What it means
Dual-energy X-ray absorptiometry passes two X-ray energies through the body and uses the difference in absorption to separate bone mineral, lean tissue and fat, region by region. It was developed for bone density and is still the diagnostic test for osteoporosis; the whole-body version adds appendicular lean mass (arms and legs — the sarcopenia measure), total and regional fat, and an estimate of visceral fat.
The radiation dose is about 1–5 microsieverts, less than a day of natural background.
Why it matters for longevity
Muscle mass, visceral fat and bone density are three of the strongest predictors of healthspan, and none is visible on a scale or a BMI. A DEXA converts "lose fat, keep muscle" from a hope into two numbers that can be checked every few months.
What the evidence says
DEXA lean-mass measurement agrees closely with MRI and the four-compartment research model; precision error for repeat scans is about 1–2% for lean mass and total fat, which means a real change of 1 kg of muscle is detectable. The visceral-fat estimate correlates well with CT (r ≈ 0.9) in validation studies.
For bone, DEXA T-scores define osteopenia (−1 to −2.5) and osteoporosis (below −2.5), and predict fracture. For muscle, the EWGSOP2 sarcopenia definition uses DEXA appendicular lean mass divided by height squared: under 7.0 kg/m² in men and 5.5 in women.
How to measure or use it
- Book a whole-body scan with visceral-fat reporting; same machine, same time of day, similar hydration and fasting state each time.
- Repeat every 3–6 months when actively changing body composition, yearly otherwise; bone every 1–2 years after 50.
- Read: appendicular lean mass index, total body-fat percentage, VAT in grams, and the bone T-score. Pair with grip strength, since mass without strength misses half the picture.
Related
- Muscle mass and ageing — what the lean-mass numbers should be
- Baseline labs — where a DEXA sits in the baseline
- The recomposition protocol — DEXA as the tracking tool
Frequently asked questions
How accurate is a DEXA for body fat?
Precision on repeat scans is about 1–2%, better than any consumer method. Absolute values vary between machine makers, so always compare on the same scanner.
Is the radiation a concern?
No. A whole-body scan is 1–5 microsieverts, less than a day of background radiation or a short flight.
How often should I scan?
Every 3–6 months during an active fat-loss or muscle-gain phase; yearly for maintenance; bone density every 1–2 years after 50.
Want this applied to your own numbers?
Fifteen minutes of intake, your labs, a human-reviewed protocol within about 24 hours, three documents, a free coach call and check-ins through the cycle. €399, follow-up included.
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