TL;DR: Ozempic, Wegovy and Mounjaro can reduce fat and lean mass. Trial measurements of lean mass do not equal skeletal muscle alone. Protein, progressive resistance training and practical monitoring help protect strength and make weight loss easier to maintain.
A lower weight is not always the same as a better body.
When people use Ozempic, Wegovy or Mounjaro and the scale goes down, the useful question is simple: what was actually lost? Fat, muscle, or both?
This distinction matters because Élan is not trying to create lighter patients for a few months. We are trying to help people maintain the result with strength, health and a lower risk of regain.
The risk during fast weight loss
When calories are low and protein is not planned carefully, the body can lose muscle alongside fat.
We should be careful with exact percentages. Different studies measure body composition differently, and not every claim online is well supported. The practical message is still clear: without a specific plan, a meaningful part of weight loss can include lean tissue, not only fat.
Lean mass is not the same as skeletal muscle. DXA and similar trial measurements group muscle with water, glycogen, organs and other non-fat tissue. A fall in lean mass can still matter, but it should not be reported as if every kilogram were muscle.
For a patient, excessive muscle loss can mean feeling weaker, recovering less well and having less capacity for the physical activity that supports long-term weight maintenance. Risk deserves particular attention in older adults, people with low baseline strength and people whose food intake has fallen sharply.
Why muscle matters
Muscle is not only about appearance or physical performance.
It matters for daily function: getting up from a chair, managing stairs, carrying shopping, keeping up with children or grandchildren. People on Ozempic, Wegovy or Mounjaro are often already working on improving their health broadly. Maintaining physical capacity is part of that work.
Muscle also matters for metabolic health. It plays a role in glucose handling and energy use. Preserving it during weight loss is not a cosmetic goal. It is a health goal.
What a muscle-preserving plan includes
Protein. Adequate protein intake supports muscle protein synthesis during a caloric deficit. The exact target should be individual, especially in kidney disease or other medical conditions, but most people eating significantly less food than before will not automatically get enough protein without planning.
Resistance training. Walking is good for health, but it does not replace progressive strength work. Lifting, bodyweight work and resistance bands provide the stimulus the body needs to maintain muscle when in a deficit. The programme does not need to be extreme. It needs to be consistent.
Monitoring more than weight. Body composition matters more than weight alone. If someone is losing scale weight but losing muscle instead of fat, the number on the scale tells an incomplete story. Waist measurement, physical performance, and ideally body composition testing give a clearer picture.
Not under-eating as a badge of honour. Very low food intake may speed short-term weight loss, but it increases the risk of lean mass loss and makes sustainable activity harder. The goal is a deficit that the body can manage, not a deficit that exhausts it.
In a DXA substudy of SURMOUNT-1, Look M et al. (Diabetes, Obesity and Metabolism, 2025; n=160) found that about 75% of weight lost with tirzepatide was fat mass and about 25% was lean mass. This was a small substudy, and lean mass was not the same as skeletal muscle. It supports monitoring, not alarmist claims.
Preserve the result, not only the number.
At Élan Clinic, we treat body composition as a central part of weight management. A structured consultation can build a plan around protein, training and body composition monitoring so weight loss is easier to maintain and regain risk is lower.
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- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine. 2021;384:989-1002. Randomised trial, n=1,961.
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine. 2022;387(3):205-216. Randomised trial, n=2,539.
- Look M et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study. Diabetes, Obesity and Metabolism. 2025;27(5):2720-2729. DXA substudy, n=160. PMID: 39996356.
- Phillips SM, Van Loon LJC. Dietary protein for athletes: from requirements to optimum adaptation. Journal of Sports Sciences. 2011;29 Suppl 1:S29-S38. Expert review.