GLP-1 · Evidence-based

On a GLP-1? How to lose fat without losing your strength

By Edgar Calleros · TONE Health · July 2026 · 5 min read

The scale is finally moving. Your appetite is quiet for the first time in years. And then someone tells you: "careful, you're losing muscle too." Is that true? Should you worry?

Short answer: it's a real risk, and it's largely preventable. Here's what the research actually says, in plain language.

What the studies show

GLP-1 receptor agonist medications, such as semaglutide and tirzepatide, produce significant weight loss in clinical trials. But when researchers measured what kind of weight was lost, they found something important: in the STEP 1 trial of semaglutide, body-composition data showed that roughly 40% of the total weight lost was lean mass, not fat [1].

There's a second finding worth knowing. In the STEP 1 extension study, participants who stopped the medication regained about two-thirds of the weight they had lost within a year [2]. The people who did best were those who had built eating and activity habits during treatment, not instead of it.

Why it happens

These medications lower your appetite dramatically. That's how they work. But when you eat much less overall, you usually eat much less protein too, and protein is the raw material your muscles need. Add rapid weight loss and less physical activity, and your body starts using muscle for fuel.

Five things you can do this week

1. Make protein the first thing on your plate. When your appetite is small, eat the protein first. Eggs, fish, chicken, beans with cheese, Greek yogurt, cottage cheese.
2. Know your protein target. General recommendations for adults losing weight on these medications are higher than the standard minimum, and your personal target depends on your weight, age and kidney health. This is exactly what a nutrition professional calculates for you [3].
3. Do resistance work 2 to 3 times a week. Bands, weights or bodyweight. Muscle that gets used is muscle your body keeps. Walking is great, but it doesn't replace resistance training.
4. Don't skip entire days of eating. Tiny 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 food intake drops. Lab work every few months is a smart habit; review it with your doctor or nutrition professional [3].

The bigger picture

The medication opens a window: less hunger, less food noise, real momentum. Nutrition is what you build inside that window, and it's what remains if you and your doctor ever decide to stop. That's not a scare tactic; it's the most hopeful part. Habits are yours to keep.

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