DEXA measures body composition directly; bioimpedance estimates it. In a 2026 study of 1,250 adults, a standing 8-point BIA device tracked closely with DEXA for fat mass but read body fat percentage 3 to 4 points lower on average. That makes BIA a strong trend tool and DEXA the reference.
How each method works
DEXA (dual-energy X-ray absorptiometry)
DEXA passes two low-dose X-ray beams through the body. Because bone, fat and lean tissue absorb them differently, the scan separates the three directly and maps them by region (arms, legs, trunk, visceral area). Results are highly repeatable, which is why DEXA is the reference method in research and the standard for bone density.
Bioimpedance (BIA)
BIA measures resistance to a small electrical current and estimates body water, then lean mass and fat mass, using prediction equations. Multi-frequency, 8-electrode devices read each limb and the trunk separately and are more detailed than single-frequency foot scales.
What the research shows
A 2026 study compared a standing 8-point multi-frequency BIA device with same-day DEXA scans in 1,250 adults aged 18 to 80:
- Fat mass agreed closely with DEXA (concordance 0.91 in men and 0.95 in women).
- Body fat percentage read lower on BIA by about 3.6 points in men and 4.3 points in women.
- Lean mass read higher on BIA by about 3.1 to 3.3 kg.
The authors concluded that BIA is well suited to repeated measurements on the same device, and that DEXA should be used for precise individual assessment and clinical decisions. That is exactly the split we recommend.
Side-by-side comparison
| DEXA | Bioimpedance | |
|---|---|---|
| Method | Direct measurement with low-dose X-ray | Estimate from electrical resistance |
| Bone density | Yes | No |
| Regional fat and lean mass | Yes, detailed | Segmental on 8-electrode devices |
| Visceral fat | Measured | Estimated |
| Sensitive to hydration | Low | High |
| Typical use | Baseline and every 8–12 weeks | Weekly trend tracking |
| Cost per reading | Per scan at a clinic | Near zero after purchase |
When to use each
- Use DEXA for your starting point, for checkpoints every 8–12 weeks, for bone density, and whenever a clinical decision depends on the number.
- Use BIA between scans to see the direction of change and to stay engaged with your plan.
- Never mix devices. Compare BIA readings only with earlier readings from the same device.
Pair a DEXA baseline with consistent at-home tracking.
Find a DEXA scan near youDEXA+ Body Fat ScaleFrequently asked questions
Is bioimpedance accurate?
Good BIA devices correlate strongly with DEXA, especially for fat mass, but individual readings can differ by several percentage points. They are most useful for tracking change on the same device.
Why is my BIA body fat lower than my DEXA body fat?
Many BIA devices underestimate body fat compared with DEXA. In one large study the average gap was about 3.6 points in men and 4.3 points in women.
Can I compare readings from two different BIA devices?
No. Each device uses its own equations. Compare readings only on the same device, under the same conditions.