GLP-1 muscle loss and protein

What trials measured

• Tirzepatide. In a SURMOUNT-1 substudy of 160 people, those on tirzepatide lost 21.3% of their weight over 72 weeks, with fat down 33.9% and lean mass down 10.9%. On placebo, the figures were 5.3%, 8.2% and 2.6%. About 75% of the loss was fat and 25% lean mass in both groups.
• Semaglutide. The joint advisory reports that in a STEP 1 substudy, of 13.6 kg lost, 62% was fat and 38% lean mass. We read this figure in the advisory and not in the trial report.

These studies are separate and do not compare the two medicines. The Wegovy and Zepbound labels both describe greater fat loss than lean loss. Lean mass also includes water and organs, and the advisory estimates about 20% of weight lost is muscle.

Protein

The advisory proposes 1.2 to 1.6 g per kg of body weight a day during active weight reduction, compared with the general recommendation of 0.8 g. It notes there is no agreement on which body weight to use, and that an absolute 80 to 120 g a day is another approach. It advises against going below 0.4 to 0.5 g per kg, or staying at 2 g per kg or more for long. If you have kidney disease, ask your prescriber before raising your protein. Try the free protein estimate.

• Eat protein first in a meal.
• Choose small-volume sources: fish, eggs, Greek yogurt, cottage cheese, nuts and seeds.

For meals built around protein, see our high-protein recipes, or get them as a free PDF.

Strength training

The advisory says protein alone is likely inadequate without structured resistance training. It suggests strength work at least 3 times a week, plus at least 150 minutes of moderate aerobic activity, tailored to you. Start where you are, and ask your care team if you have a health condition.

For meal ideas, see what to eat on a GLP-1. If you are also shedding hair, read GLP-1 hair loss. The weight loss calculator shows the average weight change in the trials.

Who should pay most attention

The advisory names older age, menopause, low testosterone and an inactive life as raising the risk of muscle loss. On bones, the Wegovy label reports more hip and pelvis fractures in women in its cardiovascular trial, 1% against 0.2%, and in people aged 75 or older, 2.4% against 0.6%. Ask your prescriber whether body composition or strength checks make sense for you.

How Reko helps

Log protein, weight, body measurements and training together. Reko keeps your symptoms beside your doses, so you can show your prescriber when something began and how it changed. It does not tell you what a symptom means, and it never suggests a dose.

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Questions people ask

Do GLP-1 medicines cause muscle loss?

Lean mass falls along with weight, including on placebo. In a SURMOUNT-1 substudy, about a quarter of the weight lost was lean mass, which also includes more than muscle.

How much protein should I eat on a GLP-1?

A 2025 joint advisory proposes 1.2 to 1.6 g per kg of body weight a day during active weight reduction, and notes there is no agreement on which body weight to use. Ask your care team what fits you.

Is protein enough to protect muscle?

The advisory says protein alone is likely inadequate without structured resistance training.

How often should I do strength training on a GLP-1?

The advisory suggests at least 3 times a week, plus at least 150 minutes of moderate aerobic activity, tailored to you.

Is losing some muscle avoidable?

Trials show lean mass falls with weight in both groups, including on placebo. The advisory treats protein and strength training as ways to reduce the loss.

Which is better for muscle, semaglutide or tirzepatide?

These studies are not head-to-head, so their figures should not be used to compare the two.

Reko records what you and your prescriber decide. This guide is general information and not medical advice.

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Recipes to try

These are ordinary recipes and do not treat any side effect.

Useful tools