DEXA body composition scans: how they compare and what the numbers mean
Written by a UK GP · Updated
A DEXA body composition scan measures how much of your body is fat, lean tissue (mostly muscle, organs and water) and bone — and where it is. Instead of a single body-fat percentage, you get a breakdown for your arms, legs and trunk, and usually an estimate of visceral fat.
DEXA vs smart scales, InBody and callipers
| Method | How it works | Main limitations |
|---|---|---|
| DEXA | Two low-dose X-ray beams distinguish fat, lean tissue and bone, region by region | Costs more; small X-ray dose; results vary slightly between machines |
| Bioimpedance (smart scales, InBody) | A small electrical current estimates body water, then fat and lean mass by equation | Sensitive to hydration, food, exercise and time of day |
| Skinfold callipers | Pinches of skin at set sites are measured and fed into an equation | Only measures fat under the skin; depends heavily on who takes the measurement |
DEXA is widely used as a reference method in research because it measures each region directly rather than estimating from a single reading. It isn't perfect — hydration still affects the lean mass figure, and different scanners can give slightly different numbers — so it's best for tracking change on the same machine.
What your report shows
- Total and regional body fat in kilograms and as a percentage
- Lean mass by region, useful for seeing whether training or weight loss is preserving muscle
- Visceral fat estimate (see below)
- Bone mineral content for the whole body (this is not the same as a diagnostic bone density scan of the hip and spine)
What is visceral fat?
Visceral fat sits inside the abdomen, around organs such as the liver and intestines, rather than under the skin. Higher levels are associated with a greater risk of type 2 diabetes and heart disease, even in people whose weight is in the “healthy” range. DEXA software estimates it from the area around your waist. Scales and tape measures can only approximate it.
A visceral fat figure is a number to discuss, not a diagnosis. If yours is flagged as high, your GP can look at it alongside things like blood pressure, cholesterol and blood sugar.
How often should you scan?
Body composition changes slowly, and every measurement has a small margin of error. Many people rescan every three to six months when they are tracking a training or weight-loss programme; scanning more often is unlikely to show a change bigger than that margin. Each scan is a small X-ray dose, which is why clinics ask screening questions before booking.
For the most comparable results each time:
- use the same clinic and scanner
- scan at the same time of day, ideally after an overnight fast
- avoid hard exercise and large amounts of fluid beforehand
- wear similar, metal-free clothing
Who shouldn't have one
DEXA isn't suitable during pregnancy. Scanners also have a weight limit and a maximum width, so check with the clinic if that might apply to you.
Frequently asked questions
Is a DEXA body composition scan accurate?
It is one of the more precise ways to measure body composition outside a research lab, and it measures each body region separately. Hydration and the specific scanner still affect results, so compare scans from the same machine.
How much does a body composition DEXA scan cost?
Prices vary by clinic, what's included and whether you buy a package. Our UK price guide shows current checked prices by city.
Can I get a body composition scan on the NHS?
Not usually. DEXA body composition scans for fitness or general health tracking are almost always private.
Find a body composition scan by city
This page is general information, not medical advice, and doesn't replace a consultation. If you're worried about your bone health or weight, speak to your GP.