GLP-1 muscle loss: what the trials found and how to keep your muscle
In the main semaglutide and tirzepatide trials, lean mass made up about 25% to 38% of the weight people lost. Four major obesity and nutrition groups now pair these drugs with strength training and enough protein to protect muscle.
Book a free Baseline SessionWhere the lost weight comes from, and how to hold on to muscle
Weight comes off fast on a GLP-1 drug such as Ozempic, Wegovy or Zepbound. For people over 40, the next worry follows close behind: how much of the loss is muscle? Many already feel muscle slipping before any prescription. One woman close to 50 described feeling strength leave her legs and arms year by year.
The trials measured this with body scans. In STEP 1, the main semaglutide trial, people lost an average of 13.6 kg, of which 8.3 kg was fat and 5.3 kg, or 38%, was lean mass, according to a 2025 joint advisory from four medical societies. In SURMOUNT-1, a tirzepatide trial, about 75% of the weight lost was fat and 25% was lean mass. The placebo group, which lost far less, showed the same split.
Lean mass is a broad bucket. The term counts water, organs and bone along with muscle. The advisory estimates muscle at about half of lean mass, which puts muscle near 20% of the weight lost in STEP 1. A 2026 review in Nutrients adds a caution: lean mass loss mostly follows the size of the weight loss and is no direct measure of muscle loss or drug damage to muscle. The same review flags older adults as the group with the least muscle to spare.
The fix the experts name is lifting. The joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society says GLP-1 drugs should come with a structured exercise program: strength training at least three times a week plus at least 150 minutes of moderate aerobic exercise. A 2021 trial in the New England Journal of Medicine tested the pairing with liraglutide, an older GLP-1. People on the drug plus exercise cut their body fat percentage about twice as much as people on either one alone.
Protein is the other half. The advisory lists targets proposed during active weight loss, such as 1.2 to 1.6 g per kilogram of body weight a day, or 80 to 120 g a day. Sessions does not prescribe or comment on medication and does not set protein targets. Follow your prescriber on the drug, and ask your doctor or a registered dietitian what protein target fits you.
Plan your training for the long run. In the STEP 1 extension, people regained two thirds of their lost weight within a year of stopping semaglutide and the trial's lifestyle program. If the scale stalls on or off the medication, our post on the weight loss plateau covers how muscle sets the calories you burn. For the longer view, our guide The Truth About GLP-1s and Long-Term Weight Loss goes deeper on long-term weight loss.
How we do this at Sessions. Your first visit is a free Baseline Session: a movement assessment, a 3D body scan, and a written plan you keep whether you join or not. You leave with a starting point beyond the bathroom scale.
From there you follow your own written program, with two coaches on the floor every session and six people per coach. Every set and weight is logged, so each session builds on the last and you never track lifts yourself. Coaches watch form on every set and adjust the weight or swap an exercise on a day you feel off. Membership is month to month, with studios in Santa Monica and Mar Vista. See pricing or book a free Baseline Session.
Three signs your training protects muscle on a GLP-1
- Strength work three days a weekThe joint advisory recommends strength training at least three times weekly alongside GLP-1 treatment.
- Weights climb over timeYour log shows heavier loads or more reps as the weeks pass.
- Your medical team sets the medical partsDose and protein targets come from your prescriber and dietitian, and your coach builds the training around them.
Common questions
Do you lose muscle on Ozempic?
Some, yes. In STEP 1, the semaglutide trial, lean mass made up 5.3 kg of an average 13.6 kg lost, per the 2025 joint advisory. Lean mass includes more than muscle, and the advisory estimates muscle at about 20% of the weight lost. Strength training and enough protein are the recommended ways to limit the loss.
How much of GLP-1 weight loss is muscle?
Lean mass made up about 25% of the weight lost with tirzepatide in SURMOUNT-1 and 38% with semaglutide in STEP 1. Muscle is one part of lean mass, so the muscle share is smaller. Individual results vary.
How do you keep muscle on semaglutide?
Lift weights at least three times a week and add 150 minutes of moderate cardio, per the joint advisory. Eat enough protein, with a target set by your doctor or a registered dietitian. Raise the weights over time so your muscles keep a reason to stay.
Is strength training safe on a GLP-1?
The joint advisory recommends strength training alongside these drugs for most people. Check with your prescriber before you start, especially with a heart condition or recent surgery. Start lighter than you think and tell your coach about side effects such as nausea or dizziness.
What happens if you stop a GLP-1?
In the STEP 1 extension, people regained two thirds of the weight they lost within a year of stopping semaglutide and the lifestyle program. Any decision about stopping belongs with your prescriber. Strength training is a habit you keep either way.
Does Sessions work with people on GLP-1 medication?
Yes. Your coach writes your strength program and logs every lift. Sessions does not prescribe or comment on medication or set nutrition targets. Those decisions stay with your prescriber and a registered dietitian.
Sources: Mozaffarian et al., joint advisory (ACLM, ASN, OMA, TOS), 2025 · Wilding et al., STEP 1, NEJM 2021 · Look et al., SURMOUNT-1 body composition, Diabetes Obes Metab 2025 · Mollero et al., skeletal muscle during incretin therapy, Nutrients 2026 · Lundgren et al., exercise plus liraglutide, NEJM 2021 · Wilding et al., STEP 1 extension, Diabetes Obes Metab 2022