DEXA Body Composition Scan

A DEXA scan uses two low-energy X-ray beams to measure how much of your body is fat, how much is lean tissue, and how much is bone — and where each is distributed. You lie still on a padded table for about 10 minutes while the scanner passes over you. There's no discomfort and no contrast injection.

Because the scanner can distinguish bone, fat, and lean tissue separately, it produces a regional breakdown — arms, legs, trunk, android (waist), gynoid (hips) — along with whole-body totals. It also estimates visceral adipose tissue, the metabolically dangerous fat surrounding your organs.

Radiation exposure is roughly equivalent to one day of natural background radiation — far less than a chest X-ray.

Your scale tells you your weight. Your BMI tells you whether your weight is reasonable for your height. Neither tells you what you're actually made of — which is what matters for metabolic health, longevity, injury risk, and physical function.

Lean muscle mass is one of the strongest predictors of long-term mortality, fall risk, and the ability to recover from illness or injury. Visceral fat is independently associated with cardiovascular disease, insulin resistance, and several cancers — even in people whose total weight looks fine.

Bone density measured at the hip and spine is the standard for diagnosing osteopenia and osteoporosis. Catching bone loss in your 40s or 50s gives you decades to do something about it; catching it after a fracture is far less useful.

• Total and regional fat mass and percentage
• Total and regional lean mass (skeletal muscle index)
• Visceral adipose tissue (VAT) estimate
• Bone mineral density at the hip and lumbar spine, with T-scores and Z-scores
• Android-to-gynoid ratio — a marker of central fat distribution

• Anyone who wants to know what their body is actually made of, not just what it weighs.
• Patients losing weight who want to confirm they're losing fat rather than muscle.
• Patients building muscle who want to see hypertrophy reflected accurately.
• Adults over 40, especially women near and after menopause, who want a baseline bone density scan.
• Anyone with a family history of osteoporosis or who has been on long-term steroids, certain hormonal therapies, or other medications affecting bone.

• Plan on about 20 minutes total at the imaging facility, including check-in and a 10-minute scan.
• Wear loose clothing without metal — no zippers, snaps, or underwire bras over the scan field. Many facilities provide a gown.
• You'll lie on your back on a padded table while the scanner arm moves slowly above you. There's no enclosed tube and no noise to speak of.
• Do not take calcium supplements within 24 hours of the scan — they can interfere with bone density readings.

We look at your numbers in three layers: where you stand against age- and sex-matched reference ranges, what the regional distribution suggests about metabolic risk, and how the picture changes from scan to scan.

For body composition, the goals are usually some combination of lower visceral fat and higher lean mass — not a single 'right' weight. For bone density, T-scores below -1 trigger a deeper conversation about prevention; below -2.5 is osteoporosis.

Most patients repeat a scan every 12 to 18 months. That's frequent enough to detect meaningful change and infrequent enough to avoid noise.

1. Shepherd JA, Ng BK, Sommer MJ, Heymsfield SB. Body composition by DXA. Bone. 2017;104:101-105.
2. Oh JH, et al. Comparison of DXA and CT for regional fat and lean mass measurement. Br J Radiol. 2025.Found DEXA closely tracks full-body CT, particularly in the limbs, supporting its use as a practical body-composition tool.
3. UK Biobank cross-sectional and longitudinal DXA vs. MRI comparison. Commun Med (Nature). 2026.Both methods track fat similarly, but DXA can overestimate muscle mass and under-detect muscle loss over time compared with MRI — a nuance worth noting for longitudinal tracking.