How Much Muscle Do You Lose on a GLP-1? What the Research Shows

How much muscle do you lose on a GLP-1? In the major trials that scanned people's bodies, lean mass made up roughly 25% to 40% of the weight lost on GLP-1 medications. Fat made up the rest. But lean mass isn't the same as muscle. It also includes water, organs and other non-fat tissue, and muscle is only about half of it. In one large semaglutide trial, experts estimate that about 20% of the weight lost was muscle.

You may have seen a headline claiming that 40% of GLP-1 users lose muscle. That's not what the research shows. The figure describes a share of the weight lost, not a share of people. And some lean mass loss comes with almost any large weight loss, whatever the method.

Here's what the studies found about GLP-1 muscle loss, who may be more affected, what helps and what's still unknown.

What Lean Mass Actually Includes

Body composition studies often use DXA, a low-dose X-ray scan that separates the body into fat, bone and lean tissue. Lean mass sounds like muscle, but it's a broader category. A 2024 review points out that it includes not only muscle but also organs, fluids and even the water held inside fat tissue.

The 2025 joint advisory on nutrition and GLP-1 therapy, from four nutrition and obesity medicine organizations, estimates that muscle is about half of lean body mass. So a drop in lean mass on a scan doesn't mean the same amount of muscle is gone.

What the Body Composition Studies Found

The numbers vary, but the pattern is consistent: most of the weight lost is fat, and a meaningful minority is lean mass.

STEP 1 and SURMOUNT-1

In the STEP 1 trial, adults taking semaglutide lost an average of 14.9% of their body weight over 68 weeks. According to the advisory's summary of the trial's body scans, about 62% of the weight lost was fat and 38% was lean mass: roughly 18 pounds of fat and 12 pounds of lean mass out of about 30 pounds lost. With muscle at about half of lean mass, that's roughly 20% of the total.

In a body composition substudy of SURMOUNT-1, 160 adults had DXA scans before and after 72 weeks. People taking tirzepatide lost 21.3% of their body weight, and about 75% of that was fat and 25% lean mass. The placebo group, who also received lifestyle guidance, lost far less weight but in the same 75/25 split. That split stayed fairly consistent across most subgroups, including men, women and adults 65 and older.

Pooled Results From Many Trials

A 2024 network meta-analysis of 22 randomized trials found that tirzepatide and semaglutide led to the most weight and fat loss but were among the least effective at preserving lean mass, while liraglutide lowered weight without a significant drop in lean mass. To explain the wide range, reviewers point to differences in the people studied, the medication, other health conditions and, according to a 2026 review of tirzepatide studies, how body composition was measured.

How This Compares With Other Ways of Losing Weight

Lean mass loss isn't unique to GLP-1 medications. The advisory notes that losses of fat, lean mass and muscle rise with the amount of weight lost and are similar to those seen with bariatric surgery and very low-calorie diets.

• Diet and lifestyle programs: A long-cited rule of thumb holds that about a quarter of the weight lost through dieting is fat-free mass, though a 2014 review notes the real share shifts with age, inactivity and exercise. In a 2026 meta-analysis of 20 trials, lifestyle programs alone had a lean share of about 26%, comparable to GLP-1 medications.
• Bariatric surgery: A meta-analysis of 59 studies found people lost more than 8 kilograms (about 18 pounds) of lean body mass in the first year after surgery, more than half of it in the first three months.
• Lifestyle plus resistance training: In the 2026 meta-analysis, programs that added resistance training had the lowest lean share, about 17.5%.

These figures come from different trials, so treat them as rough guides, not head-to-head results.

Muscle Quality: What MRI Studies Show

Muscle size is only part of the picture. In obesity, extra fat can build up inside muscle, which is linked to more cardiovascular risk factors. A few MRI studies have looked at this:

• Tirzepatide: In a post hoc analysis of the SURPASS-3 trial in 246 adults with type 2 diabetes, thigh muscle volume shrank over 52 weeks, broadly in line with what researchers expected for the weight lost. Fat inside the muscle dropped more than expected. At the highest dose, though, one size-adjusted muscle measure fell more than expected.
• Liraglutide: In a 40-week randomized trial of 128 adults without diabetes, mostly women, thigh muscle fat fell slightly compared with placebo.

A 2024 review in Circulation concluded that muscle changes on GLP-1 medications appear to be adaptive: muscle volume drops roughly as expected for the weight lost, and muscle quality may improve. Read that with care. These were small, fairly short analyses, the SURPASS-3 analysis was funded by the medication's maker, and a better-looking scan doesn't prove better strength or function.

Who May Be at Higher Risk of GLP-1 Muscle Loss

A 2026 review notes that effects on muscle depend on age, starting muscle reserve, nutrition and physical activity. The advisory says low protein intake from a reduced appetite may add to muscle loss and the risk of sarcopenia (low muscle mass and strength), particularly in people who:

• Are older
• Are in perimenopause or past menopause
• Have lower testosterone
• Spend most of the day sitting
• Don't do resistance or strength training

Older adults deserve extra attention. The Circulation reviewers note that older age and prefrailty may affect who is a good candidate for these medications. A 2026 review of muscle strength found that grip strength generally held steady in short- to medium-term trials, but some longer-term observational studies of older adults with type 2 diabetes reported declines with prolonged semaglutide use. If this sounds like you, ask your prescriber about checking your strength and body composition during treatment.

What the Evidence Says Helps

Much of this evidence comes from diet-based weight loss rather than GLP-1 trials, but these steps have the strongest support.

Strength Training

Resistance training has the best evidence. In the 2026 meta-analysis, programs that included it had a lean share of about 17.5%, compared with about 26% for lifestyle programs alone. The advisory calls structured strength training well established to help preserve lean mass during weight loss, while aerobic exercise alone has a smaller effect. It recommends strength training at least three times a week plus at least 150 minutes of moderate aerobic activity, adjusted to your fitness level.

New to lifting? Our beginner's guide to keeping muscle on a GLP-1 has a simple eight-week plan, and strength training basics for GLP-1 weight loss covers form and equipment.

Enough Protein

A meta-analysis of 20 randomized trials in adults over 50 found that people on higher-protein diets kept more lean mass and lost more fat while losing weight. The advisory notes that targets of 1.2–1.6g of protein per kilogram of body weight a day have been proposed during active weight loss, with 80–120g a day as a simpler goal. It also stresses that more protein alone likely isn't enough without strength training. Our guide to protein on a GLP-1 has easy ways to reach your number.

A Steady Pace: The Evidence Is Mixed

The advisory lists how sharply calories are cut and how fast weight comes off among the factors that affect lean mass loss. But a 2020 meta-analysis comparing gradual and rapid weight loss of the same total amount found no significant difference in fat-free mass, though gradual loss led to more fat loss. The takeaway is modest: don't try to speed things up by skipping meals, and follow the dosing plan your prescriber sets.

What Researchers Still Don't Know

• Strength and daily function. In STEP 1, people taking semaglutide reported a bigger improvement in physical functioning than those on placebo. But the 2026 review of tirzepatide studies found they didn't assess function, and the 2026 muscle health review notes that data in older adults remain limited.
• The long term. The trial data above cover about one to one and a half years. The advisory warns that on-and-off use with weight regain may make muscle and bone loss worse without structured nutrition and exercise.
• How well exercise and protein work alongside these medications. Trials are now testing this directly. One published trial protocol describes assigning 232 adults starting semaglutide or tirzepatide to resistance exercise, extra protein, both or neither for six months.

Where Preserve Fits

Strength training and protein-rich meals come first. On days when a full meal feels like too much, a light drink can be easier to manage. auravi made Preserve for those days. Each scoop of the tropical punch drink mix has 5,000mg of essential amino acids, 3,000mg of creatine monohydrate and 1,500mg of HMB.

Preserve helps maintain lean muscle while you lose weight, alongside strength training and enough protein.* It isn't a meal or protein replacement. For the research on one of its ingredients, see our article on creatine on a GLP-1. Check with your prescriber before adding any supplement.

Frequently Asked Questions

Do 40% of GLP-1 Users Lose Muscle?

No. In STEP 1, about 38% of the weight people lost was lean mass, which includes water and organs as well as muscle. The figure describes how weight loss broke down on average, not how many people lost muscle.

Does Losing Lean Mass Mean I'm Getting Weaker?

Not necessarily. Grip strength has generally held steady in short- to medium-term trials, and STEP 1 participants on semaglutide reported a bigger improvement in physical functioning than those on placebo. Longer-term data are limited. If stairs or getting up from a chair start to feel harder, tell your prescriber.

Is Muscle Loss Worse on a GLP-1 Than With Dieting?

Current evidence suggests the share of weight lost as lean mass is broadly similar to lifestyle programs and bariatric surgery. Because GLP-1 medications often lead to more weight loss, the total amount of lean mass lost can be larger. Strength training plus enough protein is the best-supported way to keep more of it.

Sources

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3. Look M et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab. 2025.
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5. Eisa N, Barood O. Lean mass changes with incretin therapy versus lifestyle intervention: a systematic review and meta-analysis of randomised controlled trials. Diabetes Obes Metab. 2026.
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7. Wilkinson T, Ramzan R. Beyond weight loss: a narrative review of tirzepatide's impact on muscle and lean mass in people with overweight and obesity. Curr Med Res Opin. 2026.
8. Heymsfield SB et al. Weight loss composition is one-fourth fat-free mass: a critical review and critique of this widely cited rule. Obes Rev. 2014.
9. Nuijten MAH et al. The magnitude and progress of lean body mass, fat-free mass, and skeletal muscle mass loss following bariatric surgery: a systematic review and meta-analysis. Obes Rev. 2022.
10. Sattar N et al. Tirzepatide and muscle composition changes in people with type 2 diabetes (SURPASS-3 MRI): a post-hoc analysis of a randomised, open-label, parallel-group, phase 3 trial. Lancet Diabetes Endocrinol. 2025.
11. Pandey A et al. Effect of liraglutide on thigh muscle fat and muscle composition in adults with overweight or obesity: results from a randomized clinical trial. J Cachexia Sarcopenia Muscle. 2024.
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13. Mollero ELM et al. Beyond weight loss: skeletal muscle health during incretin-based therapy in patients with diabesity. Nutrients. 2026.
14. Prokopidis K. Glucagon-like peptide-1 receptor agonists and muscle strength changes in older adults: risks beyond muscle mass reductions. Br J Pharmacol. 2026.
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16. Ashtary-Larky D et al. Effects of gradual weight loss v. rapid weight loss on body composition and RMR: a systematic review and meta-analysis. Br J Nutr. 2020.
17. Alawadhi AA et al. LEAN mass Preservation with Resistance Exercise and Protein during semaglutide and tirzepatide therapy (LEAN-PREP study): a protocol for a randomised controlled trial. BMJ Open. 2026.

This article is for educational purposes only and is not medical advice. Talk with your healthcare provider before changing your diet, exercise or supplement routine, especially while taking a GLP-1 medication. *These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.