GLP-1 · Evidence-based

You're on a GLP-1 and losing weight. But are you losing muscle?

TONE Health · Nutrition & diabetes education · Updated July 2026 · 6 min read

The scale is finally moving. The hunger that followed you for years has gone quiet. And right then, someone says: "careful, you're also losing muscle." Is it true? Should you worry? The honest answer: it's a real risk, and it's largely preventable. Here's what the science says, in plain language.

What almost no one explains when they write the prescription

GLP-1 medications (semaglutide, tirzepatide) work: they produce significant weight loss. But when researchers measured what kind of weight is lost, they found something that changes the plan: in the studies, about 40% of the weight lost can be lean mass (muscle), not fat [1]. And a 2025 finding adds an important twist: losing too much muscle is linked to less improvement in blood sugar control, meaning it subtracts from the medication's own benefit [2].

Sources: STEP 1 trial [1]; ENDO 2025 [2]; STEP 1 extension [3].

Losing some lean mass when you lose a lot of weight is normal. Losing too much means less strength, a slower metabolism, and a higher risk of regaining the weight as fat. And there's a second key finding: in the STEP 1 extension, those who stopped the medication regained about two-thirds of the weight within a year [3]. The people who did best are those who built eating and activity habits during treatment, not instead of it.

Why it happens

These medications drop your appetite dramatically. That's how they work. But when you eat much less overall, you almost always eat much less protein too, and protein is the raw material of your muscle. Add rapid weight loss and less physical activity, and the body starts using muscle as fuel. The 2025 study also found the risk is higher in women and older adults, and that eating more protein helps protect muscle [2].

Five things you can do this week

1. Protein goes first on the plate. When your appetite is small, start with protein. Eggs, fish, chicken, beans with cheese, Greek yogurt, cottage cheese.
2. Know your protein target. Recommendations for people losing weight on these medications are higher than the standard minimum, and your target depends on your weight, age, and kidney health. That's exactly what a nutrition professional calculates for you [4].
3. Do strength work 2–3 times a week. Bands, weights, or your own bodyweight. Muscle that gets used is muscle the body keeps. Walking is great, but it doesn't replace strength.
4. Don't go whole days barely eating. A small appetite doesn't mean zero fuel. Small, protein-dense meals beat one large meal your stomach can't handle.
5. Watch your micronutrients. B12, iron, and vitamin D deficiencies are common when total intake drops. Labs every few months is a smart habit; review them with your physician or nutrition professional [4].

This article is educational and does not replace medical care. Never start, stop, or change a medication dose without your physician. TONE Health does not sell or promote medications; brand names belong to their owners and are mentioned for identification only.