Guide · Updated November 2026

My DEXA Scan Results After 6 Months on Mounjaro: How Much Muscle Did I Actually Lose?

After 6 months on Mounjaro (10mg), I lost 41 lbs total: 35.3 lbs of fat and 5.5 lbs of lean mass, so about 13.4% of my weight loss was lean mass, compared with about 25% in the SURMOUNT-1 DEXA substudy. My body fat dropped from 39.8% to 30.6% and visceral fat area fell from 187 cm² to 94 cm². I think resistance training and high protein intake helped, though one person's scans cannot prove that.

Six months in, 41 pounds down, and a nagging question I couldn’t answer from the scale alone: how much of that was actually fat?

The number that kept me up at night wasn’t my weight. It was the idea that I might be shrinking the wrong tissue. Losing muscle is quiet. You don’t feel it happening. Your clothes still fit better. The scale still moves. But metabolically, losing lean mass is the opposite of what you want, and it can set you up for weight regain once you slow down or stop.

So I got a DEXA scan before I started Mounjaro and another one at the six-month mark. Here’s exactly what the numbers showed, how they compare to what the clinical trials predicted, and what I changed between scans based on what I learned. For a broader look at why the fat-versus-muscle distinction matters on GLP-1s, see my guide on fat loss vs. weight loss on GLP-1s.

My Baseline: What the First DEXA Showed

I got my first scan in late August 2025 at a sports medicine clinic, about two weeks before my first Mounjaro injection. The technician walked me through the printout, which is honestly overwhelming the first time you see it.

The key numbers from that baseline scan:

• Total weight: 247 lbs
• Total fat mass: 98.4 lbs (39.8% body fat)
• Lean mass: 140.6 lbs
• Bone mineral content: 8.0 lbs
• Visceral fat area: 187 cm²

That visceral fat number was the one my doctor kept pointing to. Visceral fat is the fat packed around your organs. Some studies and guidelines, mostly from Japan and based on CT scans, use 100 cm² as a cutoff for higher metabolic risk. DEXA estimates of visceral fat are not identical to CT measurements, so treat that cutoff as a rough guide.

I started at 2.5mg and titrated up to 10mg over about four months. The Mounjaro label starts at 2.5 mg and raises the dose in 2.5 mg steps after at least 4 weeks on each dose. Your prescriber sets the pace. The nausea on the 7.5mg dose was real, and I stayed there an extra month before going up. By month six I was sitting at 10mg with no plans to go higher, at least for now.

The Six-Month Scan: My DEXA Results on Mounjaro

I went back to the same clinic, same machine, same time of day. That consistency matters. DEXA results can shift with hydration and meal timing, so repeating the conditions as closely as possible gives you cleaner data. You can also estimate your body composition between scans with our body composition calculator.

Six months later:

• Total weight: 206 lbs (down 41 lbs)
• Total fat mass: 63.1 lbs (down 35.3 lbs, 30.6% body fat)
• Lean mass: 135.1 lbs (down 5.5 lbs)
• Bone mineral content: 7.8 lbs (down 0.2 lbs)
• Visceral fat area: 94 cm² (down 93 cm²)

That visceral fat drop was the number that genuinely surprised me. Nearly cut in half. That alone felt worth the whole process.

The lean mass number is where I had complicated feelings. I lost 5.5 lbs of lean mass out of 41 lbs total, which works out to about 13.4% of my total weight loss coming from lean tissue. The other 86.6% was fat.

Honestly? That’s better than I expected based on what I’d read, but it’s not zero, and I want to be clear about that.

How My Results Compare to the Clinical Trials

The SURMOUNT-1 trial is the big one for tirzepatide. In that study (NEJM, 2022, n=2,539), participants on the 15mg dose lost an average of 20.9% of their body weight at 72 weeks. A DEXA substudy of 160 participants (Look et al., Diabetes, Obesity and Metabolism, 2025) pooled all tirzepatide doses and found that about 25% of the weight lost was lean mass.

STEP 1, the equivalent trial for semaglutide 2.4 mg (NEJM, 2021), had a smaller DEXA substudy of 140 people. Fat mass fell 19.3% and lean mass fell 9.7% on semaglutide, which works out to lean mass making up roughly 40% of the tissue lost. The two substudies used different methods, so the comparison is rough.

My 13.4% sits below both of those figures. A few possible reasons:

1. I was actively resistance training three times per week throughout the six months.
2. I increased my protein intake to around 160-180 grams per day starting in month two.
3. I was on 10mg, not 15mg.
4. Individual variation is real, and a single scan pair has measurement error.

I want to be careful not to oversell this. My single data point doesn’t tell you what will happen to you. But it does suggest that the trial averages aren’t a ceiling, and that the things you do while on the medication genuinely seem to matter.

Sources: SURMOUNT-1 (NEJM), SURMOUNT-1 DEXA substudy (Look et al. 2025), STEP 1 (NEJM), STEP 1 DEXA substudy, linked above.

The Visceral Fat Story

The 93 cm² drop in visceral fat is the number I keep coming back to. Going from 187 cm² to 94 cm² moved me from the high-risk category to right at the borderline, in six months.

This matters because visceral fat doesn’t just sit there. It secretes inflammatory cytokines and is directly linked to insulin resistance, type 2 diabetes, and cardiovascular disease. In the STEP 1 DEXA substudy, visceral fat fell 27.4% compared with 19.3% for total fat, and my scan showed a similar pattern.

The visceral fat number also reframes the lean mass question a bit. Some of what DEXA categorizes as “lean mass” loss on GLP-1s may actually be water and glycogen stored in fat-adjacent tissue, not contractile muscle fiber. The scan can’t perfectly distinguish. The SURMOUNT-1 substudy authors note that DEXA lean mass includes muscle, organs, and water, so it is not a pure muscle measurement.

That doesn’t mean muscle loss isn’t happening. It is. But the picture is more complex than “you lost X pounds of muscle.”

What I Did to Protect Muscle

I’m not going to pretend I had a perfect protocol. But here’s what I actually did consistently:

Protein intake. I tracked this obsessively for the first three months and more loosely after that. My target was 0.8-1.0 grams per pound of body weight. At 247 lbs starting weight, that’s a lot of protein, and the appetite suppression from Mounjaro made hitting that target harder in some weeks. My average ended up around 155 grams per day, not the 200 I was theoretically aiming for.

Resistance training. Three sessions per week, focused on compound lifts. I didn’t add volume or intensity, I just maintained what I was already doing before starting Mounjaro. I did not start a new program mid-weight-loss. That felt like too many variables.

Creatine. 5 grams per day, every day. Creatine has good evidence for lean mass gains with resistance training, though the evidence during calorie restriction is thinner. See my creatine guide.

Eating on injection day. The 24 hours after injection were often my lowest appetite days. I made a rule that I had to hit at least 120 grams of protein on injection day even when I didn’t want to eat. This was the hardest part.

For more on the exercise and protein side of things, the exercise and muscle guide on ClearMetabolic goes deeper into the research on GLP-1 and resistance training.

What a DEXA Scan Actually Measures (and What It Misses)

If you’ve never had a DEXA scan, here’s the short version. DEXA stands for Dual-Energy X-ray Absorptiometry. It uses two different X-ray energy levels to differentiate between bone, fat, and lean soft tissue across your whole body. The scan takes a few minutes and the radiation dose is very low.

What it measures well: total fat mass, regional fat distribution, bone mineral density, and a reasonable estimate of lean mass.

What it doesn’t measure: muscle quality, muscle fiber type, or intramuscular fat. It also can’t distinguish between skeletal muscle and organ mass under the “lean” category. Your liver counts as lean mass.

For tracking changes over time, it is one of the most practical options outside a research lab. MRI gives more precise muscle data but costs more and is not practical for routine tracking. Bioelectrical impedance (like the InBody machines at gyms) is convenient but is more affected by hydration shifts.

My scans cost $95 each at a sports medicine clinic. Prices vary a lot by area. If you’re trying to keep overall costs down while on a GLP-1, our cheapest GLP-1 options guide can help free up budget for tracking tools like DEXA. The key is using the same machine and protocol each time, not jumping between providers.

Regional Body Composition: Where Did the Fat Actually Come From?

One thing I wasn’t prepared for was the regional breakdown the scan provides. The printout shows fat and lean mass separately for your trunk, arms, and legs.

My regional changes over six months:

The trunk (midsection and chest) accounted for the largest share of fat loss, which tracks with what’s known about visceral and abdominal fat responding strongly to GLP-1 therapy.

The leg lean mass loss of 2.6 lbs is the number I watch most carefully going forward. Leg muscle is critical for metabolic rate, mobility as you age, and glucose disposal. I’ve added more lower body volume to my training since the six-month scan.

My Honest Take on the Muscle Loss Question

Here’s where I land after six months of data: yes, you lose some muscle on Mounjaro. The clinical trials show it, my scan shows it, and anyone who tells you GLP-1s are perfectly muscle-sparing is either misinformed or selling something.

But 5.5 lbs of lean mass lost while losing 41 lbs total, and nearly halving visceral fat, with body fat percentage dropping from 39.8% to 30.6%? I’ll take that outcome.

The more useful question isn’t “did I lose muscle?” It’s “how much muscle did I lose relative to fat, and does that ratio make me metabolically better or worse off than before?” By that framing, I’m clearly better off. My lean-to-fat ratio improved significantly, and the metabolic risk associated with that visceral fat number dropping below 100 cm² is real and meaningful.

The SURMOUNT-1 DEXA substudy points the same way at the population level. Fat mass decreased 33.9% while lean mass decreased 10.9% on tirzepatide, so the share of the body made up of lean mass went up.

That said, I plan to get another scan at the 12-month mark. I want to see whether the muscle loss rate slows as I approach a maintenance dose and my deficit shrinks. I’ll post those results here.

Should You Get a DEXA Scan on Mounjaro?

If you can access one at a price that works for you, I think so. Here’s why it’s worth it beyond curiosity.

The scale tells you nothing about composition. A person who loses 30 lbs but 40% of it is muscle is in a different situation than someone who loses 30 lbs with 85% fat loss. Same number on the scale, very different outcomes.

DEXA also gives you a baseline visceral fat measurement, which is genuinely useful for tracking metabolic risk that your doctor doesn’t routinely measure.

The one caveat: don’t get a DEXA scan and then become paralyzed by the lean mass number. Some lean mass loss during significant fat loss is expected. Do not stop or change your medication based on a scan without talking to your prescriber. The goal is to minimize it, not eliminate it, and to understand your full composition picture rather than focusing solely on the scale.

The Mounjaro dosage guide covers the standard dose steps. And if you’re still figuring out which medication or provider to start with, the GLP-1 side effects guide gives an honest picture of what to expect beyond just the weight loss numbers.

Bottom Line

After six months on Mounjaro (10mg), I lost 41 lbs total: 35.3 lbs of fat and 5.5 lbs of lean mass. That’s about 13.4% of my weight loss as lean mass, compared with about 25% in the SURMOUNT-1 DEXA substudy. Visceral fat dropped from 187 cm² to 94 cm², which is the result I’m most focused on for long-term health.

Muscle loss on Mounjaro is real but manageable. Resistance training and adequate protein may have helped in my case. A DEXA scan before and during treatment is a practical way to see what is happening inside the weight you are losing.

If you’re trying to find a provider to get started on Mounjaro, the provider directory compares current options on cost, access, and what’s included.

FAQ

How much muscle do you lose on Mounjaro? In the SURMOUNT-1 DEXA substudy, about 25% of the weight lost on tirzepatide was lean mass. Individual results vary, and protein intake and resistance training may affect the ratio.

Is a DEXA scan worth it for tracking Mounjaro results? Yes, if you can access one affordably. DEXA is the most practical way to track the fat-versus-muscle breakdown of your weight loss. The scale can’t tell you whether you’re losing fat or lean mass. Prices vary by area, so call local clinics, and use the same machine each time for comparable results.

Does Mounjaro cause more or less muscle loss than Ozempic? We do not know. The SURMOUNT-1 and STEP 1 DEXA substudies used different methods and populations, so their lean mass shares (about 25% and about 40%) cannot be compared directly. SURMOUNT-5, the head-to-head trial published in NEJM in 2025, found more weight loss with tirzepatide (20.2%) than with semaglutide (13.7%) at 72 weeks, but it did not report DEXA body composition.

Can you prevent muscle loss on Mounjaro? You may be able to reduce it. Resistance training and enough protein are the two steps most often recommended. Ask your prescriber or a dietitian for a protein target, especially if you have kidney disease. You likely won’t achieve zero lean mass loss during aggressive fat loss, but you can shift the ratio substantially in your favor.

How often should I get a DEXA scan on Mounjaro? Every six months is a reasonable interval for most people. That’s enough time for meaningful changes to accumulate, and frequent enough to catch a trend early if lean mass loss is higher than expected. If you’re also monitoring bone density, your doctor may have specific timing recommendations.

Safety note

Mounjaro carries a boxed warning about thyroid C-cell tumors and should not be used by people with a personal or family history of medullary thyroid carcinoma or MEN 2. The label also lists risks including pancreatitis, gallbladder disease, and kidney injury from dehydration. Follow your prescriber’s dosing plan.

What we checked

This AI-assisted public-source desk check reviewed the SURMOUNT-1, STEP 1 and SURMOUNT-5 trial publications, the SURMOUNT-1 and STEP 1 DEXA substudy results, and the Mounjaro label on DailyMed on November 4, 2026. The personal scan numbers are the author’s own and were checked only for internal arithmetic. This is not a clinical review and it is not medical advice. Prices and policies change, so confirm them with the provider or your prescriber before you act.

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