What Is a DEXA Scan and How Does It Measure Body Composition?

Two people can weigh exactly the same and have completely different bodies. That is the gap a DEXA scan fills. It is often called the gold standard for body composition, and it takes about seven minutes. Here is what a DEXA scan is, how it works, what it measures and what to expect at Prefusion Health in New York.

What is a DEXA scan?

DEXA stands for Dual-Energy X-ray Absorptiometry. It is a medical-grade scan that measures body fat percentage, lean muscle mass, visceral fat and bone mineral density in one non-invasive session of about seven minutes.

It gives you a true picture of your body: not an estimate from a scale or a watch, but a measurement. Prefusion Health uses a medical-grade GE DEXA scanner, and your results are explained by your care team before you leave.

How does a DEXA scan work?

The idea is simple. Fat, lean muscle and bone absorb X-rays differently. A DEXA scanner passes low-dose X-rays at two energy levels through your body, and by comparing how much is absorbed, it separates your body into its components. That is the "dual-energy" part of the name.

The result is a detailed breakdown of what your weight is actually made of, and where it sits. The radiation dose is very low, which is why the scan is suitable for regular retesting.

What a DEXA scan measures

A standard DEXA scan at Prefusion Health gives you:

• Total body fat percentage and where it is distributed
• Lean muscle mass by region, including left versus right and arms versus legs
• Visceral fat, the deep fat stored around your organs
• Bone density

Visceral fat: the number most people have never seen

Visceral fat sits around your internal organs rather than under your skin, and it is the fat most closely linked to long-term metabolic risk. A DEXA scan is one of the few accessible tests that can measure it. A scale, a wrist device or calipers cannot.

Regional muscle and imbalances

Because the scan reports lean mass by region, it shows left-right and regional muscle imbalances. Your training plan can then address them directly instead of guessing.

Bone density

The same scan reads bone density, an early health marker that most routine checkups skip.

Why DEXA beats the scale

A scale measures one thing: total weight. It cannot separate fat from muscle, and it cannot see visceral fat. Body fat scales estimate fat using a small electrical signal, which shifts with how hydrated you are. DEXA measures fat, muscle and bone directly.

That difference matters most when you are working toward a goal. If you are losing weight, you want to know whether it is fat or muscle. If you are training hard, you want to know whether you are actually building muscle. The scale cannot tell you. DEXA can.

How often should you get scanned?

If you are actively working toward a fitness or weight-loss goal, scanning about every 90 days gives your body enough time for a meaningful, measurable change between scans. One Prefusion member, Nicole, scanned in January and came back in May: she had lost 4.5% body fat, and the scan showed exactly where it came from.

If you plan to retest, the Metabolic Reset (two DEXA scans and an RMR test) and the Flex Pack (four tests in any mix of DEXA and RMR) are built for it.

What to expect at your visit

1. Book online. Choose Manhattan, Bellmore or Stony Brook and pick a time.
2. Your scan, about seven minutes. You lie still on the scanner, fully clothed in metal-free clothing. No needles, no discomfort.
3. Walk through your numbers. Your care team reviews the report with you and explains what it means and what to do next.

Where a DEXA scan fits

A DEXA scan shows what your body is made of. It does not show why. If you want the full picture, the Prefusion Protocol combines DEXA with an RMR test and comprehensive labs, reviewed by our medical team. If you want your full physical baseline in one visit, the Optimization Pack adds RMR and VO2 max.