Yes, people on GLP-1 drugs lose some muscle along with fat. In the original semaglutide trial’s body-scan substudy, close to 40% of the weight lost was lean mass; with tirzepatide it was roughly a quarter. But “lean mass” is not the same as muscle, any large weight loss costs some lean tissue, and muscle quality often improves as fat inside the muscle shrinks.
What matters is that you can tip the balance. The two levers with the strongest evidence are resistance training and enough protein. Creatine, pacing the weight loss, and sleep help further. And drug makers are now testing add-ons: in the 2025 BELIEVE trial, adding the antibody bimagrumab to semaglutide cut the share of weight lost as lean mass from about 28% to about 7%. Here is the complete, practical guide.
Why weight loss costs muscle
Whenever you eat less energy than you burn, your body draws on stored fuel. Most comes from fat, but some comes from lean tissue, because muscle protein is constantly being broken down and rebuilt, and in an energy deficit rebuilding slows. Without a strong reason to keep muscle (lifting, enough protein), the body lets some of it go.
This is not unique to GLP-1 drugs. Typical diet-only weight loss also costs lean mass, often in the range of a fifth to a third of the total. GLP-1 drugs make the issue bigger for two reasons: the weight loss is larger and faster, and appetite drops so much that many people under-eat protein without realizing it.
What the GLP-1 body-scan data show
Trials measured body composition with DEXA scans in subgroups of participants.
| Trial | Drug | Total weight loss | Share of loss that was lean mass |
|---|---|---|---|
| STEP 1 DEXA substudy | Semaglutide 2.4 mg | About 15% | Close to 40% |
| SURMOUNT-1 DEXA substudy | Tirzepatide | About 21% (top dose) | Roughly a quarter |
| BELIEVE (2025), semaglutide arm | Semaglutide 2.4 mg | 15.7% | About 28% |
| BELIEVE, semaglutide + bimagrumab | Combination | 22.1% | About 7% |
Two caveats. First, these are small subgroups, and numbers vary between studies. Second, real-world patients often train less and eat less protein than trial participants, so losses may be larger outside trials. A 2025 real-world analysis even suggested tirzepatide users lost slightly more lean mass than semaglutide users, likely because they lost more weight overall.
Lean mass is not the same as muscle
DEXA’s “lean mass” includes everything that isn’t fat or bone: muscle, but also water, organs, skin and connective tissue. Some of the lean mass “lost” is simply less water and smaller organs supporting a smaller body. MRI studies suggest the true muscle loss is meaningful but smaller than headline lean-mass numbers imply, and that muscle quality can improve as fat infiltration within muscle falls.
So the honest framing is: the concern is real, especially for some people, but it is manageable, not a reason to avoid treatment that improves health.
Who should worry most
- Adults over 60, who already lose muscle with age (sarcopenia) and have more to lose in function and fall risk.
- People with low muscle to begin with, including “skinny-fat” body types.
- Postmenopausal women, who lose muscle and bone faster.
- People losing weight very fast or eating very little.
- People with diabetes, in whom muscle is a major site of glucose disposal.
Signs you’re losing too much muscle
- Strength dropping in the gym, or daily tasks (stairs, carrying groceries, getting up from the floor) getting harder
- Feeling weak or shaky, beyond normal early-treatment fatigue
- A “deflated” look in arms and legs rather than just a smaller waist
- Slower walking speed or worse balance
- Grip strength falling (easy to track with an inexpensive dynamometer)
The protection scorecard
| Strategy | Evidence | Impact |
|---|---|---|
| Resistance training 2–3x/week | Strong | Highest |
| Adequate protein | Strong | High |
| Slower rate of loss | Moderate | Moderate |
| Creatine | Moderate (stronger with training) | Moderate |
| Sleep 7–9 h | Moderate | Moderate |
| Vitamin D (if low) | Weak-moderate | Low |
| Muscle-preserving drugs (bimagrumab etc.) | Phase 2 trials | Potentially high; not yet approved |
| GH peptides, MOTS-c | Animal / limited human | Unknown; research only |
Resistance training: the non-negotiable
Muscle is kept when it is used against resistance. Trials of diet-induced weight loss in older adults consistently show that adding resistance training preserves lean mass and strength far better than diet alone or diet plus walking. GLP-1 medicine specialists now treat strength training as part of the prescription.
A simple, effective template
- Frequency: 2 to 3 full-body sessions per week.
- Movements: a squat or leg press, a hinge (deadlift variation or hip thrust), a push (push-up, bench or overhead press), a pull (row or pulldown), plus carries or core work.
- Effort: sets of about 6 to 15 reps, finishing each set with only a couple of reps left in the tank.
- Progression: add weight or reps gradually. Maintaining strength while losing weight is a win; gaining is a bonus.
Nausea and fatigue are common in the first weeks and after dose increases. On rough days, do a shorter session with fewer sets rather than skipping completely. Train when you feel best, often before the day’s first big meal or a few days after your weekly injection when side effects ease.
Protein: how much, and how to hit it with no appetite
During weight loss, many sports and obesity nutrition experts recommend roughly 1.2 to 1.6 grams of protein per kilogram of body weight per day, and some use a reference or goal weight for people with high body weight. That is often double what people on GLP-1 drugs actually eat.
Practical tactics
- Protein first: eat the protein part of each meal before anything else, while appetite lasts.
- Aim for 25 to 40 g per meal across 3 to 4 eating occasions.
- Use dense, easy sources: Greek yogurt or skyr, cottage cheese, eggs, fish, chicken, tofu, lentils, and protein shakes when solid food is hard.
- Liquid protein is often better tolerated when nauseated.
- Avoid large, fatty meals, which slow an already slowed stomach and worsen nausea.
People with kidney disease should check protein targets with their clinician.
Creatine and other supplements
- Creatine monohydrate is one of the best-studied supplements in existence. Combined with resistance training, it increases strength and lean mass, including in older adults. A small water-weight gain is normal.
- Leucine-rich protein (whey) stimulates muscle protein synthesis efficiently per gram.
- HMB: modest, inconsistent evidence.
- Vitamin D: correct if deficient; common in Canadian winters.
- Omega-3: small effects on muscle protein synthesis in older adults in some studies.
Pacing the weight loss
Faster weight loss tends to cost proportionally more lean mass. Many clinicians aim for roughly 0.5 to 1% of body weight per week once established. If you’re losing much faster, struggling to eat, or getting weaker, that’s worth raising with your prescriber; dose escalation can sometimes be slowed.
Sleep, hormones and recovery
Muscle repair and growth hormone release happen largely during deep sleep, and short sleep in a calorie deficit shifts weight loss away from fat toward lean tissue in controlled studies. Weight loss itself often improves sleep apnea, which helps recovery. In men, significant weight loss tends to raise testosterone, which also supports muscle (see low testosterone in Canada).
Bimagrumab and the next wave of drugs
The pharmaceutical industry has recognized the problem, and “quality of weight loss” is now a major research theme.
Bimagrumab
Bimagrumab is an antibody that blocks activin type II receptors, which normally act as brakes on muscle growth (the same pathway as myostatin). In the phase 2b BELIEVE trial presented in 2025, 507 adults with obesity were treated for 72 weeks:
- Semaglutide alone: 15.7% weight loss, with about 28% of it lean mass.
- Bimagrumab plus semaglutide: 22.1% weight loss, with only about 7% of it lean mass, meaning more than 90% of the loss was fat.
- Bimagrumab alone: 10.8% weight loss, essentially all fat.
Eli Lilly is developing it further. It is not approved anywhere yet.
Other approaches
Companies are testing myostatin and activin-pathway blockers, selective androgen receptor modulators, and next-generation incretin drugs designed to spare muscle. Expect results through 2026 and 2027.
Growth hormone peptides and MOTS-c: the research
People researching muscle preservation often encounter several research peptides. Here is where the evidence actually stands.
Growth hormone secretagogues
Ipamorelin, CJC-1295 and tesamorelin stimulate the body’s own growth hormone release. Growth hormone has anabolic effects on muscle and promotes fat breakdown. Tesamorelin is an approved medicine (Egrifta, made by Montreal-based Theratechnologies) for reducing excess abdominal fat in people with HIV-associated lipodystrophy. None of these has been tested in trials for preserving muscle on GLP-1 drugs. Comparison: CJC-1295 vs tesamorelin vs ipamorelin.
IGF-1 LR3
A long-acting analog of insulin-like growth factor 1, the main mediator of growth hormone’s effects on muscle. It is a cell-culture and animal research tool, with significant theoretical risks such as low blood sugar. See IGF-1 vs IGF-1 LR3.
MOTS-c
A peptide encoded by mitochondrial DNA. In older mice, MOTS-c improved physical capacity and muscle function, earning the nickname “exercise mimetic” (Reynolds et al., 2021). Human data are minimal. More in longevity peptides ranked by evidence.
None of these peptides is approved in Canada for muscle preservation, and none has GLP-1 trial data. Resistance training and protein have far stronger evidence. The peptides below are research compounds only.
| Research compound | Research area | From |
|---|---|---|
| Ipamorelin | GH secretagogue | $40 |
| Tesamorelin | GHRH analog | $37 |
| CJC-1295 + Ipamorelin | Combined GH research | $75 |
| MOTS-c | Mitochondrial peptide, exercise capacity (animal) | $55 |
| IGF1-LR3 | Growth factor (cell research) | $15 |
Lab reports are in our COA library.
How to measure what you’re losing
- Strength log: the most practical indicator. If your lifts hold, your muscle is likely holding.
- Grip strength: simple and predictive of health outcomes.
- Waist measurement: tracks fat loss better than the scale.
- DEXA scan: private clinics in Canada offer body-composition DEXA for a fee; useful as a baseline and every few months.
- Bioimpedance scales: convenient but imprecise, and affected by hydration.
Stopping the drug: the muscle trap
Most people regain much of the lost weight after stopping GLP-1 drugs. The risk is regaining it mostly as fat after having lost a share as muscle, leaving body composition worse than before. That is the strongest argument for protecting muscle during treatment, and for keeping up training after any change in medication. See weight loss injections in Canada for more on what happens after stopping.
A sample high-protein day
| Meal | Example | Approx. protein |
|---|---|---|
| Breakfast | Greek yogurt or skyr with berries and a scoop of protein powder | 30–40 g |
| Lunch | Chicken or tofu with vegetables and a small portion of rice | 30–35 g |
| Snack | Protein shake or cottage cheese | 20–25 g |
| Dinner | Salmon or lean beef with potatoes and salad | 30–40 g |
| Total | About 110–140 g |
Portions can shrink as appetite drops; protect the protein portion first.
A 12-week starter strength program
If you have never lifted, this simple progression builds the habit without overwhelming a body that is adjusting to a GLP-1 drug. Machines are fine; so are dumbbells or resistance bands at home. Get clearance from your clinician if you have heart disease, uncontrolled blood pressure or joint problems, and consider a few sessions with a qualified trainer or physiotherapist to learn technique.
| Weeks | Sessions / week | Structure | Goal |
|---|---|---|---|
| 1–2 | 2 | 5 exercises, 2 sets of 10–12, light | Learn movements, no soreness spiral |
| 3–6 | 2–3 | 5–6 exercises, 3 sets of 8–12 | Add weight when the last reps feel easy |
| 7–12 | 3 | 6 exercises, 3 sets of 6–12, alternate heavier and lighter days | Steady progression; track every session |
The core exercise menu
- Legs: goblet squat, leg press, or sit-to-stand from a bench; split squats as you progress
- Hips: hip thrust or glute bridge; Romanian deadlift with dumbbells
- Push: incline push-up, chest press machine, dumbbell overhead press
- Pull: seated cable row, lat pulldown, band rows
- Carry and core: farmer’s carry, plank or dead bug
Add 20 to 30 minutes of walking most days. Walking won’t preserve much muscle on its own, but it helps insulin sensitivity, mood and recovery.
Write down the weight and reps of your main leg exercise every session. If that number holds or rises while the scale falls, you are almost certainly losing fat, not muscle.
Over 60: screening for sarcopenia
Sarcopenia is the age-related loss of muscle mass, strength and function, and it predicts falls, disability and loss of independence. For older adults starting GLP-1 drugs, it’s worth a quick baseline check, ideally with your clinician:
- Grip strength with a hand dynamometer.
- Chair stand test: how many times you can stand from a chair without using your arms in 30 seconds, or how long five stands take.
- Gait speed: time to walk a short, measured distance at a normal pace.
- DEXA for muscle mass when available.
Repeat these every few months. If they decline, prioritize training and protein, and discuss slowing dose escalation. For frail older adults, prescribers may set more modest weight-loss targets, and some specialists pair GLP-1 treatment with supervised exercise programs.
Eating enough protein when you feel sick
Nausea, early fullness and food aversions are the biggest practical barriers to protein on GLP-1 drugs, especially in the first weeks and after each dose increase. Strategies that help:
- Small, frequent portions: 4 to 6 mini-meals instead of 3 large ones.
- Cold and bland: cold foods often smell less and sit better (Greek yogurt, cottage cheese, chilled shakes, cold chicken).
- Sip, don’t gulp: a protein shake over 20 to 30 minutes.
- Avoid greasy, fried and very sweet foods, which slow emptying further.
- Stop at the first sign of fullness: overeating on these drugs is a common cause of vomiting.
- Stay hydrated between meals rather than with them.
- Talk to your prescriber if nausea prevents eating; dose timing or escalation can often be adjusted.
Plant-based protein on a GLP-1
Vegetarians and vegans can absolutely protect muscle, but it takes more planning because plant foods are bulkier and some proteins are lower in leucine, the amino acid that most strongly triggers muscle building.
| Food | Protein (approx.) |
|---|---|
| Firm tofu, 150 g | About 20–25 g |
| Tempeh, 100 g | About 19–20 g |
| Cooked lentils, 1 cup | About 18 g |
| Edamame, 1 cup | About 17–18 g |
| Seitan, 100 g | About 25 g |
| Soy or pea protein powder, 1 scoop | About 20–25 g |
Because appetite is small on GLP-1 drugs, protein powders and soy foods are especially useful: they deliver a lot of protein in little volume. Aim for slightly higher total protein than meat-eaters, and consider creatine, since vegetarians tend to have lower muscle creatine stores and often respond well to it.
Don’t forget bone
Large weight loss also reduces bone density, because bone responds to the load placed on it. That matters most for postmenopausal women and older men. The same tools protect both muscle and bone: resistance and impact training (as tolerated), adequate protein, calcium and vitamin D. Ask whether a bone density scan makes sense if you are older or have other risk factors. Our menopause guide covers bone protection in more detail.
Muscle loss myths
- “GLP-1 drugs destroy muscle.” They cause weight loss, and weight loss costs some lean tissue. Training and protein shift the balance strongly toward fat loss.
- “All lean mass lost is muscle.” Lean mass includes water and organs; true muscle loss is smaller.
- “Cardio protects muscle.” Cardio is good for health, but resistance training is what preserves muscle.
- “You need huge amounts of protein.” Around 1.2 to 1.6 g/kg/day is the commonly recommended range; more brings little extra benefit.
- “Lifting will make you bulky.” In a calorie deficit, lifting mostly preserves muscle and shape; it rarely adds much size.
- “It’s too late after 60.” Strength training improves muscle and function well into the 80s and 90s.
How fast is too fast?
There is no single cut-off, but rate of loss is a useful warning light for muscle. Here is a practical guide many clinicians use once treatment is established:
| Weekly loss (% of body weight) | Interpretation | What to check |
|---|---|---|
| Under 0.5% | Slow but sustainable | Fine if improving; review if goals require more |
| 0.5–1% | Typical target range | Keep protein and training consistent |
| 1–1.5% | Fast | Strength trend, protein intake, energy |
| Over 1.5% sustained | Very fast; higher muscle-loss risk | Discuss dose escalation, eating enough, hydration |
Early weeks often show faster drops from water and glycogen; judge the trend over a month. People starting at higher body weights can safely lose more absolute kilograms per week.
8 common mistakes
- Relying on the scale alone, without tracking strength or waist.
- Skipping meals entirely because there’s no appetite, leading to very low protein.
- Only doing cardio, which does little to preserve muscle.
- Training too little to matter: very light weights with no progression.
- Escalating the dose quickly despite poor eating and fatigue.
- Ignoring hydration, which worsens fatigue, constipation and dizziness.
- Drinking calories as alcohol, which displaces protein and impairs recovery.
- Stopping training after reaching goal, just when muscle matters most for keeping weight off.
The maintenance phase
Once weight loss slows or a goal is reached, the focus shifts from protecting muscle to rebuilding it. Appetite often returns somewhat, which makes it easier to eat enough protein and support training. This is the ideal time to:
- Progress training harder, aiming to gain strength.
- Keep protein high and bring overall calories up to maintenance.
- Reassess body composition with a DEXA scan if available.
- Discuss long-term medication plans with your prescriber, including maintenance dosing.
More muscle raises daily energy expenditure slightly, improves blood sugar control, and makes it easier to maintain the weight you’ve lost.
FAQ
Tap a question to reveal the answer.
Do you lose muscle on Ozempic?
Some. In the semaglutide trial’s body-scan substudy, close to 40% of weight lost was lean mass, though lean mass includes water and organs, not just muscle. Strength training and protein reduce the loss.
Does Zepbound cause less muscle loss than Wegovy?
In trial substudies, a smaller share of tirzepatide weight loss was lean mass (roughly a quarter), but people lose more total weight on it. Real-world data are mixed. Lifestyle matters more than drug choice.
How much protein should I eat on a GLP-1?
Many experts suggest roughly 1.2 to 1.6 g per kg of body weight per day during weight loss, spread across meals. People with kidney disease should check with their clinician.
Can you build muscle on Ozempic?
Beginners, and people returning to training, can often maintain or even gain some muscle while losing fat if they lift consistently and eat enough protein.
What is bimagrumab?
An investigational antibody that blocks activin type II receptors, a brake on muscle growth. In the 2025 BELIEVE trial, combining it with semaglutide produced more weight loss with much less lean mass loss. It is not approved yet.
Do growth hormone peptides prevent muscle loss on GLP-1 drugs?
There are no trials testing that. They are research compounds and not approved for this use in Canada.
Is creatine safe to take with Ozempic?
Creatine is widely considered safe for healthy adults and has no known interaction with GLP-1 drugs. People with kidney disease should ask their clinician first.
How many days a week should I lift weights on Ozempic?
Two to three full-body resistance sessions per week is the standard recommendation, progressing the weight or reps gradually.
Can I preserve muscle on a GLP-1 as a vegetarian?
Yes. Prioritize dense protein sources like tofu, tempeh, lentils and soy or pea protein powder, aim slightly higher on total protein, and consider creatine.
How fast should I lose weight on a GLP-1 to protect muscle?
Many clinicians aim for roughly 0.5 to 1% of body weight per week once treatment is established. Sustained losses above about 1.5% a week raise the risk of muscle loss and deserve a check-in with your prescriber.
Related reading
- Weight loss injections in Canada
- Loose skin after weight loss
- Longevity peptides ranked by evidence
- Retatrutide vs tirzepatide vs semaglutide
References
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1), including DEXA substudy. N Engl J Med. 2021;384:989–1002. PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–216. PubMed
- HCPLive. BELIEVE: bimagrumab plus semaglutide yields substantial fat mass loss, preserves lean mass. June 2025. HCPLive
- European Medical Journal. Tirzepatide linked to more lean mass loss than semaglutide (real-world analysis). EMJ
- Reynolds JC, Lai RW, Woodhead JST, et al. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nat Commun. 2021;12:470. PubMed
This article is general information, not medical advice. Talk to your prescriber before changing diet, exercise or medication. TrueLabs research compounds are sold for in vitro and laboratory research use only and are not intended for human or veterinary use.