Last reviewed: September 2026·Based on 3 clinical trials
Some muscle loss happens with any weight loss. Body scans show that 75–79% of weight lost on newer medications is fat.
Semaglutide (Wegovy)
STEP 1 DEXA
79% fat21% lean
For every 10 lbs lost, about 7.9 lbs was fat and 2.1 lbs was lean tissue
Tirzepatide (Zepbound)
SURMOUNT-1 DEXA
75% fat25% lean
For every 10 lbs lost, about 7.5 lbs was fat and 2.5 lbs was lean tissue
Liraglutide (Saxenda)
SCALE DEXA
75% fat25% lean
For every 10 lbs lost, about 7.5 lbs was fat and 2.5 lbs was lean tissue
Diet + exercise alone
Multiple studies
70% fat30% lean
Typical range is 25–35% muscle loss — medications are in the same range or better
Orforglipron (Foundayo): No body scan data has been published yet. Based on its GLP-1 mechanism, muscle loss is expected to be in a similar range to other GLP-1 drugs.
The medications do not make muscle loss worse than dieting alone. Rapid weight loss itself is the driver — regardless of how you lose it. The GLP-1 drugs actually show equal or better muscle preservation compared to diet and exercise.
What this means in real pounds
For someone starting at 240 lbs, here is what the trial averages look like:
Semaglutide (Wegovy)
Total lost35.8 lbs
Fat lost28.3 lbs
Muscle lost7.5 lbs
Tirzepatide (Zepbound)
Total lost50.2 lbs
Fat lost37.6 lbs
Muscle lost12.5 lbs
Averages from studies. Individual results depend on diet, exercise, starting weight, and genetics.
Drug-by-drug summary
In their own DEXA sub-studies, semaglutide's fat-to-lean ratio was 79% fat / 21% muscle, and tirzepatide's and liraglutide's were each 75% fat / 25% muscle — different trials, not a head-to-head comparison. Tirzepatide's larger total weight loss means more total fat lost, and also more total muscle lost in absolute pounds. Resistance training and adequate protein intake are associated with better muscle preservation during weight loss, regardless of which medication is used.
The two things that actually preserve muscle
Resistance training and protein intake are both associated with better muscle preservation during weight loss, regardless of which medication is used:
Resistance training
2–3 sessions per week
This is the single most effective countermeasure. Lifting weights or bodyweight exercises signal your muscles to hold on to mass, even during a calorie deficit. Studies consistently show this preserves significantly more muscle than cardio or no exercise.
Protein intake
60–100g per day
Protein gives your muscles the building blocks they need to maintain themselves. Aim for 1.0–1.2g per kg of body weight daily. Eat protein first at every meal — this helps especially when your appetite is reduced on medication.
Resistance training and adequate protein intake are associated with better muscle preservation during weight loss. This applies whichever medication — or whether any medication — you're using.
Side effects for your specific medication
Muscle loss varies by drug. See the full side effect profile including body scan data:
→Yes, some muscle loss is unavoidable — but 75–79% of what you lose on medication is fat
→Medications are not worse than dieting — diet alone causes 25–35% muscle loss, the same or more
→Resistance training helps preserve muscle — during weight loss, regardless of which medication you're on
→Muscle loss is not permanent — you can rebuild muscle with consistent strength training after weight stabilises
Based on body scan data from studies, about 21–25% of total weight lost on GLP-1 medications is muscle and other lean tissue (muscle, bone, water). For semaglutide (Wegovy), 79% of weight lost was fat and 21% was muscle. For tirzepatide (Zepbound), 75% was fat and 25% was muscle. The majority of weight lost is fat in all cases.
Not necessarily. You can rebuild muscle with resistance training after weight stabilises. Study data suggests that muscle recovery is possible within 6–12 months of consistent strength training, even while remaining on medication.
Clinical guidance recommends 1.0–1.2g of protein per kilogram of body weight during active weight loss — roughly 60–100g per day for most people. Some experts recommend up to 1.6g/kg. Prioritising protein at every meal helps, especially when appetite is reduced.
Yes. Resistance training combined with adequate protein intake is associated with better muscle preservation during weight loss. This applies regardless of which medication — or whether a medication — is being used.
In their own DEXA sub-studies, semaglutide's ratio was 79% fat / 21% muscle, and tirzepatide's was 75% fat / 25% muscle — separate trials, not a head-to-head comparison. Tirzepatide causes more total weight loss, so the absolute muscle lost is higher even though the ratio is similar. Resistance training is associated with better muscle preservation regardless of which drug is used.
No. Some muscle loss occurs with any significant weight loss — dieting, surgery, or medication. In fact, diet alone typically results in 25–35% muscle loss, which is the same or worse than what GLP-1 drugs show. The health benefits of fat loss far outweigh the modest muscle reduction.
There is no published body scan data for orforglipron yet. Based on its GLP-1 mechanism, muscle loss is expected to be in a similar range to other GLP-1 drugs. The ATTAIN trials focused on total weight loss, not body composition.
In their own DEXA sub-studies, semaglutide (Wegovy) showed a 79% fat / 21% muscle ratio. Tirzepatide (Zepbound) and liraglutide (Saxenda) each showed 75% fat / 25% muscle. These are separate trials, not a head-to-head comparison. Because tirzepatide causes more total weight loss, the absolute muscle lost is higher even at a similar ratio; liraglutide's smaller total weight loss means a smaller absolute amount of muscle lost (about 4.8 lbs for a 240 lb person) alongside its smaller amount of fat lost.
Tirzepatide's DEXA sub-study ratio is 25% muscle; semaglutide's is 21% muscle in its own sub-study. Tirzepatide also causes more total weight loss, and the two figures come from separate trials, not a head-to-head comparison. Resistance training is associated with better muscle preservation regardless of which drug is used.
Written and maintained by one person · Built with agentic AI tools · Every number checked against the cited trial · Not medical advice
Built with agentic AI tools and not a substitute for medical advice
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