What Is a DEXA Scan? A Naples Physician Explains Body Composition and Bone Density

If you have been told to "get a body composition test," you have probably run into a wall of choices. Bathroom scales, handheld gadgets, the InBody machine at the gym, and something called a DEXA scan. They do not all measure the same thing, and they do not all give you the same answer.

Here is what a DEXA scan is, what it can tell you, and why we use it at Naples Longevity Clinic.

What a DEXA scan actually is

DEXA stands for dual energy X-ray absorptiometry. The scanner passes two very low energy X-ray beams through your body. Bone, muscle, and fat each block those beams by a different amount, and the machine reads the difference to work out how much of each you have, and where it sits.

You lie on an open table, fully clothed, and nothing touches or encloses you. A whole body scan takes about ten minutes.

The technology is not new. It has been the reference method for bone density in hospitals for decades. What is new is how often you see it outside of radiology, in longevity and performance clinics like ours, because the same scan that reads your bones also produces the most reliable body composition numbers available in an outpatient setting.

A DEXA scan reports four things:

1. Fat mass, in pounds and as a percentage, region by region

2. Lean mass, which is mostly muscle, measured separately for each arm, each leg, and your trunk

3. Visceral fat, the deep abdominal fat around your organs, reported as an actual weight rather than a guess

4. Bone density, at the hip, spine, and forearm, reported as a T score

That regional detail matters more than people expect. Two people can weigh the same, carry the same total body fat, and have completely different risk profiles because of where that fat sits and how much muscle is holding up each leg.

DEXA vs. InBody: why the numbers do not match

InBody and similar scales use bioelectrical impedance. They send a small current through your body and estimate your composition from how easily it travels. Water conducts well, fat does not, so the math works backwards from resistance.

That approach has real advantages. It takes thirty seconds, it costs almost nothing per test, and it is excellent for tracking week to week. We are not against it.

But it estimates, and the estimate leans in a predictable direction. When researchers compared InBody devices head to head against DEXA, the impedance devices consistently read body fat too low and lean mass too high, with an average gap of roughly 3 to 4 percentage points of body fat.

Impedance also cannot see your bones at all, and its reading shifts with how hydrated you are, when you last ate, and when you last trained.

So the honest way to put it is this. Impedance is a good habit. DEXA is the better number, and it is the one everything else gets compared against.

What we actually use DEXA for

Bone density

This is the original use, and still the most important one. A T score tells us whether your bone density is normal, low, or in the osteoporosis range, and it can catch a problem years before a fracture does.

Current national guidance recommends bone density screening for women 65 and older, and for younger postmenopausal women whose fracture risk is already elevated. For men, the U.S. Preventive Services Task Force says the evidence is not strong enough to make a recommendation at all 

Those guidelines exist to allocate population screening, and they do that job reasonably well. But they are a floor, not a ceiling. If you are 52, you lift nothing heavier than a grocery bag, your vitamin D has been low for years, and you just dropped 40 pounds, waiting until 65 to look at your bones is a strange plan.

Body composition

The second use is measuring what your weight is actually made of.

The number I care most about is visceral fat. That is the metabolically active fat packed between your organs and around your liver, and it behaves differently from the fat under your skin. It releases free fatty acids and inflammatory signals straight into the portal circulation, and it tracks with insulin resistance, type 2 diabetes, fatty liver, high blood pressure, and cardiovascular disease independently of your total body fat . One analysis found that a one standard deviation increase in visceral fat raised the odds of insulin resistance by 80 percent, while the same increase in fat under the skin lowered them.

The muscle numbers matter just as much. Knowing you carry 6.1 pounds of lean mass in your right arm and 5.4 in your left, or that your legs are underbuilt for your frame, turns "you should exercise" into an actual prescription. And when we scan you again in six months, we can tell whether the plan built muscle or just cost you weight.

A word about GLP-1 medications

Semaglutide and tirzepatide are genuinely useful drugs. I prescribe them. But the pounds that come off are not all fat.

A meta-analysis of seven randomized trials found that about 30 percent of the total weight lost on GLP-1 therapy came from lean mass, roughly 1.9 kg on average. Bone takes a hit too. In a 52 week randomized trial, semaglutide reduced bone density by about 2.6 percent at the hip and 2.1 percent at the spine compared with placebo, with markers showing increased bone breakdown and no matching increase in bone building .

None of that is a reason to avoid these medications. It is a reason to measure. If you are on a GLP-1, a scan before you start and another six to twelve months in tells you whether you are losing the right tissue, and it gives us time to fix the protein and the resistance training if you are not.

What about the radiation?

DEXA uses X-rays, so it uses radiation. The dose is tiny.

A whole body DEXA delivers on the order of 0.001 to 0.01 mSv. A single chest X-ray is about 0.1 mSv, and the average American absorbs roughly 3 mSv a year just from the natural background. In practical terms, one scan sits somewhere around a few hours of ordinary living. That is low enough that repeating it every six months to track progress is not a concern.

We do not scan anyone who is pregnant or might be, and recent barium studies or nuclear medicine tests need to clear your system first.

Bone loss is showing up earlier than the guidelines assume

The picture we were taught, osteoporosis as a disease of women after 65, does not match what walks into the clinic.

We are seeing low bone density in people in their forties and fifties. The pattern is fairly consistent: rapid weight loss, no resistance training, protein intake well under what they need, and vitamin D that has been low for years without anyone acting on it. Several of those things are fixable, and all of them are invisible until somebody measures.

You do not get bone back easily. Loading it, eating enough protein, correcting vitamin D, and keeping your hormones in a sensible range all work far better as prevention than as repair. That argument only lands if you know your starting number.

So ask your physician about a bone density scan. Ask what your T score is, when it was last checked, and what your plan is for keeping it where it should be.

Getting a DEXA scan in Naples and Bonita Springs

We run DEXA at Naples Longevity Clinic for body composition, bone density, or both, and every scan is read and explained by a physician. You do not get a printout and a handshake. You get a sit down where we go through what the numbers mean for you, and what changes in your training, nutrition, and labs follow from them.

Many patients pair the scan with VO2 max testing, which measures how well your heart, lungs, and muscles use oxygen. Together they cover the two things that predict how well you age: how much muscle you carry, and how well your engine runs.

To book a scan or ask a question, visit napleslongevity.com and click Request Appointment, or call us at 239-659-3266.

Tareq Khader, MD is board certified in internal medicine and the founder and medical director of Naples Longevity Clinic, serving Naples, Bonita Springs, Fort Myers, and Cape Coral, Florida.

This article is for general education and is not medical advice. It does not replace a consultation with your own physician.

Last reviewed: August 2026