comes to estimating body fat, a DEXA scan is the gold standard, boasting an error rate as low as 1-2%. Other body fat tests such as bioelectrical impedance analysis and skinfold caliper testing may result in a 3-5% error rate even under optimal testing conditions. Another accurate body composition test, underwater weighing, averages an error rate of 1-3%. However, it requires submerging in water and is not appropriate for certain populations.

How is a DEXA scan performed?

The test takes place in a medical facility by trained technicians. It is a non-invasive, painless procedure that lasts about 20 minutes. A radiology technician guides you through the process. They help you get situated in a hospital gown and comfortable lying on your back on an x-ray table. Once the test starts, you must remain completely still while the technician moves a large scanning arm over your body. The test is very safe with minimal radiation exposure.

When to get a DEXA scan?

If you are just starting a new exercise program, you may consider this test at the beginning of your program. Then after 90 days, get another scan to see how your body composition is changing. Since muscle weighs more than fat, the scale may show that your weight is increasing. But don't worry! You now have a lower percentage of body fat, and that means progress toward a healthier body.

Pros and cons of a DEXA scan for body composition testing

Pros

• Reliable, precise, and fast
• Only body composition tool that looks at three components and provides you with:
  • Percentage of body fat
  • Percentage of lean mass (muscles)
  • Bone mineral content to test for risk of osteopenia and osteoporosis
• Regional analysis: breakdown of body fat and lean mass in five regions of the body
  • Arms
  • Trunk
  • Belly
  • Hips
  • Legs
• Compares the right and left sides of the body looking for imbalances in muscle development due to injury or usage

Cons

• Depending on your location and insurance, prices will vary and may be quite high Researching the cost up-front will prevent a surprise bill
• Not recommended for pregnant women

What does a DEXA scan show that a bathroom scale doesn't? Plenty. Will it give you news you can use or more measurements that just stress you out? That depends on whether you want results to help propel you toward your goals or not. Either way, this painless test can show you what you are made of!

Reviewed and updated by Joanna Kriehn MS, RDN, CDCES, on June 30, 2021.

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