Yes, you can lose muscle on GLP-1 medication. Part of the weight that comes off is lean mass, not just fat. The best protection is a plan you build with your prescriber and a coach: enough protein spread across the day, strength training two to three times a week, small meals you can tolerate, and tracking your strength, not just the scale.
I'm a nutrition coach and IFBB Pro in Carlsbad. I don't judge weight-loss medication and I don't manage it. Dosing, side effects and whether to start or stop belong with your prescriber. My lane is making sure as much of the weight you lose as possible is fat.
This post is about protecting muscle while you're on medication. If you're planning for life after it, read How to Keep Weight Off After GLP-1 Medication.
How much muscle can you lose on a GLP-1?
It can be a meaningful share. In a body-composition substudy of the STEP 1 trial, about 62% of the weight participants lost was fat and 38% was lean mass. Lean mass includes water, organs and connective tissue, so it isn't all muscle. Still, it's enough that protecting muscle belongs in every plan.
Those numbers come from a 2025 joint advisory on nutrition for people on GLP-1 therapy, written by the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society (Mozaffarian et al., Obesity, 2025). The authors estimated that roughly a fifth of the total weight lost was muscle.
This matters more after 40, when muscle tends to decline unless you work to keep it. Muscle helps you manage blood sugar, keeps you strong and is a big part of what makes a body look firm instead of just smaller. More in Weight Loss After 40 for Women.
How much protein do I need on a GLP-1?
Usually more than you feel like eating. The joint advisory suggests many adults on GLP-1 therapy set an absolute target of about 80 to 120 grams of protein a day, and notes that higher targets of 1.2 to 1.6 g per kilogram of body weight have been proposed during active weight loss. Your prescriber should confirm your number.
If you have kidney disease or another condition, your target needs medical input. For healthy women, here's how I make the number work when you're full after six bites:
Protein first. The advisory suggests eating protein-rich foods first in a meal.
Go dense. Greek yogurt, cottage cheese, eggs, fish, chicken, tofu, lean beef and a quality protein shake give you the most protein per bite.
Spread it out. Three or four smaller protein-forward meals are easier on a quiet appetite than one big plate.
Sip between meals. Drink fluids between meals so water doesn't fill you up before the protein does.
Is protein enough to protect muscle?
No. Protein is the building material, but strength training is the signal that tells your body to keep muscle. The joint advisory states that higher protein alone is likely inadequate to preserve muscle mass and pairs it with structured resistance training. You need both, starting now, not after the weight is off.
In a New England Journal of Medicine trial, older adults with obesity followed a weight-loss program plus aerobic training, resistance training, or both. Lean mass dropped about 5% in the aerobic-only group, compared with about 2% with resistance training and 3% with combined training. The combined group also improved physical function the most (Villareal et al., NEJM, 2017). No medication was involved, but the principle carries over: when you eat less, lifting protects muscle.
What strength training plan works on a GLP-1?
Two to three full-body strength sessions a week, built on squats, hinges, pushes, pulls and carries, with weights heavy enough that the last few reps are challenging. Add daily walking. Start lighter if you're new or low on energy, and progress gradually. Get your doctor's okay first if you have a medical condition.
The U.S. Physical Activity Guidelines recommend muscle-strengthening activity for all major muscle groups at least two days a week (HHS, 2018). That's the floor. On medication, I treat it as non-negotiable.
A simple week for a client in Carlsbad or Encinitas looks like this:
Day 1: goblet squat, dumbbell row, incline push-up, hip thrust, farmer's carry.
Day 2: Romanian deadlift, lat pulldown, dumbbell press, split squat, plank.
Day 3 (optional): repeat Day 1 with slightly heavier weights.
Most days: a 20 to 30 minute walk.
If nausea or low energy hits on a training day, shorten the session instead of skipping it. My full beginner breakdown is in Strength Training After 40 for Women in North County San Diego.
What should I eat on days I'm not hungry?
Small, protein-led mini-meals every few hours, with fluids in between. The joint advisory recommends smaller, more frequent meals, adequate fluids, a gradual increase in fiber, and keeping alcohol to a minimum. Low appetite is not a reason to skip protein. It's the reason to plan it ahead of time.
My clients' "low appetite menu" usually includes:
A cup of cottage cheese or Greek yogurt with berries.
Two eggs and a slice of whole-grain toast.
A protein shake made with milk or a fortified soy drink.
A few ounces of salmon or chicken with soft-cooked vegetables.
The advisory also flags nutrients that can run low when you eat much less, including iron, calcium, magnesium, vitamin D and B12. Ask your prescriber whether you need labs or a supplement. Don't guess.
How do I know if I'm losing muscle or fat?
Watch your strength, not just the scale. If your lifts are holding steady or climbing while your weight drops, that's a good sign you're keeping muscle. If you're getting weaker, more tired and softer while the scale falls, it's time to review protein, training and recovery with your coach and your prescriber.
What I track with clients:
Strength numbers on a few key lifts, every week.
Waist measurement and how clothes fit.
Energy, sleep and recovery. Short sleep makes everything harder, including holding onto muscle.
Key takeaways
Part of the weight lost on a GLP-1 is lean mass. In one major substudy, it was about 38% of the total.
Many adults on GLP-1 therapy are advised to get roughly 80 to 120 g of protein a day. Confirm your number with your prescriber.
Protein alone isn't enough. Lift two to three times a week and walk daily.
On low-appetite days, use small, protein-first meals.
Track strength, not just weight. Medication decisions stay with your prescriber.
FAQ
Does everyone lose muscle on a GLP-1?
Most people lose some lean mass whenever they lose weight, with or without medication. How much varies from person to person. Eating enough protein and strength training regularly are the two levers with the best support for keeping more of it.
Can I build muscle while on a GLP-1?
Some women, especially those new to lifting, gain strength and even some muscle while losing fat. For most, the realistic goal is to hold onto muscle while fat comes off. Rising strength numbers are a great sign you're on track.
Is walking enough to protect muscle on a GLP-1?
Walking is great for heart health, blood sugar and mood, but it doesn't load your muscles enough to protect them. Pair daily walking with two to three strength sessions a week.
Do I need protein shakes on a GLP-1?
Not necessarily. Whole foods work if you can eat enough of them. Shakes are a practical backup on low-appetite days because they deliver a lot of protein in a small volume. Check with your prescriber if you have kidney disease.
Do you coach women on GLP-1 medication in Carlsbad?
Yes. I coach women 40+ across Carlsbad and North County San Diego on protein, strength training and habits, alongside their prescriber's care. I never advise on dosing or stopping medication. Apply for private coaching or call or text (760) 334-9500.
About the author
Juliana Garcia is a nutrition and strength coach based in Carlsbad, California, and the founder of Unleash Her Vitality (UHV Wellness). She holds degrees in Nutrition and Psychology, competes as an IFBB Pro, and has coached fitness and nutrition for more than 20 years. Juliana coaches women 40+ privately across North County San Diego. She is a coach, not a medical provider, and works alongside her clients' doctors. More about Juliana.
This article is for education only and isn't medical advice. Talk with your doctor before changing your medication, treatment or exercise routine.
Ready for a plan built around you?
Private coaching for women 40+ in Carlsbad and North County San Diego is by application, with limited client spots. Apply for private coaching, or call or text (760) 334-9500.