Your DEXA scan, explained: what the numbers actually mean
A DEXA scan can tell you what the scale can't: whether a stalled week is really a stall. Here is how to read the report, line by line.
- DEXA splits your weight into fat, lean tissue and bone, region by region.
- Fat percentage tells you more than scale weight during a plateau.
- Visceral fat, the fat around your organs, often improves before the scale moves.
- Scan every 8 to 12 weeks under the same conditions, and treat changes under 1 to 2 percent as noise.
- If lean mass is dropping with fat, fix protein and strength training before cutting calories.
Week three. You have been careful, you have logged everything, and the scale has not moved. Is the plan failing, or is something else going on?
Your scale can't answer that, because it only knows your total weight. A DEXA scan can. It separates fat from muscle, water and bone, so you can see whether you are still losing fat while something else hides it.
What a DEXA scan is
DEXA (dual-energy X-ray absorptiometry) was first used to measure bone density, and it is now one of the most trusted ways to measure body composition.1 It passes two low-dose X-ray beams through your body. Fat, lean tissue and bone absorb them differently, so the machine can work out how much of each you carry, for your whole body and for each region: arms, legs and trunk.
The scan itself is easy. You lie still on an open table for about 10 minutes while an arm passes over you. No tube, no needles. The radiation dose is very small, a fraction of a standard chest X-ray. You walk out with a colour image and a report.
Reading your report, line by line
The report can look like a wall of numbers. These are the ones that matter.
Body fat percentage vs fat mass. Percentage is a ratio; fat mass is the actual amount. At 200 lbs (91 kg) and 35 percent body fat, you carry 70 lbs (32 kg) of fat. Lose 10 lbs of fat while gaining 4 lbs of muscle and the scale barely moves, but your percentage drops. That is why percentage is the better plateau detector.
Lean mass, or fat-free mass. This is everything that isn't fat: muscle, bone, water and organs. If it holds steady while fat drops, your stuck week wasn't stuck. If it falls quickly along with fat, often after very aggressive dieting, that is a warning sign worth acting on.
Visceral fat (VAT). This is the fat stored around your organs, and it is the type most linked to health risk. It often responds to a calorie deficit sooner than the fat under your skin, so it can be the first number to improve while your weight looks flat.
The regional breakdown.
| Line on the report | What it shows | Why it matters |
|---|---|---|
| Trunk fat | Fat around the belly and torso | Often the slowest to change, and closely tied to visceral fat |
| Android / gynoid ratio | Belly fat compared with hip and thigh fat | Shows where your body tends to store fat |
| Arm and leg lean mass | Muscle in each limb | Catches muscle loss, or one side lagging |
Fat doesn't come off evenly. If your legs lean out before your belly, that is normal, not a sign that something is wrong.
How accurate is DEXA compared with other methods?
DEXA is about as close to a gold standard as most people can easily get, typically within 1 to 2 percent body fat. Other methods vary more:
- Smart scales send a weak current through your feet and estimate fat from how much water they detect. Hydration, a salty dinner or a workout can swing the reading by several points from one morning to the next.
- Skinfold calipers can be decent in skilled hands, but the result depends heavily on who is pinching and where.
- Underwater weighing and air displacement pods are solid, but they need a lab visit, often cost about the same as DEXA, and don't give you bone or regional data.
For day-to-day tracking, a consistent method beats a precise one. Use your scale or tape measure for the weekly trend, and treat DEXA as the checkpoint that tells you whether the trend is real.
If you want a number between scans, Leanova includes a tape-measure body fat estimate based on the US Navy method, with its research sources shown in the app. It isn't a DEXA and doesn't pretend to be, but measured the same way each time, it shows you the direction you're heading.
What is a healthy body fat percentage?
There isn't one perfect number. Healthy is a range, and the range shifts with age and sex. The American Council on Exercise puts average body fat at roughly 25 to 31 percent for women and 18 to 24 percent for men, with lower ranges for fit and athletic people. Women naturally carry more essential fat than men, so a reading that looks high on a men's chart is often perfectly normal for a woman.
If you have 20 to 50 lbs (9 to 23 kg) to lose, your exact number matters less than the direction it moves between scans.
How to prepare so your scans can be compared
Preparation matters less for one scan than for comparing two. If the conditions change, the difference between scans can look like progress that isn't there, or hide progress that is.
- Book the same time of day for every scan.
- Skip food for a few hours beforehand, as your provider advises.
- Skip your workout that day. Exercise shifts water into your muscles and can inflate lean mass.
- Drink normally, but not a large amount right before.
- Wear clothes with no metal: no zips, underwires or jewellery.
- Tell the technician about any implants or recent scans that used contrast.
How often to scan, and what counts as real progress
For a weight-loss phase, every 8 to 12 weeks is plenty. Body composition changes slowly, and scanning more often mostly measures water. A simple rhythm: a baseline before you start, a second scan around week 10 to 12, then every three months or so.
Treat changes smaller than about 1 to 2 percent body fat, or 1 to 2 lbs of fat mass, as within the margin of error. Real progress looks like fat mass going down while lean mass holds roughly steady.
If lean mass is dropping alongside fat, raise your protein and add or increase strength training before you cut calories any further. And if the scale stalled but your belly fat fell, your plateau was never really a plateau.
Is a DEXA scan worth it for you?
It is worth paying for when you have stalled for a few weeks and need to know whether you are still losing fat. That answer decides whether you keep going as you are or change something.
Early in a diet, cheaper tools are usually enough: a weekly waist measurement, your weight trend and the occasional progress photo. DEXA is not recommended during pregnancy, and metal implants such as a hip replacement can affect the regional readings. If you have a medical condition, talk to your doctor or a dietitian about what your results mean for you.
Common questions
How much does a DEXA scan cost?
In the US, a body composition scan typically costs somewhere between $40 and $150 out of pocket, depending on where you go. Some clinics offer discounted packages for repeat scans.
Is a DEXA scan safe?
Yes. The radiation dose for a body composition scan is very low, a small fraction of a standard chest X-ray. Spacing scans 8 to 12 weeks apart is not a meaningful concern for most people. It is not recommended during pregnancy.
Will insurance cover a DEXA scan for body fat?
Usually not. Insurance tends to cover DEXA for bone density when it is medically needed, but body composition scans are normally paid out of pocket. Call the clinic and your plan before you book.
Why is my DEXA body fat higher than my smart scale says?
Smart scales estimate fat from body water and mostly read the current through your legs, so hydration and where you store fat can throw them off. DEXA measures tissue directly. Use your scale for the trend and DEXA for the true number.
Does a DEXA scan hurt?
No. You lie still on an open table for about 10 minutes. There are no needles and nothing touches you.
Sources
- Shepherd JA, Ng BK, Sommer MJ, Heymsfield SB. Body composition by DXA. Bone, 2017. https://doi.org/10.1016/j.bone.2017.06.010