How to keep muscle on a GLP-1

How much lean mass people lose on tirzepatide

The best data we have comes from a DXA substudy of 160 people in SURMOUNT-1, the main Zepbound trial in adults without diabetes ^[1]. DXA is the scan that splits body weight into fat and lean tissue.

Body composition change at week 72 in the SURMOUNT-1 DXA substudy

Measure	Tirzepatide	Placebo
Body weight	Down 21.3%	Down 5.3%
Fat mass	Down 33.9%	Down 8.2%
Lean mass	Down 10.9%	Down 2.6%

The split of about 25% lean and 75% fat held across most subgroups, including men and women, age groups, and people who lost more or less weight ^[1]. For the full trial results, see tirzepatide results.

What we could not confirm for semaglutide

We do not yet have a checked body composition figure for semaglutide. Figures from the STEP 1 trial's DXA scans are widely repeated, but we could not check them against the original paper before publishing, so we leave them out. What STEP 1 does show: adults on semaglutide 2.4 mg lost an average of 14.9% of body weight at 68 weeks, vs 2.4% on placebo ^[3]. In SURMOUNT-5, the head-to-head trial, average weight change at 72 weeks was 20.2% with tirzepatide and 13.7% with semaglutide ^[4]; we did not find body composition results from that trial in our sources. See semaglutide results and Wegovy vs Zepbound.

Protein and strength training: what is confirmed

The Zepbound and Foundayo labels approve each drug for use with a reduced-calorie diet and increased physical activity ^[5][6]. Neither label sets a protein target or an exercise program.

We tried to confirm the protein amounts and resistance-training advice in a 2025 joint nutrition advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society. We could not reach the document on Oct 17, 2026, so we are not printing its numbers. We will add them once checked. Until then, these steps rest only on facts we could confirm:

• Ask your prescriber or a registered dietitian for a protein target that fits your health and any kidney or other conditions you have.
• Ask whether a body composition scan before and during treatment makes sense for you. A DEXA scan at BodySpec starts at $39.95 per scan, checked Oct 17, 2026 ^[7]. Prenuvo lists an MRI-based body composition analysis at $499 ^[8]. See DEXA scan cost.
• Ask your clinician before starting a new strength program if you have heart, joint or other health conditions.
• Tell your prescriber if nausea or poor appetite keeps you from eating regular meals. The label warns about severe stomach and gut reactions ^[2].

Side effects that make eating enough harder

Appetite loss and stomach effects can make it hard to eat enough. In Mounjaro's diabetes trials, decreased appetite was reported by 5% to 11% of people on 5 mg to 15 mg, vs 1% on placebo ^[9]. On Zepbound, nausea affected 25% to 29% across doses, vs 8% on placebo ^[2]. On Wegovy 2.4 mg, nausea affected 44% and vomiting 24%, vs 16% and 6% on placebo ^[10].

Both labels warn of acute kidney injury from fluid loss, which can follow vomiting or diarrhea ^[2][10]. Read our GLP-1 side effects guide and GLP-1 diet plan for more.

Coming off a GLP-1

Weight tends to come back after stopping. In SURMOUNT-4, people lost an average of 20.9% on tirzepatide over a 36-week lead-in. From week 36 to 88, those switched to placebo regained 14.0% while those who stayed on tirzepatide lost another 5.5% ^[11]. In the STEP 1 extension, people regained 11.6 of the 17.3 percentage points they had lost within a year of stopping semaglutide ^[12].

We found no data in our sources on how much of the regained weight is lean mass or fat. Our guides to stopping tirzepatide and stopping semaglutide (and stopping Mounjaro) cover what the labels say. For all treatment options, start at our weight loss guide.