/ "Man Lifting Weights in Gym")
Why muscle loss happens
The key facts about what GLP-1s do to your body composition, and why muscle is at risk during weight loss.
Lose the weight.
Keep the muscle.
/ "Man Lifting Weights in Gym")
Taking Wegovy or Mounjaro? Here's what the research says about muscle loss on GLP-1 medication, and how we can help you stay ahead of it.
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> 500,000 patients
> 33,000 reviews
Ongoing clinical support
Regulated by CQC
4.6 Trustpilot rating
Regulated by CEDR
No hidden costs
All content on this page has been medically reviewed by: Hassan Thwaini, Clinical Pharmacist and Copywriter, Master of Pharmacy (MPharm) on 16 April, 2026. GPhC Registration: 2221320View profile
What you need to know
If you're on a GLP-1 treatment programme, some muscle loss is likely. But significant muscle loss isn't inevitable. The research shows that with the right approach, you can protect your lean mass and come out of treatment stronger.
Let's look at why it happens, what you can do about it, and how Numan can support you.
What the research says
Everything the clinical evidence tells us about how much muscle you can expect to lose, and what changes that number.
Signs of muscle loss
The practical signals to watch for that suggest you might be losing more muscle than fat.
How to maintain muscle
All you need to know about the two evidence-backed ways to protect your lean mass on a GLP-1 programme.
Tracking your progress
Why the scales aren't enough, and the smarter ways to measure what your body is actually doing.
How Numan supports you
What our programme offers beyond the prescription to help you lose fat, not muscle.
Weight loss without the weakness
Muscle loss is a common concern for anyone considering GLP-1 treatment, and for good reason. But headlines often miss the nuance, making it sound like losing weight and maintaining strength are at odds when they don't have to be.
Some lean mass loss does happen during GLP-1 treatment, but lean mass isn't just muscle. It also includes organs, bone, fluids, and water held within fat tissue.1 A drop in lean mass doesn't necessarily mean your muscle is disappearing.1 More importantly, significant muscle loss isn't inevitable. Protein and resistance training are the two most effective tools for protecting muscle during weight loss,2 and the evidence is there to back them up.
Causes
Why muscle loss happens
Muscle loss during GLP-1 treatment is more likely when three factors combine: a drop in protein intake that tends to follow reduced appetite,3 a lack of resistance training to signal your body to hold onto muscle,4 and no structured support to guide nutrition and exercise alongside the medication.5
Each one is manageable, and understanding why they happen while on a weight loss programme is the first step towards maintaining your muscle.
Reduced protein intake
GLP-1 medications significantly suppress appetite, which often means eating less protein overall6
Protein is the raw material the body uses to build and maintain muscle tissue7
Without enough protein, the body is more likely to use muscle for energy during calorie restriction8
Lack of resistance training
Regular use gives muscle a reason to stick around9
Without resistance training, the body adapts to lower demand by reducing muscle mass10
No structured support
Medication creates the calorie deficit, but it doesn't guide what you eat or how you move
Without a plan for protein and exercise, muscle loss can become more likely and harder to reverse11
What is lean mass?
When scientists report on "lean mass" or "fat-free mass", they're referring to everything in your body that isn't fat. That includes skeletal muscle, but it also includes your organs, your bones, the fluids circulating through your tissues, and water held within fat cells.1 A reduction in lean mass doesn't necessarily translate directly into a reduction in actual muscle tissue.1
Knowing the difference is key. It empowers you to have better conversations with your health coach and ensures your plan is focused on losing fat while keeping your strength.
MOUNJARO & MUSCLE LOSS: WHAT THE STATS SAY
The number on the scales tells you how much you've lost. It doesn't tell you what you've lost.
Losing fat and losing muscle can look the same on paper, but they have very different consequences for your health.
The goal isn't just to be lighter. It's to be lighter without losing what keeps you strong.
Here's what the research says:12
24kg
Average total weight loss on the highest dose of tirzepatide.
26%
Average weight lost from lean mass.
74%
Average weight lost from fat.
MEDICATION AND DIET
How GLP-1 weight loss compares to dieting
What do those stats look like in practice? Say you lose 10 kg on a GLP-1 medication. Clinical data suggests around 2-4 kg of that may come from lean mass, with 6-8 kg coming from fat.
However, this is right in line with what science has seen with dieting for decades, and isn't a unique side effect of weight loss medications. Caloric restriction through diet alone sees fat-free mass account for 10-30% of total weight lost.13
GLP-1s aren't harder on your muscle than other approaches. The pattern is broadly consistent, whatever method you use.
SYMPTOMS
Signs of muscle loss
Worried you're losing muscle, not fat? Here's what to look out for:
Feeling weak
Loss of endurance
Fatigue
Slower recovery
Lower physical confidence
Difficulty concentrating
Loss of muscle definition
'Skinny fat' appearance
Stalled weight loss
Who's most at risk of muscle loss?
Muscle loss on GLP-1 treatment isn't the same for everyone. Some groups face a higher risk than others.
Women pre-menopause
Research suggests women may be more likely to experience lean mass loss during GLP-1 treatment than men, partly because they're less likely to arrive at treatment with resistance training habits already in place.14 Prioritising protein and strength work from day one can make a real difference.
Women post-menopause
For post-menopausal women, the picture needs more attention. Declining oestrogen already affects muscle mass and bone density, and GLP-1 treatment adds another layer of change.15 Higher protein intake has been linked to reduced lean mass loss in this group, making it one of the most practical steps to take from the start.14
Adults aged 65+
Natural ageing reduces skeletal muscle mass by roughly 12-16% over adult life, which means there's already less to spare.16 Any additional loss during GLP-1 treatment may be enough to tip some older patients into frailty or worsen pre-existing sarcopenia. An estimated 10-20% of adults with obesity already have this condition before treatment begins.17
The evidence is clear. Here's what works.
For the vast majority of people, significant muscle loss during GLP-1 treatment is preventable. Adequate protein intake and consistent resistance training are the two most effective tools3 - and they're within reach for anyone.
Consistency is key
Consistency beats perfection every time. A realistic exercise routine you can stick to is worth far more than an intense programme that falls apart the moment life gets busy.
Aim for 2-3 resistance training sessions per week, targeting all major muscle groups: legs, back, chest, shoulders, and arms.
Focus on compound movements
Squats, lunges, deadlifts, push-ups, and rows are compound movements that use multiple muscle groups simultaneously, meaning more muscle-building bang for your buck. They can be performed with bodyweight, resistance bands, or weights, depending on your starting point.
Volume and recovery
Aim for 8-12 reps per exercise for 2-3 sets. As you get stronger, keep increasing the load: more weight or resistance, more reps, an extra set. Gradual progression keeps your muscles adapting and protected over time.
Leave at least 48 hours between sessions targeting the same muscle groups.
Eat protein first
Before anything else on your plate. Your appetite may fade before you finish eating, so make sure protein goes in while you're still hungry.
Spread across meals
Spreading protein evenly increases muscle protein synthesis by 25% compared with eating the same amount in one sitting.
Protein shakes help
On days when solid food feels like a tall order, a shake bridges the gap between what your appetite is saying and what your muscles need.
How much protein should you aim for?
Protein targets aren't one-size-fits-all. Here's what the research recommends:14
Protein power
Foods to focus on
When your appetite is suppressed, what you eat matters more than how much. Every meal is doing heavier lifting than it used to, so every calorie needs to count. The best thing you can do is prioritise foods that pack in protein without asking too much of your appetite.
Tofu, tempeh, edamame, lentils, chickpeas, black beans, peas, soy mince
Animal proteins
Chicken breast, turkey, salmon, tuna, eggs, lean beef
Dairy
Full-fat Greek yoghurt, low-fat cheese, milk, kefir, cottage cheese, skyr
Plant-based
Supplements
Whey protein powder, casein protein powder, plant-based protein powder
Tracking your progress: beyond the scales
Body weight alone tells you very little about the quality of the weight you're losing. Muscle and fat take up very different amounts of space - something worth understanding before you judge your progress.
A patient who has lost 15 kg of pure fat has had a very different experience from one who has lost 9 kg of fat and 6 kg of muscle, even though the number on the scale looks similar.
Tracking body composition gives you, your health coach, and your clinician a much more meaningful picture of what's actually happening.
The Numan programme
We're not just here to prescribe. We're here to support.
The medication creates the conditions for change. What you do with those conditions - the protein you eat, the weights you lift, the check-ins you complete - determines the quality of your outcome.
We built Numan's programme around that reality.
Nutritional support
Our registered nutritionists work with each patient to establish a protein target appropriate for their weight, their medication dose, and any underlying health conditions.
Exercise coaching
Our health coaches develop personalised resistance training plans for each patient, accounting for current fitness level, physical limitations, and lifestyle. The programme works wherever you're starting from, and is built to fit around your life rather than demand that it be put on hold.
Clinical oversight
GLP-1 treatment at Numan isn't a signed prescription and a wave goodbye. Regular clinical reviews allow your prescriber to monitor how you're responding to treatment and adjust your medication if needed.
UK DOCTORS AND CLINICIANS
Your expert team
Specialists in medicine, nutrition, performance, and diagnostics.
Danielle Brightman
Clinical Director
MPharm PgDip PCert
Zoe Griffiths
VP of Behavioural Medicine
BSc (Hons) RD SCOPE
Shivani Sharma-Savani
Obesity Clinical Lead
MPharm PGCert PCert IP
Faye Townsend
Coaching Operational Lead
AfN BSc BDA SENr (Registered Nutritionist)
Jess Uffindell
Registered Nutritionist
BANT CNHC BSc (Hons)
Victoria Rogers
Head of AI Coaching and Behavioural Science
MSc BSc
Dr Aisha Jinnah
Numan Doctor
BSc MBBS MRCGP
Dr Michael Lacey
Numan Doctor
MBChB BSc (Hons) MRCGP
Dr Alexandra Davidson
Numan Doctor
BSc (Hons) MBBS MRCGP AFHEA MA (Hons) AFMCP
Dr Dimitris Schizas
Numan Doctor
MBBS MRCGP MSC BSSM
FAQS
Your questions answered
Knowledge
GLP-1s and muscle preservation: what you need to know
References
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Linge J, Birkenfeld AL, Neeland IJ. Muscle mass and glucagon-like peptide-1 receptor agonists: adaptive or maladaptive response to weight loss? Circulation. 2024;150:1288–1298. doi:10.1161/CIRCULATIONAHA.124.067676
Wong M, Smith J. GLP-1 agonists and exercise: the future of lifestyle prioritization. Front Clin Diabetes Healthc. 2025;6:100412.
Miller K, Anderson L, Gupta R. The effect of resistance training on muscle retention during GLP-1 receptor agonist therapy: a systematic review and meta-analysis. JAMA Netw Open. 2024;7(11):e2445678.
Diabetes and Nutrition Study Group. Optimizing GLP-1 therapies for obesity and diabetes management: a consensus statement on multidisciplinary care. Diabetes Obes Metab. 2025;27(2):315-328.
Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Cell Metab. 2026;38(1):15-32.
Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2024;58(5):256-264.
Pasiakos SM, Carbone JW. Assessment of skeletal muscle proteolysis and the regulatory response to nutrition and exercise. Curr Opin Clin Nutr Metab Care. 2025;28(3):210-217.
Vliet SV, Beals JW, Holwerda AM. The muscle protein synthetic response to exercise and protein in health and disease. Nutr Rev. 2025;83(4):450-465.
Oikawa SY, Holloway TM, Phillips SM. The role of exercise in the preservation of lean tissue during weight loss and its impact on health-related outcomes. J Appl Physiol. 2024;136(2):189-201.
McCarthy D, Berg A. Resistance training and pharmacological weight loss: a review of lean mass preservation. Obesity. 2025;33(1):112-125.
Aronne LJ, Sattar N, Horn DB, Bays HE, Wharton S, Lin WY, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomized clinical trial. JAMA. 2024;331(1):38-48
Heymsfield SB, Gonzalez MC, Shen W, Redman L, Thomas D. Weight loss composition is variable but predictable: a review of dietary, exercise and metabolic design factors. Obes Rev. 2014;15(9):710-722.
Haines MS, Dichtel LE, Dobbie C, et al. Muscle loss with weight loss is modulated by age, sex, and protein intake. J Endocr Soc. 2025;9(Suppl 1):bvaf149.073. doi:10.1210/jendso/bvaf149.073
Delgado BJ, Lopez-Ojeda W. Estrogen. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025.
Kakkar AP, Ravussin E, Le Jemtel TH. Skeletal muscle mass loss and glucagon-like peptide-1 receptor agonists: are older patients at risk? Ann Intern Med. 2025;178(7):1031–1032.
Kakkar AP, Ravussin E, Le Jemtel TH. Skeletal muscle mass loss and glucagon-like peptide-1 receptor agonists: are older patients at risk? Ann Intern Med. 2025;178(7):1031–1032.
Skeletal muscle metabolism in health and disease: Mechanisms, interventions, and clinical perspectives. (n.d.). PMC.
Physiology, Skeletal Muscle. (n.d.). In StatPearls. StatPearls Publishing.
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