Mounjaro, Ozempic, GLP-1s AND Muscle Health

A patient walked into our HealthSpanMD Andheri clinic last month, three months into Mounjaro, nine kilos lighter, and visibly anxious. She'd read somewhere that GLP-1 drugs "eat your muscles," and she wanted to stop the injections before her body "turned soft." We get a version of this conversation almost every week now, and we understand it. Nobody would take Mounjaro or Ozempic to trade a shrinking waistline for weaker muscles ten years down the line.

It's a fair worry, and it deserves a real answer rather than a reassuring pat on the back. So let's go through what the data actually shows — the big human trials, the newer imaging studies, and some mouse-and-human research published as recently as this year — because the honest picture is more reassuring than the headlines, and more nuanced than the marketing on either side.

Why the Fear Started in the First Place

The scare has a real number behind it. In the original STEP 1 trial, roughly 40% of the weight participants lost on semaglutide (Ozempic) came from what researchers call "lean body mass" (DOI: 10.1056/NEJMoa2032183). SURMOUNT-1, the tirzepatide (Mounjaro) trial, showed a similar pattern — around a quarter to a third of total weight lost showed up as lean soft tissue on the DXA scan (DOI: 10.1056/NEJMoa2206038). Numbers like that, stripped of context and repeated across health blogs, are exactly why our patient was Googling at 11pm.

This is the part that usually gets left out: lean body mass is not the same thing as muscle. It's an umbrella term that includes muscle, yes, but also your organs, bones, body water, and even a lean component of fat sitting inside muscle tissue itself. A 2026 study in Cell Reports Medicine actually measured muscle directly, in mice and in a human pilot trial, and found that liver mass shrank proportionally more than muscle mass did on GLP-1 therapy (DOI: 10.1016/j.xcrm.2026.102665). So when a trial reports "lean mass loss," a meaningful chunk of that number could be your liver shrinking as fatty liver improves, or fat sitting inside and around muscle tissue — not your biceps disappearing. Losing fat from the liver or from inside muscle tissue is, in fact, genuinely good for you.

What "Lean Mass Loss" Actually Contains

This distinction matters a lot clinically. DEXA, the scan most trials rely on, cannot tell the difference between actual contractile muscle and other lean tissue sitting in the same region of your body. A detailed 2024 Circulation review by Linge and colleagues made a case that's changed how we explain this to patients: instead of asking "how much lean mass did I lose," the better question is "did I lose more muscle than expected for the amount of weight I lost" (DOI: 10.1161/CIRCULATIONAHA.124.067676). They use a measure called muscle volume z-score — essentially, comparing your muscle to what's typical for someone your age, sex and body size. Using MRI data from liraglutide and tirzepatide trials, they found these changes were "adaptive," in line with what aging and weight loss alone would predict, rather than a unique drug effect.

A separate 2026 narrative review pulling together 131 studies on this exact question reached a similar conclusion: semaglutide and tirzepatide reduce fat mass — including the dangerous visceral fat around your organs — far more than they reduce lean tissue, and muscle-specific measures such as thigh muscle fat infiltration actually improve, not worsen, on these drugs (DOI: 10.3390/metabo16060364).

A quick side-by-side of what the major trials actually measured makes this clearer:

Does Strength Actually Decline?

This is the question our patients actually care about — not what a scan says, but whether they can still carry their toddler or climb four flights without stopping. And here the data is very reassuring.

A 2025 review in Current Reviews in Musculoskeletal Medicine looked specifically at muscle function rather than just muscle mass, and reported that GLP-1 therapy is associated with reduced muscle fatty infiltration, better fiber formation, and preserved walking-test performance across several studies (DOI: 10.1007/s12178-025-09978-3). The Cell Reports Medicine paper mentioned earlier ran a small human pilot trial and found something similar: ultrasound-measured muscle size dropped modestly, but grip strength and knee-extension strength — actual, measured muscle function — did not decline at all (DOI: 10.1016/j.xcrm.2026.102665). In the same paper's mouse experiments, semaglutide-treated mice actually ran further on a treadmill before exhaustion than untreated obese mice, nearly matching lean control animals. Losing fat weight while preserving muscle improves the muscle-to-bodyweight ratio, and that ratio — not the raw muscle number — is what determines how your body actually performs.

The Mumbai (& India/South Asia) Angle: Why This Still Deserves Caution

None of this means GLP-1 therapy is risk-free for muscle, and we would be doing our patients a disservice if we said otherwise. In our clinical practice, we see a recurring pattern in urban Indian professionals: relatively low baseline muscle mass, a diet leaning heavily on refined carbohydrates, long sedentary commutes, and late dinners — all of which mean many patients start GLP-1 therapy with less muscle reserve than a typical Western trial participant. South Asians as a population also tend to carry more visceral fat and less muscle at any given BMI, which is exactly why we don't treat a "normal" BMI as reassuring on its own when we're assessing someone's metabolic risk.

This is exactly where protein intake and resistance training stop being a "choice" and become mandatory. One striking data point: in a cross-sectional study of current GLP-1 users, only 43% were eating even the minimum recommended 1.2 grams of protein per kilogram of body weight per day, with average intake well below target (DOI: 10.3390/metabo16060364). If appetite suppression is already cutting your food intake and you're not deliberately prioritising protein, that's the scenario where muscle loss can really shift from adaptive to concerning.

Exercise, or some physical activity, or even just a movement, can positively impact every health outcome you desire or possibly name.

— Dr Narendra Rathi

What Actually Protects Your Muscle on GLP-1 Therapy

• check_circleEat protein first at every meal, aiming for roughly 1.2–1.5 g/kg body weight daily, spread across the day rather than loaded into dinner (DOI: 10.3390/metabo16060364)
• check_circleDo resistance training at least twice a week — even two sessions targeting major muscle groups measurably help preserve strength and bone density during weight loss (DOI: 10.3390/metabo16060364)
• check_circleGet your body composition checked periodically, not just your weight — a bioimpedance (BIA) or DEXA scan tells you whether you're losing fat preferentially or losing muscle disproportionately
• check_circleManage nausea and appetite loss actively with your doctor rather than simply eating less of everything, since gut symptoms are usually what quietly wrecks protein intake

When to Actually Worry

At HealthSpanMD, we intensify monitoring — more frequent follow-ups, body composition checks, and sometimes lab work — in a specific subset of patients: those who are older, already have low muscle mass or "sarcopenic obesity," are losing weight unusually fast, or report new weakness, falls, or declining stamina. This risk-stratified approach mirrors the pathway proposed in the 2026 review, which recommends escalating care specifically for poor intake, rapid weight loss, weakness, or bone risk rather than treating every patient the same way (DOI: 10.3390/metabo16060364).

If that's you, this isn't a reason to stop your medication on your own — it's a reason to have this exact conversation with your prescribing doctor.

So, coming back to our original question — is the muscle-loss fear justified? Partly, and it deserves respect rather than dismissal. But the evidence increasingly suggests that for most people, what looks like muscle loss on a DEXA scan is largely fat loss, water shifts, and a shrinking liver, and that the muscle you do lose can be minimised, sometimes even outrun, with two simple habits: eating enough protein, and lifting something heavy twice a week.

What's your experience been — has your strength held up on GLP-1 therapy, or has this been a real concern for you? We'd genuinely like to know.

Key Takeaway

GLP-1 therapy causes real but modest lean-mass loss, and a large share of that reflects liver, water and fat-adjacent tissue rather than contractile muscle. Strength and physical function are largely preserved in the human data available so far, especially when protein intake and resistance training are prioritised. South Asian patients, who often start with lower baseline muscle reserve, should treat these two habits as core therapy rather than optional add-ons. And anyone older, losing weight rapidly, or noticing new weakness should raise it with their doctor rather than adjusting their medication on their own.

FAQs

References

• Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021. DOI: 10.1056/NEJMoa2032183
• Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022. DOI: 10.1056/NEJMoa2206038
• Santic R, et al. Lean Mass and Musculoskeletal Preservation in GLP-1-Based Obesity Treatment. Metabolites. 2026. DOI: 10.3390/metabo16060364
• Gatto A, et al. The Effects of GLP-1 Agonists on Musculoskeletal Health and Orthopedic Care. Curr Rev Musculoskelet Med. 2025. DOI: 10.1007/s12178-025-09978-3
• Linge J, et al. Muscle Mass and Glucagon-Like Peptide-1 Receptor Agonists: Adaptive or Maladaptive Response to Weight Loss? Circulation. 2024. DOI: 10.1161/CIRCULATIONAHA.124.067676
• Langer HT, et al. Weight loss with GLP-1 medicines does not result in a disproportionate loss of muscle mass or function in obese mice and humans. Cell Rep Med. 2026. DOI: 10.1016/j.xcrm.2026.102665

This article is for educational purposes only. It does not constitute healthcare advice, diagnosis, or treatment, and does not establish a doctor-patient relationship. For personalised assessment and guidance on GLP-1 therapy, please book an appointment at HealthSpanMD (www.thehealthspanmd.com).