Your DEXA scan, decoded.
Your scale gives you one number. A DEXA scan gives you the numbers that actually matter. Here's how to read them.
The short version
- DEXA splits your body into fat, lean mass, and bone, and shows where each one sits.
- The three numbers to watch: visceral fat, lean mass (especially in your arms and legs), and bone density.
- Body fat % is useful, but the trend matters more than the number.
- Retest every 3–6 months, under the same conditions every time.
What a DEXA scan actually measures
DEXA (dual-energy X-ray absorptiometry) uses two very low-dose X-ray beams to separate your body into three things: fat mass, lean mass, and bone mineral. It takes about 7–10 minutes lying on a table, and the radiation dose is a small fraction of a standard chest X-ray.
Unlike a bathroom scale or a smart scale, DEXA doesn't estimate from a formula. It measures each region of your body: arms, legs, trunk, and the fat around your organs.
The numbers on your report
| Number | What it is | Why it matters |
|---|---|---|
| Body fat % | Fat mass ÷ total mass | The headline number. Good for tracking trends, not for comparing with friends. |
| Lean mass | Everything that isn't fat or bone: muscle, organs, water | Your engine. Losing it slows your metabolism and weakens your joints. |
| Visceral fat (VAT) | Fat stored around your organs, deep in your abdomen | The fat most linked to metabolic and heart disease risk. |
| ALMI | Lean mass in your arms and legs, adjusted for height | The best DEXA marker for muscle. Low values signal age-related muscle loss. |
| Bone density (T-score / Z-score) | How dense your bones are vs. a healthy young adult (T) or your age group (Z) | Early warning for osteopenia and osteoporosis. |
| Regional breakdown | Fat and lean mass in each arm, leg, and your trunk | Shows left-right imbalances, often left over from old injuries. |
1. Visceral fat: the number to watch first
Subcutaneous fat sits under your skin. Visceral fat sits around your liver, intestines, and other organs, and it's metabolically active in the worst way. Higher visceral fat is associated with insulin resistance, high blood pressure, and cardiovascular disease, even in people who don't look overweight.
What to do with it: lower is better, and the trend is what matters. Visceral fat tends to respond quickly to a calorie deficit, strength training, better sleep, and less alcohol. It's often the first number to move.
2. Lean mass and ALMI: is your muscle holding up?
Total lean mass includes water and organs, so it can swing a pound or two depending on hydration. ALMI (appendicular lean mass index) is a cleaner muscle signal: it's the lean mass in your arms and legs divided by your height squared.
Researchers use ALMI to flag low muscle mass. One widely used European consensus (EWGSOP2) puts the cutoff at about 7.0 kg/m² for men and 5.5 kg/m² for women. Most active adults will be well above that. The goal is to stay well above it as you age, and to make sure it doesn't drop while you lose fat.
The best result on a fat-loss DEXA: body fat down, visceral fat down, and lean mass and ALMI flat or up.
3. Body fat %: useful, but don't obsess
Healthy ranges depend on sex and age, and different scanners give slightly different numbers. As a rough guide, many active men land somewhere in the mid-teens to low 20s, and many active women in the low 20s to around 30%. Lower isn't automatically better. Very low body fat comes with real costs to hormones, energy, and recovery.
Use body fat % as a direction-of-travel number. A 2–3 point drop over a few months with lean mass holding steady is excellent progress.
4. Bone density: the long game
Your T-score compares your bones to a healthy young adult. The standard categories are:
- −1.0 or higher: normal
- Between −1.0 and −2.5: low bone mass (osteopenia)
- −2.5 or lower: osteoporosis range
Body composition DEXA scans give a useful screen, but a formal diagnosis uses a dedicated hip and spine scan ordered by your doctor. If your numbers are low, talk to your physician. Heavy, progressive strength training and impact work are some of the best tools for building and keeping bone.
5. Left vs. right: the hidden imbalance
The regional breakdown shows lean mass in each arm and leg. A difference of more than a few percent between sides often shows up after an old ankle, knee, or shoulder injury where one side quietly stopped doing its share. It's exactly the kind of thing a movement assessment catches, and that targeted training fixes.
How to get accurate, comparable scans
Small changes in hydration, food, and timing can shift your lean mass reading by a pound or more. Keep conditions the same every time:
- Scan at the same time of day, ideally in the morning
- Same eating and drinking routine beforehand (many people scan fasted)
- No hard workout in the hours before
- Same clothing, no metal
- Same scanner brand or location if possible
How often: every 3–6 months is the sweet spot. Real changes in fat and muscle take time, and scanning more often mostly measures noise.
Common questions
Is DEXA more accurate than a smart scale?
Yes. Smart scales estimate body fat by running a small electrical current through your body, and they're heavily affected by hydration. DEXA measures directly and gives you regional detail.
Why did my lean mass drop even though I've been lifting?
Some of it is often water and glycogen, especially during a calorie deficit or a low-carb phase. Look at the trend across two or three scans, and check whether your strength is holding. If both are dropping, protein, training, or recovery need attention.
What's a good visceral fat number?
Different scanners report it differently (pounds, grams, or area). Compare against your own previous scans and the reference ranges on your report, and aim to bring it down over time.
Turn your scan into a plan.
Every MB Online coaching plan includes a baseline DEXA and a 6-month retest at any BodySpec location you choose, plus nutrition targets set from your lean mass and a program built from your movement assessment.
This guide is educational and is not medical advice. It does not diagnose, treat, or replace care from your physician. Talk to your doctor before starting a new exercise program, especially if you have a medical condition. Bone density concerns should be evaluated by a physician with a dedicated diagnostic scan.