What a DEXA Scan Actually Measures

Most people step on a scale and get one number. That number is the sum of everything you carry: fat, muscle, bone, water, and whatever you ate for lunch. It cannot tell you which of those changed. A DEXA scan breaks that single number into its parts.

How it works

DEXA stands for dual energy X ray absorptiometry. The scanner passes two low energy X ray beams over your body while you lie still on a table for about 10 minutes. Fat, lean tissue and bone absorb those two energies differently, so the machine can sort each small area of your body into one of the three. The radiation dose is very low, a small fraction of a standard chest X ray.

What the report shows

A DEXA report gives you much more than a body fat percentage. The main pieces are:

• Fat mass, in pounds, and your total body fat percentage.
• Lean mass, which is mostly muscle, along with organs and water.
• Bone density, a key measure of how strong your skeleton is.
• Regional numbers for each arm, each leg and the trunk.
• An estimate of visceral fat, the fat packed around your organs.

The regional breakdown is where much of the value lives. Two people with the same body fat percentage can carry it very differently. One stores more in the hips and thighs. The other stores more in the trunk, and more of that sits around the liver and intestines. The second pattern carries more metabolic risk, and a scale would never show the difference.

Lean mass in the arms and legs is also what we use to calculate ALMI, a muscle index we compare to people of your age and sex. Low arm and leg muscle predicts frailty and falls later in life, so it is worth knowing where you stand well before that becomes a problem.

Why we use it

DEXA is the gold standard for body composition because it measures tissue more directly than other methods, which estimate it from indirect signals. It is not thrown off much by how much water you drank that morning. That makes it reliable for comparing one scan to the next.

We repeat DEXA about every 6 months. That is long enough for real changes in muscle, fat and bone to show up, and short enough to catch a plan that is not working. A hypothetical 50 year old man who loses 15 pounds could find that 12 came from fat and 3 from lean mass, or the reverse. Those are two very different results, and only a scan tells you which one you got.

That's the kind of thing we measure. The scan costs $199, and you can pick your time right after you buy.

Book a DEXA scan at HYBRD Health ($199)

This article is educational and is not medical advice.