Encyclopedia entry

DXA body composition

Dual-energy X-ray absorptiometry (DXA, sometimes DEXA) is a low-dose X-ray scan that measures body composition with high precision: total and regional fat mass, total and regional lean mass, bone mineral content. It is the laboratory gold standard against which BMI, bioimpedance, skinfold calipers, and waist-circumference methods are validated. UK longevity clinics increasingly include DXA in baseline assessments.

What a DXA scan reports

• · Total fat mass and body fat percentage.
• · Visceral adipose tissue (VAT) estimate in some DXA models.
• · Total lean mass (skeletal muscle plus organs minus bone).
• · Appendicular lean mass index (ALMI): lean mass in arms and legs, the marker for sarcopenia.
• · Bone mineral density: T-score (osteoporosis screen) and Z-score.
• · Regional split: trunk, arms, legs, android vs gynoid.

Radiation dose

A whole-body DXA scan delivers approximately 0.001 to 0.005 millisieverts (mSv) of ionising radiation, comparable to a few hours of natural background radiation or a transatlantic flight. Vastly lower than CT (5 to 15 mSv) or a chest X-ray (0.1 mSv). DXA is not contraindicated for routine annual screening.

UK availability

DXA is widely available in UK longevity clinics (Hooke includes it as standard; Echelon Health offers as add-on). Private cost typically £100 to £250 per scan. NHS DXA is generally restricted to osteoporosis investigation rather than routine body composition; the DEXA Trust and similar private operators provide more accessible booking.

Why DXA matters on GLP-1

Total weight loss says nothing about composition. A patient who loses 15 kg can lose 12 kg fat and 3 kg lean, or 9 kg fat and 6 kg lean. The functional outcome is wildly different. Baseline DXA plus follow-up at 6 and 12 months tracks composition rather than weight alone. Longevity clinics integrating DXA into GLP-1 programmes can adjust protein and training prescriptions if the lean-mass loss is excessive.

Related: sarcopenia · VAT · longevity hub.