Protein and Muscle Health During GLP-1 Treatment

What the evidence shows

What Happens to Your Body During Weight Loss

When people lose a significant amount of weight — through any method — the weight that comes off is not made up of fat alone. Some lean tissue is lost as well. This is a normal part of weight loss, and the proportion lost as lean tissue during treatment with these medicines is broadly similar to other substantial weight-loss approaches.^1,3

In studies of incretin-based treatments, most of the weight people lost was fat.^1,3

Lean mass is not the same thing as muscle

You may see the term "lean mass" used in articles about weight loss. It is worth understanding what it actually means.

Lean mass is everything in the body that is not fat. That includes skeletal muscle — the muscle you use to stand, lift and walk — but it also includes water, organs and connective tissue. Body-composition scans do not measure skeletal muscle directly; they estimate it, and part of a reported change can reflect shifts in body water rather than a loss of muscle itself.⁹

This matters because a falling number on a scan is not, by itself, evidence that a person has lost strength or function.^2,3,9

What the evidence does and does not show

Researchers are still working out how much of the lean tissue change during incretin treatment represents skeletal muscle, and what it means for how people actually feel and move. The available evidence does not establish that these medicines cause a disproportionate loss of muscle.^1,3

Measures that matter to daily life — strength, walking, getting out of a chair, carrying shopping — have been studied less often in these trials than weight and scan results have. Where strength has been measured, it did not decline.^1,2,3

The goal is not to protect a number on a scan. The goal is to come through weight loss strong, well-nourished and able to do the things you need to do.

Beyond protein

Muscle Health Is Bigger Than Protein

Protein gets most of the attention in conversations about muscle during weight loss. It deserves some of it. But protein on its own is not the whole picture, and treating it as though it were can lead people to focus on the wrong thing.

Using your muscles matters, too

In the wider weight-loss research — studies not specific to GLP-1 medicines — resistance activity has been studied for its role in helping people hold on to strength and physical function while losing weight. This means activity that asks your muscles to work against resistance: body weight, bands, weights, or everyday tasks that involve lifting and carrying.^4,5

This evidence comes from general weight-loss and older-adult research rather than from trials of incretin medicines specifically. That distinction is worth keeping in mind — it is reasonable evidence, but it was not gathered in people taking these treatments.

Protein and activity work together

Eating protein gives the body the raw material. Using your muscles gives it a reason to keep them. In one study of older adults losing weight, neither higher protein alone nor exercise alone made a clear difference to lean tissue — only the two together did. Looking at them together may be more useful than concentrating on protein alone.⁴

The rest of the picture

• Eating enough overall — not only enough protein
• Sleep and recovery
• Your other medical conditions and medicines
• How well you are tolerating treatment day to day

This guide does not set out an exercise programme. What kind of activity is appropriate, and how much, depends on your health, your fitness and any conditions you live with. That is a conversation to have with your clinician.

Protein matters. Using your muscles matters too. The evidence supports thinking about them together rather than focusing on either one alone.

Eating during treatment

Why Eating Enough Can Become Harder

These medicines work in part by reducing appetite. That is the point of the treatment, and for many people it is exactly what helps. But the same effect can make it genuinely harder to eat well — and that is a practical problem worth planning for rather than a sign that something has gone wrong.

What people may notice

• Feeling full much sooner than expected
• Little or no appetite at usual mealtimes
• Nausea, particularly in the early weeks or after a dose increase
• Food losing its appeal
• Meals becoming smaller without any deliberate decision

These effects are well described in studies of these medicines.^2,8

None of this means you are undernourished. It does mean that eating well now takes more thought than it did before — because the appetite signals that used to organise your eating are quieter.

When to contact your clinician

Some symptoms need clinical attention rather than self-management. Contact your clinician if you experience:

Do not change how you take your medicine on your own. If symptoms are making treatment difficult, that is a conversation to have with the clinician who prescribed it.

About MyoGuard

MyoGuard Protocol is a physician-led Clinical Decision Support platform, designed to be used by clinicians alongside their own judgement when caring for people on GLP-1 and related treatments.

The Sarcopenia Risk Index (SRI) is a physician-led Clinical Decision Support tool that helps clinicians consider factors associated with vulnerability to sarcopenia and muscle compromise during treatment.

It is not a diagnosis. It does not predict what will happen to any individual. It supports clinical judgement rather than replacing it, and every output is interpreted by the treating clinician.

Important

This guide is general education. It is not medical advice, it is not a diet plan, and it does not create a clinician–patient relationship. Decisions about your treatment, your diet and your health belong with you and your own clinician.

References

1. Look M, Dunn JP, Kushner RF, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study. Diabetes Obes Metab. 2025;27(5):2720-2729. DOI 10.1111/dom.16275. PMID 39996356.
2. Alissou M, et al. Impact of semaglutide on fat mass, lean mass and muscle function: the SEMALEAN study. Diabetes Obes Metab. 2026;28(1):112-121. DOI 10.1111/dom.70141. PMID 41068996.
3. Laverde LP, Muñoz-Velandia OM, Alfonso D, Gómez Medina AM. Effect of GLP-1 receptor agonists at doses for obesity management on muscle health. Int J Obes. 2026;50(8):1638-1646. DOI 10.1038/s41366-026-02118-y. PMID 42321502.
4. Verreijen AM, Engberink MF, Memelink RG, et al. Nutr J. 2017;16:10. DOI 10.1186/s12937-017-0229-6. PMID 28166780.
5. Villareal DT, Aguirre L, Gurney AB, et al. N Engl J Med. 2017;376(20):1943-1955. DOI 10.1056/NEJMoa1616338. PMID 28514618.
8. Karrar HR, et al. Tirzepatide-induced gastrointestinal manifestations: a systematic review and meta-analysis. Cureus. 2023;15(9):e46091. DOI 10.7759/cureus.46091. PMID 37908927.
9. Baglietto N, Vaquero-Cristóbal R, Albaladejo-Saura M, et al. Front Nutr. 2024;11:1445892. DOI 10.3389/fnut.2024.1445892. PMID 39224178.