GLP-1 use among U.S. adults has nearly quadrupled since 2024, and more people than ever are watching a number on the scale go down week after week (Gallup, 2026). But weight lost isn't automatically fat lost. Some of that drop is muscle, and once it's gone, it's a lot harder to rebuild than it was to keep in the first place.
The short answer: You don't have to choose between losing weight and keeping your muscle. Eating enough protein, roughly 1.2 to 1.6 grams per kilogram of body weight a day, and doing resistance training two to three times a week protects lean mass while you lose fat, even on a GLP-1 medication.
Why losing weight can mean losing muscle
Any time you eat in a calorie deficit, your body pulls energy from wherever it can get it, and that includes muscle tissue, not just fat stores. Cut calories hard enough, or fast enough, and your body will happily break down muscle right alongside body fat to make up the difference.
That's not a sign you're doing something wrong. It's just how the body manages a fuel shortage, and it's exactly why "eat less, move more" on its own is an incomplete strategy. The fix isn't eating more calories overall. It's making sure the food and effort you do put in are specifically protecting muscle, not just moving a number on the scale.
This is why two people can lose the exact same 20 pounds and end up in very different places. One loses mostly fat and keeps their strength and shape. The other loses a meaningful chunk of muscle along with the fat, ends up softer and weaker at the same body weight, and often finds the weight comes back faster afterward, since muscle is one of the biggest drivers of daily calorie burn.
The real lever: protein, not just less food
Muscle is maintained through a constant cycle of breakdown and rebuilding called muscle protein synthesis. When you're eating less, that cycle tips toward breakdown unless you give your body enough raw material, specifically protein, to keep rebuilding what's being broken down.
A meta-analysis pooling 47 studies and more than 3,200 participants found that higher protein intake during weight loss consistently preserved lean mass and improved body composition compared to standard, lower-protein diets. The International Society of Sports Nutrition puts the effective range at 1.6 to 2.2 grams of protein per kilogram of body weight per day for anyone pairing a calorie deficit with resistance training, and research suggests intake below 1.0 gram per kilogram is linked to a higher risk of muscle loss.
What that looks like in practice
- A 70 kg (about 155 lb) person: roughly 112 to 154 grams of protein a day on the higher end
- Spread across 3 to 4 meals, that's about 30 to 40 grams per meal, not one giant dinner
- Simple examples: eggs and Greek yogurt at breakfast, a chicken or tofu bowl at lunch, a protein shake as an easy top-up between meals
Resistance training matters more than cardio right now
Cardio burns calories, but it doesn't send your body a strong signal to hold onto muscle. Resistance training does. Lifting weights, especially compound movements like squats, deadlifts, rows, and presses, tells your body that muscle is still being used and is worth keeping around.
A realistic starting point
1 Train 2 to 3 times a week
Full body each session.
2 Prioritize compound lifts
Choose compound movements over isolation exercises.
3 Add progressive overload
Add a little more weight or a rep or two every week or two.
4 Keep cardio as a bonus
Keep it if you enjoy it, but treat it as a bonus, not the main event.
If you're using a GLP-1, this matters even more
GLP-1 medications like semaglutide and tirzepatide work largely by reducing appetite, which is exactly what makes them effective for weight loss. It's also what makes muscle loss a bigger risk. When you're eating a lot less overall, it's easy to fall short on protein without noticing. Research presented at the Endocrine Society's 2026 annual meeting found that physical activity actually tends to decrease among adults losing weight on GLP-1 medications, not increase, which removes one of the body's strongest signals to hold onto muscle.
Eating less protein and moving less at the same time is the exact combination that puts muscle at risk. The fix is the same as above: prioritize protein at every meal, even when appetite is low, and keep some resistance training in the week, even if it's just two shorter sessions.
If you're on a GLP-1 medication, talk with your prescribing provider before making significant changes to your protein intake or exercise routine, especially if you have other health conditions.
How to tell if it's actually working
The scale can't tell fat loss from muscle loss, so it's worth tracking a couple of other signals alongside your weight.
- Strength trend: are your working weights holding steady or climbing, not sliding backward, over a few weeks?
- How clothes fit through the shoulders, arms, and legs, not just the waist
- Energy during workouts: dragging through every session is a sign you may need more food or protein, not less
Your first week
1 Day 1
Full-body resistance session (squats, rows, push-ups).
2 Day 2
Rest or light walk, protein at every meal.
3 Day 3
Full-body resistance session (deadlift or hip hinge, press, core).
4 Day 4
Rest or light cardio.
5 Day 5
Full-body resistance session.
6 Day 6 to 7
Active rest, keep protein consistent even on lower-activity days.
Wrap-Up
Weight loss and muscle loss aren't the same goal, even though they can look identical on a scale. Protein and resistance training are what separate the two, whether you're losing weight through food alone or alongside a GLP-1 medication. Protect the muscle, and the number on the scale ends up meaning a lot more.
Frequently Asked Questions
Will lifting weights slow down my weight loss?
No. Resistance training doesn't meaningfully change your calorie deficit, and preserving muscle actually helps keep your metabolism higher as you lose weight.
How much protein is too much?
For most healthy adults, up to about 2.2 grams per kilogram of body weight a day is considered safe by sports nutrition research. Going higher generally doesn't add extra benefit.
Can I prevent muscle loss with cardio alone?
Cardio alone usually isn't enough. Resistance training is the specific signal that tells your body to keep muscle, while cardio mostly just burns calories.
Do I need a protein supplement, or can I get enough from food?
Food first is ideal, but a shake is a convenient way to close the gap on busy days or when appetite is low, especially on a GLP-1 medication.
Does it matter when I eat my protein during the day?
Spreading it across 3 to 4 meals matters more than exact timing. Aim for at least 25 to 30 grams per meal instead of loading it all into dinner.