What is a DEXA Scan?
DEXA stands for dual-energy X-ray absorptiometry. The official abbreviation is DXA, but most people say DEXA and it is referring to the same test. DEXA scans are the most reliable form of measuring body composition. It provides much more reliable measurements than outdated metrics like BMI. DEXA scans are far more beneficial than a scale, which don’t show nearly close to the big picture.
DEXA scans were initially used for testing bone mineral density to detect signs of bone conditions such as osteoporosis and osteopenia. However, these scans are very versatile. Not only can DEXA scans tell you your bone mineral density, they can determine your body composition. This includes total mass, fat mass, lean mass, and area.
During a DEXA scan, you lay on your back for about 7 minutes while you are scanned by the machine, which is represented by the header image of this post. In this article, we’ll be discussing scan results from DEXA Boston using a Lunar Prodigy DEXA scan machine created by GE Healthcare.
Bone Mineral Density (BMD)
One thing that a DEXA scan measures- and the reason DEXA scans were founded- is to analyze bone mineral density (BMD). BMD Is measured in grams per centimeter squared. the T-score and Z-score show your relative BMD to young adults and people of the same age respectively. Some tests may even do the math for you and tell you what percentile you fall under for BMD. For example, a 25 year old woman with a BMD(g/cm^2) of 1.273 will have a T-score of 1.9, Z-score of 2.1, and percentile of 98. This means that she would have more bone mineral density than 98% of the population and have a very low risk of osteoporosis and fractures.
Low BMD, especially in the hip and spine, can indicate signs of bone disorders such as osteopenia and osteoporosis, which can put you at higher risk for fractures[1]. DEXA scans can break down your BMD by body part such as: head, arms, leg, trunk, ribs, spine, and pelvis/hip. Some natural ways to increase or maintain BMD over time are resistance training, as well as eating more calcium, vitamin D, and protein.
Body Composition
DEXA scans give you the big picture of your fat and lean mass. DEXA scans will tell you your overall body fat percentage. This is far different from BMI; BMI is an outdated metric based solely on height and weight without considering any other factors[2]. Body fat percentage, sometimes abbreviated as BFP, is the ratio of fat and lean mass in your body. Someone, perhaps a powerlifter, could have a BMI that considers them “obese” yet have a normal real body fat percentage. This can only be determined by a scan and not a scale.
Not only will a DEXA scan show you your total body composition, it can also break it down into composition by body part. Typically, these body parts will be on the scan: Arms, legs, and trunk. Many skins even differentiate between your right and left arm, and your right and left leg. this will help identify any potential muscle imbalances.
Specifically, the report will often show these metrics for composition: total mass, fat mass, lean mass, area, and BMC. Total mass is the weight in pounds of the body part. Fat mass is the weight of fat. Lean mass is all of your weight that is not fat, including muscle and water. Area is measured by cubic centimeters.
VAT
VAT stands for visceral adipose tissue, also called visceral fat. The ability to distinguish VAT is one of the things that sets DEXA scans apart as one of the most useful body composition methods out there. VAT is a type of fat that is stored around vital organs. An excess of VAT increases your risk for diseases like diabetes and metabolic syndrome[3]. A good visceral fat measurement is usually regarded as less than 1 pound.
Although there is a correlation between overall high body fat percentage and high VAT, this isn’t always the case. A heavier person who trains regularly and eats clean may very well have a lower VAT than a small person who rarely exercises and often eats candy.
Android to Gynoid Ratio
The android to gynoid (A/G) ratio portion of a DEXA scan is also considered hip-to-waist ratio. Unlike a typical hip-to-waist ratio measurement, it uses body fat percentage for the hip region (gynoid) and waist region (android) instead of circumference. For example, someone with a gynoid fat percentage reading of 37.2% and android fat percentage reading of 30.7% will have an A/G ratio of 0.82. This number should be under 1, signifying the waist is less fatty than the hips. The ideal ratio is less than 0.8 for women and 1.0 for men.
Resting Metabolic Rate (RMR)
The resting metabolic rate (RMR) section of a DEXA scan shows you the amount of calories it would take to support your organs and normal bodily functions at rest[4]. This is not to be mistaken for total daily energy expenditure (TDEE) which is the number of calories it takes to maintain your weight with all factors considered. RMR is the number of calories to support your essential functions like breathing, if you did absolutely nothing but rest.
Relative Skeletal Muscle Index (RSMI)
A relative skeletal muscle index (RSMI) is measured by taking the sum of your arm and leg muscle weight in kilograms and dividing it by your height in meters. The higher the number, the stronger you are generally considered to be. A number over 7.26 for men and 5.45 for women is considered healthy[5]. Numbers lower than this can signal muscle atrophy and is a sign of sarcopenia (loss of muscle, usually associated with aging). RSMI can be maintained or improved by performing regular resistance training exercises, and eating more protein.
Conclusion
A DEXA scan is used for two primary goals. The first is to assess bone mineral density (BMD). Low BMD raises a red flag for potential bone disorders such as osteopenia and osteoporosis, which increase fracture risk. The second goal of a DEXA scan is to evaluate body composition, which includes body fat percentage, visceral fat, and muscle mass.
As you can see, DEXA scans are not only helpful for diagnostic and weight loss goals, but also for general health. They can even be used to see if a bulk is realistically going as planned; how much of your weight gain is muscle? DEXA can tell you. Regardless of your goals, investing in a DEXA scan will give you a good picture of your overall physical fitness.
References
[1] National Institute of Arthritis and Musculoskeletal and Skin Diseases. (2025). Bone mineral density tests: What the numbers mean. https://www.niams.nih.gov/health-topics/bone-mineral-density-tests-what-numbers-mean
[2] Nordqvist, C. (2022). Why BMI is inaccurate and misleading. https://www.medicalnewstoday.com/articles/265215
[3] Chen, W., Wilson, J. L., Khaksari, M., Cowley, M. A., & Enriori, P. J. (2012). Abdominal fat analyzed by DEXA scan reflects visceral body fat and improves the phenotype description and the assessment of metabolic risk in mice. American Journal of Physiology-Endocrinology and Metabolism, 303(5), E623–E633. https://doi.org/10.1152/ajpendo.00078.2012
[4] Rosenbloom, C. RMR: What Is resting metabolic rate? (2024) https://www.verywellfit.com/metabolism-facts-101-3495605#:~:text=What%20Is%20RMR?,3
[5] Baumgartner, R. N., Koehler, K. M., Gallagher, D., Romero, L., Heymsfield, S. B., Ross, R. R., Garry, P. J., & Lindeman, R. D. (1998). Epidemiology of sarcopenia among the elderly in New Mexico. American Journal of Epidemiology, 147(8), 755–763.