Independent UK medicine guidance
Mounjaro muscle loss: protein and strength training
Weight lost while taking Mounjaro is not exclusively body fat. As with other forms of significant weight loss, some lean mass will usually be lost as well. This guide explains what the research actually found and how protein and resistance exercise may help.
What the research found
Why does preserving muscle matter?
- Strength and mobility
- Balance
- Physical independence
- Glucose management
- Recovery from illness
- Long-term metabolic health
Older adults, people losing weight rapidly and anyone starting with relatively low muscle mass may need particular support.
Eat for nutrition, not just a lower number
Mounjaro can make eating much easier to control, but extremely low intake is not the objective. Include a protein-containing food in your meals where possible. Options include:
- Fish, chicken or lean meat
- Eggs
- Milk, yoghurt and cheese
- Beans, lentils and chickpeas
- Tofu, tempeh and other soya foods
- Nuts and seeds
Use your muscles
Resistance exercise gives the body a reason to retain strength and muscle during weight loss. This could include weights, resistance bands, gym machines, bodyweight exercises or suitably adapted strength work.
Start at an appropriate level and build gradually. A physiotherapist or qualified exercise professional can help if you have joint pain, disability or a long period of inactivity.
When should you ask for help?
Speak to your healthcare team if you develop:
- Increasing weakness
- Difficulty getting out of a chair
- Frequent falls
- Very rapid or uncontrolled weight loss
- Persistent inability to eat adequate meals
- Repeated vomiting
- Signs of malnutrition
Common questions
Does Mounjaro cause muscle loss?
Weight lost while taking Mounjaro is not exclusively body fat. In a 160-person body-composition substudy of SURMOUNT-1, approximately 75% of the weight lost with tirzepatide was fat mass and 25% was lean mass. Lean mass includes water, organs and other non-fat tissue as well as skeletal muscle, so it does not mean a quarter of everyone’s weight loss is muscle.
How much protein should I eat on Mounjaro?
There is no single protein target suitable for everyone. Requirements differ with body size, age, activity, kidney health and other medical conditions. Include a protein-containing food in meals where possible, and ask a registered dietitian for personalised advice, particularly if you have kidney disease.
Does exercise help protect muscle during weight loss?
Resistance exercise gives the body a reason to retain strength and muscle during weight loss. That could include weights, resistance bands, gym machines, bodyweight exercises or suitably adapted strength work. Start at an appropriate level and build gradually.
Related guides
Sources: SURMOUNT-1 body-composition substudy • Guy’s and St Thomas’ dietary advice for weight-loss medicines
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Sources referenced on this page
Standing primary references for every Monj page:
- Mounjaro (tirzepatide) Summary of Product Characteristics and Patient Information Leaflet, electronic medicines compendium
- MHRA Drug Safety Update: GLP-1 receptor agonists
- NICE TA1026: tirzepatide for managing overweight and obesity
- General Pharmaceutical Council register of pharmacies
- MHRA Yellow Card scheme
